Re: [PATCH v13 6/9] gfxstream + rutabaga: add initial support for gfxstream

[Akihiko Odaki <akihiko.odaki@xxxxxxxxx>]

On 2023/08/29 9:36, Gurchetan Singh wrote:
> This adds initial support for gfxstream and cross-domain.  Both
> features rely on virtio-gpu blob resources and context types, which
> are also implemented in this patch.
>
> gfxstream has a long and illustrious history in Android graphics
> paravirtualization.  It has been powering graphics in the Android
> Studio Emulator for more than a decade, which is the main developer
> platform.
>
> Originally conceived by Jesse Hall, it was first known as "EmuGL" [a].
> The key design characteristic was a 1:1 threading model and
> auto-generation, which fit nicely with the OpenGLES spec.  It also
> allowed easy layering with ANGLE on the host, which provides the GLES
> implementations on Windows or MacOS enviroments.
>
> gfxstream has traditionally been maintained by a single engineer, and
> between 2015 to 2021, the goldfish throne passed to Frank Yang.
> Historians often remark this glorious reign ("pax gfxstreama" is the
> academic term) was comparable to that of Augustus and both Queen
> Elizabeths.  Just to name a few accomplishments in a resplendent
> panoply: higher versions of GLES, address space graphics, snapshot
> support and CTS compliant Vulkan [b].
>
> One major drawback was the use of out-of-tree goldfish drivers.
> Android engineers didn't know much about DRM/KMS and especially TTM so
> a simple guest to host pipe was conceived.
>
> Luckily, virtio-gpu 3D started to emerge in 2016 due to the work of
> the Mesa/virglrenderer communities.  In 2018, the initial virtio-gpu
> port of gfxstream was done by Cuttlefish enthusiast Alistair Delva.
> It was a symbol compatible replacement of virglrenderer [c] and named
> "AVDVirglrenderer".  This implementation forms the basis of the
> current gfxstream host implementation still in use today.
>
> cross-domain support follows a similar arc.  Originally conceived by
> Wayland aficionado David Reveman and crosvm enjoyer Zach Reizner in
> 2018, it initially relied on the downstream "virtio-wl" device.
>
> In 2020 and 2021, virtio-gpu was extended to include blob resources
> and multiple timelines by yours truly, features gfxstream/cross-domain
> both require to function correctly.
>
> Right now, we stand at the precipice of a truly fantastic possibility:
> the Android Emulator powered by upstream QEMU and upstream Linux
> kernel.  gfxstream will then be packaged properfully, and app
> developers can even fix gfxstream bugs on their own if they encounter
> them.
>
> It's been quite the ride, my friends.  Where will gfxstream head next,
> nobody really knows.  I wouldn't be surprised if it's around for
> another decade, maintained by a new generation of Android graphics
> enthusiasts.
>
> Technical details:
>    - Very simple initial display integration: just used Pixman
>    - Largely, 1:1 mapping of virtio-gpu hypercalls to rutabaga function
>      calls
>
> Next steps for Android VMs:
>    - The next step would be improving display integration and UI interfaces
>      with the goal of the QEMU upstream graphics being in an emulator
>      release [d].
>
> Next steps for Linux VMs for display virtualization:
>    - For widespread distribution, someone needs to package Sommelier or the
>      wayland-proxy-virtwl [e] ideally into Debian main. In addition, newer
>      versions of the Linux kernel come with DRM_VIRTIO_GPU_KMS option,
>      which allows disabling KMS hypercalls.  If anyone cares enough, it'll
>      probably be possible to build a custom VM variant that uses this display
>      virtualization strategy.
>
> [a] https://android-review.googlesource.com/c/platform/development/+/34470
> [b] 
> https://android-review.googlesource.com/q/topic:%22vulkan-hostconnection-start%22
> [c] 
> https://android-review.googlesource.com/c/device/generic/goldfish-opengl/+/761927
> [d] https://developer.android.com/studio/releases/emulator
> [e] https://github.com/talex5/wayland-proxy-virtwl
