[XEN][RFC PATCH v4 12/16] xen/arm: Implement device tree node removal functionalities

[Vikram Garhwal <vikram.garhwal@xxxxxxx>]

Introduce sysctl XEN_SYSCTL_dt_overlay to remove device-tree nodes added using
device tree overlay.

xl dt_overlay remove file.dtbo:
    Removes all the nodes in a given dtbo.
    First, removes IRQ permissions and MMIO accesses. Next, it finds the nodes
    in dt_host and delete the device node entries from dt_host.

    The nodes get removed only if it is not used by any of dom0 or domio.

Also, added overlay_track struct to keep the track of added node through device
tree overlay. overlay_track has dt_host_new which is unflattened form of updated
fdt and name of overlay nodes. When a node is removed, we also free the memory
used by overlay_track for the particular overlay node.

Nested overlay removal is supported in sequential manner only i.e. if
overlay_child nests under overlay_parent, it is assumed that user first removes
overlay_child and then removes overlay_parent.

Signed-off-by: Vikram Garhwal <vikram.garhwal@xxxxxxx>
---
 xen/common/Makefile          |   1 +
 xen/common/dt_overlay.c      | 411 +++++++++++++++++++++++++++++++++++
 xen/common/sysctl.c          |   5 +
 xen/include/public/sysctl.h  |  19 ++
 xen/include/xen/dt_overlay.h |  55 +++++
 5 files changed, 491 insertions(+)
 create mode 100644 xen/common/dt_overlay.c
 create mode 100644 xen/include/xen/dt_overlay.h