>
> Signed-off-by: Gurchetan Singh <gurchetansingh@xxxxxxxxxxxx>
> Tested-by: Alyssa Ross <hi@xxxxxxxxx>
> Tested-by: Emmanouil Pitsidianakis <manos.pitsidianakis@xxxxxxxxxx>
> Tested-by: Akihiko Odaki <akihiko.odaki@xxxxxxxxxx>
> Reviewed-by: Emmanouil Pitsidianakis <manos.pitsidianakis@xxxxxxxxxx>
> Reviewed-by: Antonio Caggiano <quic_acaggian@xxxxxxxxxxx>
> Reviewed-by: Akihiko Odaki <akihiko.odaki@xxxxxxxxxx>
> ---
>   hw/display/virtio-gpu-pci-rutabaga.c |   47 ++
>   hw/display/virtio-gpu-rutabaga.c     | 1119 ++++++++++++++++++++++++++
>   hw/display/virtio-vga-rutabaga.c     |   50 ++
>   3 files changed, 1216 insertions(+)
>   create mode 100644 hw/display/virtio-gpu-pci-rutabaga.c
>   create mode 100644 hw/display/virtio-gpu-rutabaga.c
>   create mode 100644 hw/display/virtio-vga-rutabaga.c
>
> diff --git a/hw/display/virtio-gpu-pci-rutabaga.c 
> b/hw/display/virtio-gpu-pci-rutabaga.c
> new file mode 100644
> index 0000000000..c96729e198
> --- /dev/null
> +++ b/hw/display/virtio-gpu-pci-rutabaga.c
> @@ -0,0 +1,47 @@
> +/* SPDX-License-Identifier: GPL-2.0-or-later */
> +
> +#include "qemu/osdep.h"
> +#include "qapi/error.h"
> +#include "qemu/module.h"
> +#include "hw/pci/pci.h"
> +#include "hw/qdev-properties.h"
> +#include "hw/virtio/virtio.h"
> +#include "hw/virtio/virtio-bus.h"
> +#include "hw/virtio/virtio-gpu-pci.h"
> +#include "qom/object.h"
> +
> +#define TYPE_VIRTIO_GPU_RUTABAGA_PCI "virtio-gpu-rutabaga-pci"
> +OBJECT_DECLARE_SIMPLE_TYPE(VirtIOGPURutabagaPCI, VIRTIO_GPU_RUTABAGA_PCI)
> +
> +struct VirtIOGPURutabagaPCI {
> +    VirtIOGPUPCIBase parent_obj;
> +
> +    VirtIOGPURutabaga vdev;
> +};
> +
> +static void virtio_gpu_rutabaga_initfn(Object *obj)
> +{
> +    VirtIOGPURutabagaPCI *dev = VIRTIO_GPU_RUTABAGA_PCI(obj);
> +
> +    virtio_instance_init_common(obj, &dev->vdev, sizeof(dev->vdev),
> +                                TYPE_VIRTIO_GPU_RUTABAGA);
> +    VIRTIO_GPU_PCI_BASE(obj)->vgpu = VIRTIO_GPU_BASE(&dev->vdev);
> +}
> +
> +static const TypeInfo virtio_gpu_rutabaga_pci_info[] = {
> +    {
> +        .name = TYPE_VIRTIO_GPU_RUTABAGA_PCI,
> +        .parent = TYPE_VIRTIO_GPU_PCI_BASE,
> +        .instance_size = sizeof(VirtIOGPURutabagaPCI),
> +        .instance_init = virtio_gpu_rutabaga_initfn,
> +        .interfaces = (InterfaceInfo[]) {
> +            { INTERFACE_CONVENTIONAL_PCI_DEVICE },
> +        }
> +    },
> +};
> +
> +DEFINE_TYPES(virtio_gpu_rutabaga_pci_info)
> +
> +module_obj(TYPE_VIRTIO_GPU_RUTABAGA_PCI);
> +module_kconfig(VIRTIO_PCI);
> +module_dep("hw-display-virtio-gpu-pci");
> diff --git a/hw/display/virtio-gpu-rutabaga.c b/hw/display/virtio-gpu-rutabaga.c
> new file mode 100644
> index 0000000000..a105e06214
> --- /dev/null
> +++ b/hw/display/virtio-gpu-rutabaga.c
> @@ -0,0 +1,1119 @@
> +/* SPDX-License-Identifier: GPL-2.0-or-later */
> +
> +#include "qemu/osdep.h"
> +#include "qapi/error.h"
> +#include "qemu/error-report.h"
> +#include "qemu/iov.h"
> +#include "trace.h"
> +#include "hw/virtio/virtio.h"
> +#include "hw/virtio/virtio-gpu.h"
> +#include "hw/virtio/virtio-gpu-pixman.h"
> +#include "hw/virtio/virtio-iommu.h"
> +
> +#include <glib/gmem.h>
> +#include <rutabaga_gfx/rutabaga_gfx_ffi.h>
> +
> +#define CHECK(condition, cmd)                                                 \
> +    do {                                                                      \
> +        if (!(condition)) {                                                   \
> +            error_report("CHECK failed in %s() %s:" "%d", __func__,           \
> +                         __FILE__, __LINE__);                                 \
> +            (cmd)->error = VIRTIO_GPU_RESP_ERR_UNSPEC;                        \
> +            return;                                                           \
> +       }                                                                      \
> +    } while (0)
> +
> +/*
> + * This is the size of the char array in struct sock_addr_un. No Wayland socket
> + * can be created with a path longer than this, including the null terminator.
> + */
> +#define UNIX_PATH_MAX sizeof((struct sockaddr_un) {} .sun_path)
> +
> +struct rutabaga_aio_data {
> +    struct VirtIOGPURutabaga *vr;
> +    struct rutabaga_fence fence;
> +};
> +
> +static void
> +virtio_gpu_rutabaga_update_cursor(VirtIOGPU *g, struct virtio_gpu_scanout *s,
> +                                  uint32_t resource_id)
> +{
> +    struct virtio_gpu_simple_resource *res;
> +    struct rutabaga_transfer transfer = { 0 };
> +    struct iovec transfer_iovec;
> +
> +    VirtIOGPURutabaga *vr = VIRTIO_GPU_RUTABAGA(g);
> +
> +    res = virtio_gpu_find_resource(g, resource_id);
> +    if (!res) {
> +        return;
> +    }
> +
> +    if (res->width != s->current_cursor->width ||
> +        res->height != s->current_cursor->height) {
> +        return;
> +    }
> +
> +    transfer.x = 0;
> +    transfer.y = 0;
> +    transfer.z = 0;
> +    transfer.w = res->width;
> +    transfer.h = res->height;
> +    transfer.d = 1;
> +
> +    transfer_iovec.iov_base = s->current_cursor->data;
> +    transfer_iovec.iov_len = res->width * res->height * 4;
> +
> +    rutabaga_resource_transfer_read(vr->rutabaga, 0,
> +                                    resource_id, &transfer,
> +                                    &transfer_iovec);
> +}
> +
> +static void
> +virtio_gpu_rutabaga_gl_flushed(VirtIOGPUBase *b)
> +{
> +    VirtIOGPU *g = VIRTIO_GPU(b);
> +    virtio_gpu_process_cmdq(g);
> +}
> +
> +static void
> +rutabaga_cmd_create_resource_2d(VirtIOGPU *g,
> +                                struct virtio_gpu_ctrl_command *cmd)
> +{
> +    int32_t result;
> +    struct rutabaga_create_3d rc_3d = { 0 };
> +    struct virtio_gpu_simple_resource *res;
> +    struct virtio_gpu_resource_create_2d c2d;
> +
> +    VirtIOGPURutabaga *vr = VIRTIO_GPU_RUTABAGA(g);
> +
> +    VIRTIO_GPU_FILL_CMD(c2d);
> +    trace_virtio_gpu_cmd_res_create_2d(c2d.resource_id, c2d.format,
> +                                       c2d.width, c2d.height);
> +
> +    rc_3d.target = 2;
> +    rc_3d.format = c2d.format;
> +    rc_3d.bind = (1 << 1);
> +    rc_3d.width = c2d.width;
> +    rc_3d.height = c2d.height;
> +    rc_3d.depth = 1;
> +    rc_3d.array_size = 1;
> +    rc_3d.last_level = 0;
> +    rc_3d.nr_samples = 0;
> +    rc_3d.flags = VIRTIO_GPU_RESOURCE_FLAG_Y_0_TOP;
> +
> +    result = rutabaga_resource_create_3d(vr->rutabaga, c2d.resource_id, 
> &rc_3d);
> +    CHECK(!result, cmd);
> +
> +    res = g_new0(struct virtio_gpu_simple_resource, 1);
> +    res->width = c2d.width;
> +    res->height = c2d.height;
> +    res->format = c2d.format;
> +    res->resource_id = c2d.resource_id;
> +
> +    QTAILQ_INSERT_HEAD(&g->reslist, res, next);
> +}
> +
> +static void
> +rutabaga_cmd_create_resource_3d(VirtIOGPU *g,
> +                                struct virtio_gpu_ctrl_command *cmd)
> +{
> +    int32_t result;
> +    struct rutabaga_create_3d rc_3d = { 0 };
> +    struct virtio_gpu_simple_resource *res;
> +    struct virtio_gpu_resource_create_3d c3d;
> +
> +    VirtIOGPURutabaga *vr = VIRTIO_GPU_RUTABAGA(g);
> +
> +    VIRTIO_GPU_FILL_CMD(c3d);
> +
> +    trace_virtio_gpu_cmd_res_create_3d(c3d.resource_id, c3d.format,
> +                                       c3d.width, c3d.height, c3d.depth);
> +
> +    rc_3d.target = c3d.target;
> +    rc_3d.format = c3d.format;
> +    rc_3d.bind = c3d.bind;
> +    rc_3d.width = c3d.width;
> +    rc_3d.height = c3d.height;
> +    rc_3d.depth = c3d.depth;
> +    rc_3d.array_size = c3d.array_size;
> +    rc_3d.last_level = c3d.last_level;
> +    rc_3d.nr_samples = c3d.nr_samples;
> +    rc_3d.flags = c3d.flags;
> +
> +    result = rutabaga_resource_create_3d(vr->rutabaga, c3d.resource_id, 
> &rc_3d);
> +    CHECK(!result, cmd);
> +
> +    res = g_new0(struct virtio_gpu_simple_resource, 1);
> +    res->width = c3d.width;
> +    res->height = c3d.height;
> +    res->format = c3d.format;
> +    res->resource_id = c3d.resource_id;
> +
> +    QTAILQ_INSERT_HEAD(&g->reslist, res, next);
> +}
> +
> +static void
> +rutabaga_cmd_resource_unref(VirtIOGPU *g,
> +                            struct virtio_gpu_ctrl_command *cmd)
> +{
> +    int32_t result;
> +    struct virtio_gpu_simple_resource *res;
> +    struct virtio_gpu_resource_unref unref;
> +
> +    VirtIOGPURutabaga *vr = VIRTIO_GPU_RUTABAGA(g);
> +
> +    VIRTIO_GPU_FILL_CMD(unref);
> +
> +    trace_virtio_gpu_cmd_res_unref(unref.resource_id);
> +
> +    res = virtio_gpu_find_resource(g, unref.resource_id);
> +    CHECK(res, cmd);
> +
> +    result = rutabaga_resource_unref(vr->rutabaga, unref.resource_id);
> +    CHECK(!result, cmd);
> +
> +    if (res->image) {
> +        pixman_image_unref(res->image);
> +    }
> +
> +    QTAILQ_REMOVE(&g->reslist, res, next);
> +    g_free(res);
> +}
> +
> +static void
> +rutabaga_cmd_context_create(VirtIOGPU *g,
> +                            struct virtio_gpu_ctrl_command *cmd)
> +{
> +    int32_t result;
> +    struct virtio_gpu_ctx_create cc;
> +
> +    VirtIOGPURutabaga *vr = VIRTIO_GPU_RUTABAGA(g);
> +
> +    VIRTIO_GPU_FILL_CMD(cc);
> +    trace_virtio_gpu_cmd_ctx_create(cc.hdr.ctx_id,
> +                                    cc.debug_name);
> +
> +    result = rutabaga_context_create(vr->rutabaga, cc.hdr.ctx_id,
> +                                     cc.context_init, cc.debug_name, cc.nlen);
> +    CHECK(!result, cmd);
> +}
> +
> +static void
> +rutabaga_cmd_context_destroy(VirtIOGPU *g,
> +                             struct virtio_gpu_ctrl_command *cmd)
> +{
> +    int32_t result;
> +    struct virtio_gpu_ctx_destroy cd;
> +
> +    VirtIOGPURutabaga *vr = VIRTIO_GPU_RUTABAGA(g);
> +
> +    VIRTIO_GPU_FILL_CMD(cd);
> +    trace_virtio_gpu_cmd_ctx_destroy(cd.hdr.ctx_id);
> +
> +    result = rutabaga_context_destroy(vr->rutabaga, cd.hdr.ctx_id);
> +    CHECK(!result, cmd);
> +}
> +
> +static void
> +rutabaga_cmd_resource_flush(VirtIOGPU *g, struct virtio_gpu_ctrl_command *cmd)
> +{
> +    int32_t result, i;
> +    struct virtio_gpu_scanout *scanout = NULL;
> +    struct virtio_gpu_simple_resource *res;
> +    struct rutabaga_transfer transfer = { 0 };
> +    struct iovec transfer_iovec;
> +    struct virtio_gpu_resource_flush rf;
> +    bool found = false;
> +
> +    VirtIOGPUBase *vb = VIRTIO_GPU_BASE(g);
> +    VirtIOGPURutabaga *vr = VIRTIO_GPU_RUTABAGA(g);
> +    if (vr->headless) {
> +        return;
> +    }
> +
> +    VIRTIO_GPU_FILL_CMD(rf);
> +    trace_virtio_gpu_cmd_res_flush(rf.resource_id,
> +                                   rf.r.width, rf.r.height, rf.r.x, rf.r.y);
> +
> +    res = virtio_gpu_find_resource(g, rf.resource_id);
> +    CHECK(res, cmd);
> +
> +    for (i = 0; i < vb->conf.max_outputs; i++) {
> +        scanout = &vb->scanout[i];
> +        if (i == res->scanout_bitmask) {
> +            found = true;
> +            break;
> +        }
> +    }
> +
> +    if (!found) {
> +        return;
> +    }
> +
> +    transfer.x = 0;
> +    transfer.y = 0;
> +    transfer.z = 0;
> +    transfer.w = res->width;
> +    transfer.h = res->height;
> +    transfer.d = 1;
> +
> +    transfer_iovec.iov_base = pixman_image_get_data(res->image);
> +    transfer_iovec.iov_len = res->width * res->height * 4;
> +
> +    result = rutabaga_resource_transfer_read(vr->rutabaga, 0,
> +                                             rf.resource_id, &transfer,
> +                                             &transfer_iovec);
> +    CHECK(!result, cmd);
> +    dpy_gfx_update_full(scanout->con);
> +}
> +
> +static void
> +rutabaga_cmd_set_scanout(VirtIOGPU *g, struct virtio_gpu_ctrl_command *cmd)
> +{
> +    struct virtio_gpu_simple_resource *res;
> +    struct virtio_gpu_scanout *scanout = NULL;
> +    struct virtio_gpu_set_scanout ss;
> +
> +    VirtIOGPUBase *vb = VIRTIO_GPU_BASE(g);
> +    VirtIOGPURutabaga *vr = VIRTIO_GPU_RUTABAGA(g);
> +    if (vr->headless) {
> +        return;
> +    }
> +
> +    VIRTIO_GPU_FILL_CMD(ss);
> +    trace_virtio_gpu_cmd_set_scanout(ss.scanout_id, ss.resource_id,
> +                                     ss.r.width, ss.r.height, ss.r.x, ss.r.y);
> +
> +    CHECK(ss.scanout_id < VIRTIO_GPU_MAX_SCANOUTS, cmd);
> +    scanout = &vb->scanout[ss.scanout_id];
> +
> +    if (ss.resource_id == 0) {
> +        dpy_gfx_replace_surface(scanout->con, NULL);
> +        dpy_gl_scanout_disable(scanout->con);
> +        return;
> +    }
> +
> +    res = virtio_gpu_find_resource(g, ss.resource_id);
> +    CHECK(res, cmd);
> +
> +    if (!res->image) {
> +        pixman_format_code_t pformat;
> +        pformat = virtio_gpu_get_pixman_format(res->format);
> +        CHECK(pformat, cmd);
> +
> +        res->image = pixman_image_create_bits(pformat,
> +                                              res->width,
> +                                              res->height,
> +                                              NULL, 0);
> +        CHECK(res->image, cmd);
> +        pixman_image_ref(res->image);
> +    }
> +
> +    vb->enable = 1;
> +
> +    /* realloc the surface ptr */
> +    scanout->ds = qemu_create_displaysurface_pixman(res->image);
> +    dpy_gfx_replace_surface(scanout->con, NULL);
> +    dpy_gfx_replace_surface(scanout->con, scanout->ds);
> +    res->scanout_bitmask = ss.scanout_id;
> +}
> +
> +static void
> +rutabaga_cmd_submit_3d(VirtIOGPU *g,
> +                       struct virtio_gpu_ctrl_command *cmd)
> +{
> +    int32_t result;
> +    struct virtio_gpu_cmd_submit cs;
> +    struct rutabaga_command rutabaga_cmd = { 0 };
> +    g_autofree uint8_t *buf = NULL;
> +    size_t s;
> +
> +    VirtIOGPURutabaga *vr = VIRTIO_GPU_RUTABAGA(g);
> +
> +    VIRTIO_GPU_FILL_CMD(cs);
> +    trace_virtio_gpu_cmd_ctx_submit(cs.hdr.ctx_id, cs.size);
> +
> +    buf = g_new0(uint8_t, cs.size);
> +    s = iov_to_buf(cmd->elem.out_sg, cmd->elem.out_num,
> +                   sizeof(cs), buf, cs.size);
> +    CHECK(s == cs.size, cmd);
> +
> +    rutabaga_cmd.ctx_id = cs.hdr.ctx_id;
> +    rutabaga_cmd.cmd = buf;
> +    rutabaga_cmd.cmd_size = cs.size;
> +
> +    result = rutabaga_submit_command(vr->rutabaga, &rutabaga_cmd);
> +    CHECK(!result, cmd);
> +}
> +
> +static void
> +rutabaga_cmd_transfer_to_host_2d(VirtIOGPU *g,
> +                                 struct virtio_gpu_ctrl_command *cmd)
> +{
> +    int32_t result;
> +    struct rutabaga_transfer transfer = { 0 };
> +    struct virtio_gpu_transfer_to_host_2d t2d;
> +
> +    VirtIOGPURutabaga *vr = VIRTIO_GPU_RUTABAGA(g);
> +
> +    VIRTIO_GPU_FILL_CMD(t2d);
> +    trace_virtio_gpu_cmd_res_xfer_toh_2d(t2d.resource_id);
> +
> +    transfer.x = t2d.r.x;
> +    transfer.y = t2d.r.y;
> +    transfer.z = 0;
> +    transfer.w = t2d.r.width;
> +    transfer.h = t2d.r.height;
> +    transfer.d = 1;
> +
> +    result = rutabaga_resource_transfer_write(vr->rutabaga, 0, t2d.resource_id,
> +                                              &transfer);
> +    CHECK(!result, cmd);
> +}
> +
> +static void
> +rutabaga_cmd_transfer_to_host_3d(VirtIOGPU *g,
> +                                 struct virtio_gpu_ctrl_command *cmd)
> +{
> +    int32_t result;
> +    struct rutabaga_transfer transfer = { 0 };
> +    struct virtio_gpu_transfer_host_3d t3d;
> +
> +    VirtIOGPURutabaga *vr = VIRTIO_GPU_RUTABAGA(g);
> +
> +    VIRTIO_GPU_FILL_CMD(t3d);
> +    trace_virtio_gpu_cmd_res_xfer_toh_3d(t3d.resource_id);
> +
> +    transfer.x = t3d.box.x;
> +    transfer.y = t3d.box.y;
> +    transfer.z = t3d.box.z;
> +    transfer.w = t3d.box.w;
> +    transfer.h = t3d.box.h;
> +    transfer.d = t3d.box.d;
> +    transfer.level = t3d.level;
> +    transfer.stride = t3d.stride;
> +    transfer.layer_stride = t3d.layer_stride;
> +    transfer.offset = t3d.offset;
> +
> +    result = rutabaga_resource_transfer_write(vr->rutabaga, t3d.hdr.ctx_id,
> +                                              t3d.resource_id, &transfer);
> +    CHECK(!result, cmd);
> +}
> +
> +static void
> +rutabaga_cmd_transfer_from_host_3d(VirtIOGPU *g,
> +                                   struct virtio_gpu_ctrl_command *cmd)
> +{
> +    int32_t result;
> +    struct rutabaga_transfer transfer = { 0 };
> +    struct virtio_gpu_transfer_host_3d t3d;
> +
> +    VirtIOGPURutabaga *vr = VIRTIO_GPU_RUTABAGA(g);
> +
> +    VIRTIO_GPU_FILL_CMD(t3d);
> +    trace_virtio_gpu_cmd_res_xfer_fromh_3d(t3d.resource_id);
> +
> +    transfer.x = t3d.box.x;
> +    transfer.y = t3d.box.y;
> +    transfer.z = t3d.box.z;
> +    transfer.w = t3d.box.w;
> +    transfer.h = t3d.box.h;
> +    transfer.d = t3d.box.d;
> +    transfer.level = t3d.level;
> +    transfer.stride = t3d.stride;
> +    transfer.layer_stride = t3d.layer_stride;
> +    transfer.offset = t3d.offset;
> +
> +    result = rutabaga_resource_transfer_read(vr->rutabaga, t3d.hdr.ctx_id,
> +                                             t3d.resource_id, &transfer, NULL);
> +    CHECK(!result, cmd);
> +}
> +
> +static void
> +rutabaga_cmd_attach_backing(VirtIOGPU *g, struct virtio_gpu_ctrl_command *cmd)
> +{
> +    struct rutabaga_iovecs vecs = { 0 };
> +    struct virtio_gpu_simple_resource *res;
> +    struct virtio_gpu_resource_attach_backing att_rb;
> +    int ret;
> +
> +    VirtIOGPURutabaga *vr = VIRTIO_GPU_RUTABAGA(g);
> +
> +    VIRTIO_GPU_FILL_CMD(att_rb);
> +    trace_virtio_gpu_cmd_res_back_attach(att_rb.resource_id);
> +
> +    res = virtio_gpu_find_resource(g, att_rb.resource_id);
> +    CHECK(res, cmd);
> +    CHECK(!res->iov, cmd);
> +
> +    ret = virtio_gpu_create_mapping_iov(g, att_rb.nr_entries, sizeof(att_rb),
> +                                        cmd, NULL, &res->iov, &res->iov_cnt);
> +    CHECK(!ret, cmd);
> +
> +    vecs.iovecs = res->iov;
> +    vecs.num_iovecs = res->iov_cnt;
> +
> +    ret = rutabaga_resource_attach_backing(vr->rutabaga, att_rb.resource_id,
> +                                           &vecs);
> +    if (ret != 0) {
> +        virtio_gpu_cleanup_mapping(g, res);
> +    }
> +
> +    CHECK(!ret, cmd);
> +}
> +
> +static void
> +rutabaga_cmd_detach_backing(VirtIOGPU *g, struct virtio_gpu_ctrl_command *cmd)
> +{
> +    struct virtio_gpu_simple_resource *res;
> +    struct virtio_gpu_resource_detach_backing detach_rb;
> +
> +    VirtIOGPURutabaga *vr = VIRTIO_GPU_RUTABAGA(g);
> +
> +    VIRTIO_GPU_FILL_CMD(detach_rb);
> +    trace_virtio_gpu_cmd_res_back_detach(detach_rb.resource_id);
> +
> +    res = virtio_gpu_find_resource(g, detach_rb.resource_id);
> +    CHECK(res, cmd);
> +
> +    rutabaga_resource_detach_backing(vr->rutabaga,
> +                                     detach_rb.resource_id);
> +
> +    virtio_gpu_cleanup_mapping(g, res);
> +}
> +
> +static void
> +rutabaga_cmd_ctx_attach_resource(VirtIOGPU *g,
> +                                 struct virtio_gpu_ctrl_command *cmd)
> +{
> +    int32_t result;
> +    struct virtio_gpu_ctx_resource att_res;
> +
> +    VirtIOGPURutabaga *vr = VIRTIO_GPU_RUTABAGA(g);
> +
> +    VIRTIO_GPU_FILL_CMD(att_res);
> +    trace_virtio_gpu_cmd_ctx_res_attach(att_res.hdr.ctx_id,
> +                                        att_res.resource_id);
> +
> +    result = rutabaga_context_attach_resource(vr->rutabaga, att_res.hdr.ctx_id,
> +                                              att_res.resource_id);
> +    CHECK(!result, cmd);
> +}
> +
> +static void
> +rutabaga_cmd_ctx_detach_resource(VirtIOGPU *g,
> +                                 struct virtio_gpu_ctrl_command *cmd)
> +{
> +    int32_t result;
> +    struct virtio_gpu_ctx_resource det_res;
> +
> +    VirtIOGPURutabaga *vr = VIRTIO_GPU_RUTABAGA(g);
> +
> +    VIRTIO_GPU_FILL_CMD(det_res);
> +    trace_virtio_gpu_cmd_ctx_res_detach(det_res.hdr.ctx_id,
> +                                        det_res.resource_id);
> +
> +    result = rutabaga_context_detach_resource(vr->rutabaga, det_res.hdr.ctx_id,
> +                                              det_res.resource_id);
> +    CHECK(!result, cmd);
> +}
> +
> +static void
> +rutabaga_cmd_get_capset_info(VirtIOGPU *g, struct virtio_gpu_ctrl_command *cmd)
> +{
> +    int32_t result;
> +    struct virtio_gpu_get_capset_info info;
> +    struct virtio_gpu_resp_capset_info resp;
> +
> +    VirtIOGPURutabaga *vr = VIRTIO_GPU_RUTABAGA(g);
> +
> +    VIRTIO_GPU_FILL_CMD(info);
> +
> +    result = rutabaga_get_capset_info(vr->rutabaga, info.capset_index,
> +                                      &resp.capset_id, 
> &resp.capset_max_version,
> +                                      &resp.capset_max_size);
> +    CHECK(!result, cmd);
> +
> +    resp.hdr.type = VIRTIO_GPU_RESP_OK_CAPSET_INFO;
> +    virtio_gpu_ctrl_response(g, cmd, &resp.hdr, sizeof(resp));
> +}
> +
> +static void
> +rutabaga_cmd_get_capset(VirtIOGPU *g, struct virtio_gpu_ctrl_command *cmd)
> +{
> +    int32_t result;
> +    struct virtio_gpu_get_capset gc;
> +    struct virtio_gpu_resp_capset *resp;
> +    uint32_t capset_size, capset_version;
> +    uint32_t current_id, i;
> +
> +    VirtIOGPURutabaga *vr = VIRTIO_GPU_RUTABAGA(g);
> +
> +    VIRTIO_GPU_FILL_CMD(gc);
> +    for (i = 0; i < vr->num_capsets; i++) {
> +        result = rutabaga_get_capset_info(vr->rutabaga, i,
> +                                          &current_id, &capset_version,
> +                                          &capset_size);
> +        CHECK(!result, cmd);
> +
> +        if (current_id == gc.capset_id) {
> +            break;
> +        }
> +    }
> +
> +    CHECK(i < vr->num_capsets, cmd);
> +
> +    resp = g_malloc0(sizeof(*resp) + capset_size);
> +    resp->hdr.type = VIRTIO_GPU_RESP_OK_CAPSET;
> +    rutabaga_get_capset(vr->rutabaga, gc.capset_id, gc.capset_version,
> +                        resp->capset_data, capset_size);
> +
> +    virtio_gpu_ctrl_response(g, cmd, &resp->hdr, sizeof(*resp) + capset_size);
> +    g_free(resp);
> +}
> +
> +static void
> +rutabaga_cmd_resource_create_blob(VirtIOGPU *g,
> +                                  struct virtio_gpu_ctrl_command *cmd)
> +{
> +    int result;
> +    struct rutabaga_iovecs vecs = { 0 };
> +    g_autofree struct virtio_gpu_simple_resource *res = NULL;
> +    struct virtio_gpu_resource_create_blob cblob;
> +    struct rutabaga_create_blob rc_blob = { 0 };
> +
> +    VirtIOGPURutabaga *vr = VIRTIO_GPU_RUTABAGA(g);
> +
> +    VIRTIO_GPU_FILL_CMD(cblob);
> +    trace_virtio_gpu_cmd_res_create_blob(cblob.resource_id, cblob.size);
> +
> +    CHECK(cblob.resource_id != 0, cmd);
> +
> +    res = g_new0(struct virtio_gpu_simple_resource, 1);
> +
> +    res->resource_id = cblob.resource_id;
> +    res->blob_size = cblob.size;
> +
> +    if (cblob.blob_mem != VIRTIO_GPU_BLOB_MEM_HOST3D) {
> +        result = virtio_gpu_create_mapping_iov(g, cblob.nr_entries,
> +                                               sizeof(cblob), cmd, &res->addrs,
> +                                               &res->iov, &res->iov_cnt);
> +        CHECK(!result, cmd);
> +    }
> +
> +    rc_blob.blob_id = cblob.blob_id;
> +    rc_blob.blob_mem = cblob.blob_mem;
> +    rc_blob.blob_flags = cblob.blob_flags;
> +    rc_blob.size = cblob.size;
> +
> +    vecs.iovecs = res->iov;
> +    vecs.num_iovecs = res->iov_cnt;
> +
> +    result = rutabaga_resource_create_blob(vr->rutabaga, cblob.hdr.ctx_id,
> +                                           cblob.resource_id, &rc_blob, &vecs,
> +                                           NULL);
> +
> +    if (result && cblob.blob_mem != VIRTIO_GPU_BLOB_MEM_HOST3D) {
> +        virtio_gpu_cleanup_mapping(g, res);
> +    }
> +
> +    CHECK(!result, cmd);
> +
> +    QTAILQ_INSERT_HEAD(&g->reslist, res, next);
> +    res = NULL;
> +}
> +
> +static void
> +rutabaga_cmd_resource_map_blob(VirtIOGPU *g,
> +                               struct virtio_gpu_ctrl_command *cmd)
> +{
> +    int32_t result;
> +    uint32_t map_info = 0;
> +    uint32_t slot = 0;
> +    struct virtio_gpu_simple_resource *res;
> +    struct rutabaga_mapping mapping = { 0 };
> +    struct virtio_gpu_resource_map_blob mblob;
> +    struct virtio_gpu_resp_map_info resp = { 0 };
> +
> +    VirtIOGPUBase *vb = VIRTIO_GPU_BASE(g);
> +    VirtIOGPURutabaga *vr = VIRTIO_GPU_RUTABAGA(g);
> +
> +    VIRTIO_GPU_FILL_CMD(mblob);
> +
> +    CHECK(mblob.resource_id != 0, cmd);
> +
> +    res = virtio_gpu_find_resource(g, mblob.resource_id);
> +    CHECK(res, cmd);
> +
> +    result = rutabaga_resource_map_info(vr->rutabaga, mblob.resource_id,
> +                                        &map_info);
> +    CHECK(!result, cmd);
> +
> +    /*
> +     * RUTABAGA_MAP_ACCESS_* flags are not part of the virtio-gpu spec, but do
> +     * exist to potentially allow the hypervisor to restrict write access to
> +     * memory. QEMU does not need to use this functionality at the moment.
> +     */
> +    resp.map_info = map_info & RUTABAGA_MAP_CACHE_MASK;
> +
> +    result = rutabaga_resource_map(vr->rutabaga, mblob.resource_id, &mapping);
> +    CHECK(!result, cmd);
> +
> +    for (slot = 0; slot < MAX_SLOTS; slot++) {
> +        if (vr->memory_regions[slot].used) {
> +            continue;
> +        }
> +
> +        MemoryRegion *mr = &(vr->memory_regions[slot].mr);
> +        memory_region_init_ram_ptr(mr, OBJECT(vr), "blob", mapping.size,
> +                                   mapping.ptr);
> +        memory_region_add_subregion(&vb->hostmem, mblob.offset, mr);
> +        vr->memory_regions[slot].resource_id = mblob.resource_id;
> +        vr->memory_regions[slot].used = 1;
> +        break;
> +    }
> +
> +    if (slot >= MAX_SLOTS) {
> +        result = rutabaga_resource_unmap(vr->rutabaga, mblob.resource_id);
> +        CHECK(!result, cmd);
> +    }
> +
> +    CHECK(slot < MAX_SLOTS, cmd);
> +
> +    resp.hdr.type = VIRTIO_GPU_RESP_OK_MAP_INFO;
> +    virtio_gpu_ctrl_response(g, cmd, &resp.hdr, sizeof(resp));
> +}
> +
> +static void
> +rutabaga_cmd_resource_unmap_blob(VirtIOGPU *g,
> +                                 struct virtio_gpu_ctrl_command *cmd)
> +{
> +    int32_t result;
> +    uint32_t slot = 0;
> +    struct virtio_gpu_simple_resource *res;
> +    struct virtio_gpu_resource_unmap_blob ublob;
> +
> +    VirtIOGPUBase *vb = VIRTIO_GPU_BASE(g);
> +    VirtIOGPURutabaga *vr = VIRTIO_GPU_RUTABAGA(g);
> +
> +    VIRTIO_GPU_FILL_CMD(ublob);
> +
> +    CHECK(ublob.resource_id != 0, cmd);
> +
> +    res = virtio_gpu_find_resource(g, ublob.resource_id);
> +    CHECK(res, cmd);
> +
> +    for (slot = 0; slot < MAX_SLOTS; slot++) {
> +        if (vr->memory_regions[slot].resource_id != ublob.resource_id) {
> +            continue;
> +        }
> +
> +        MemoryRegion *mr = &(vr->memory_regions[slot].mr);
> +        memory_region_del_subregion(&vb->hostmem, mr);
> +
> +        vr->memory_regions[slot].resource_id = 0;
> +        vr->memory_regions[slot].used = 0;
> +        break;
> +    }
> +
> +    CHECK(slot < MAX_SLOTS, cmd);
> +    result = rutabaga_resource_unmap(vr->rutabaga, res->resource_id);
Hi,

After the discussion with Xenia Ragiadakou regarding their patch for 
Venus, I found a bug present in the Venus implementation also affects 
Rutabaga.
The problem is that the memory region may not immediately go away with 
memory_region_del_subregion(), but it may be kept a bit after that. The 
memory region has a pointer to the mapped memory so the unmapping call 
that immediately follows will make it dangling.
Xenia raised a question whether the dangling pointer can be actually 
dereferenced and result in use-after-free, but the answer is 
unfortunately yes. For example, consider the following call chain:
kvm_cpu_exec -> address_space_rw -> address_space_write -> 
flatview_write -> flatview_write_continue
address_space_write() holds a RCU read lock so that the flatview it 
refers to will not go away during the operation even if it becomes 
obsolete and will be used for writes. It is possible that the obsolete 
flatview contains the memory region for the memory that is concurrently 
unmapped by virtio-gpu-rutabaga/virgl.  Note that the function can be 
called without holding BQL, and KVM actually does so.
Another case is address_space_map(). It acquires the reference to the 
memory with memory_region_ref() and expects it will be available until 
memory_region_unref() gets called with address_space_unmap().
In conclusion, both of Rutabaga and Virgl need to ensure to wait until 
all refrences to memory region will be gone before unmapping the 
underlying memory. The patch "[QEMU PATCH v5 07/13] softmmu/memory: 
enable automatic deallocation of memory regions" in the venus patch 
series is useful to know when that happens.
Regards,
Akihiko Odaki