diff --git a/xen/common/Makefile b/xen/common/Makefile
index 3baf83d527..58a35f55b2 100644
--- a/xen/common/Makefile
+++ b/xen/common/Makefile
@@ -7,6 +7,7 @@ obj-$(CONFIG_DEBUG_TRACE) += debugtrace.o
 obj-$(CONFIG_HAS_DEVICE_TREE) += device_tree.o
 obj-$(CONFIG_IOREQ_SERVER) += dm.o
 obj-y += domain.o
+obj-$(CONFIG_OVERLAY_DTB) += dt_overlay.o
 obj-y += event_2l.o
 obj-y += event_channel.o
 obj-y += event_fifo.o
diff --git a/xen/common/dt_overlay.c b/xen/common/dt_overlay.c
new file mode 100644
index 0000000000..477341f0aa
--- /dev/null
+++ b/xen/common/dt_overlay.c
@@ -0,0 +1,411 @@
+/*
+ * xen/common/dt_overlay.c
+ *
+ * Device tree overlay support in Xen.
+ *
+ * Copyright (c) 2022 AMD Inc.
+ * Written by Vikram Garhwal <vikram.garhwal@xxxxxxx>
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms and conditions of the GNU General Public
+ * License, version 2, as published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ */
+#include <xen/iocap.h>
+#include <xen/xmalloc.h>
+#include <asm/domain_build.h>
+#include <xen/dt_overlay.h>
+#include <xen/guest_access.h>
+
+static LIST_HEAD(overlay_tracker);
+static DEFINE_SPINLOCK(overlay_lock);
+
+/* Find last descendants of the device_node. */
+static struct dt_device_node *find_last_descendants_node(
+                                            struct dt_device_node *device_node)
+{
+    struct dt_device_node *child_node;
+
+    for ( child_node = device_node->child; child_node->sibling != NULL;
+          child_node = child_node->sibling )
+    {
+    }
+
+    /* If last child_node also have children. */
+    if ( child_node->child )
+        child_node = find_last_descendants_node(child_node);
+    return child_node;
+}
+
+static int dt_overlay_remove_node(struct dt_device_node *device_node)
+{
+    struct dt_device_node *np;
+    struct dt_device_node *parent_node;
+    struct dt_device_node *device_node_last_descendant = device_node->child;
+
+    parent_node = device_node->parent;
+
+    if ( parent_node == NULL )
+    {
+        dt_dprintk("%s's parent node not found\n", device_node->name);
+        return -EFAULT;
+    }
+
+    np = parent_node->child;
+
+    if ( np == NULL )
+    {
+        dt_dprintk("parent node %s's not found\n", parent_node->name);
+        return -EFAULT;
+    }
+
+    /* If node to be removed is only child node or first child. */
+    if ( !dt_node_cmp(np->full_name, device_node->full_name) )
+    {
+        parent_node->child = np->sibling;
+
+        /*
+         * Iterate over all child nodes of device_node. Given that we are
+         * removing parent node, we need to remove all it's descendants too.
+         */
+        if ( device_node_last_descendant )
+        {
+            device_node_last_descendant =
+                                        
find_last_descendants_node(device_node);
+            parent_node->allnext = device_node_last_descendant->allnext;
+        }
+        else
+            parent_node->allnext = np->allnext;
+
+        return 0;
+    }
+
+    for ( np = parent_node->child; np->sibling != NULL; np = np->sibling )
+    {
+        if ( !dt_node_cmp(np->sibling->full_name, device_node->full_name) )
+        {
+            /* Found the node. Now we remove it. */
+            np->sibling = np->sibling->sibling;
+
+            if ( np->child )
+                np = find_last_descendants_node(np);
+
+            /*
+             * Iterate over all child nodes of device_node. Given that we are
+             * removing parent node, we need to remove all it's descendants 
too.
+             */
+            if ( device_node_last_descendant )
+                device_node_last_descendant =
+                                        
find_last_descendants_node(device_node);
+
+            if ( device_node_last_descendant )
+                np->allnext = device_node_last_descendant->allnext;
+            else
+                np->allnext = np->allnext->allnext;
+
+            break;
+        }
+    }
+
+    return 0;
+}
+
+/* Basic sanity check for the dtbo tool stack provided to Xen. */
+static int check_overlay_fdt(const void *overlay_fdt, uint32_t 
overlay_fdt_size)
+{
+    if ( (fdt_totalsize(overlay_fdt) != overlay_fdt_size) ||
+          fdt_check_header(overlay_fdt) )
+    {
+        printk(XENLOG_ERR "The overlay FDT is not a valid Flat Device Tree\n");
+        return -EINVAL;
+    }
+
+    return 0;
+}
+
+/* Count number of nodes till one level of __overlay__ tag. */
+static unsigned int overlay_node_count(void *fdto)
+{
+    unsigned int num_overlay_nodes = 0;
+    int fragment;
+
+    fdt_for_each_subnode(fragment, fdto, 0)
+    {
+        int subnode;
+        int overlay;
+
+        overlay = fdt_subnode_offset(fdto, fragment, "__overlay__");
+
+        /*
+         * overlay value can be < 0. But fdt_for_each_subnode() loop checks for
+         * overlay >= 0. So, no need for a overlay>=0 check here.
+         */
+        fdt_for_each_subnode(subnode, fdto, overlay)
+        {
+            num_overlay_nodes++;
+        }
+    }
+
+    return num_overlay_nodes;
+}
+
+static int handle_remove_irq_iommu(struct dt_device_node *device_node)
+{
+    int rc = 0;
+    struct domain *d = hardware_domain;
+    domid_t domid = 0;
+    unsigned int naddr, len;
+    unsigned int i, nirq;
+    u64 addr, size;
+
+    domid = dt_device_used_by(device_node);
+
+    dt_dprintk("Checking if node %s is used by any domain\n",
+               device_node->full_name);
+
+    /* Remove the node iff it's assigned to domain 0 or domain io. */
+    if ( domid != 0 && domid != DOMID_IO )
+    {
+        printk(XENLOG_ERR "Device %s as it is being used by domain %d. 
Removing nodes failed\n",
+               device_node->full_name, domid);
+        return -EINVAL;
+    }
+
+    dt_dprintk("Removing node: %s\n", device_node->full_name);
+
+    nirq = dt_number_of_irq(device_node);
+
+    /* Remove IRQ permission */
+    for ( i = 0; i < nirq; i++ )
+    {
+        rc = platform_get_irq(device_node, i);;
+
+        if ( irq_access_permitted(d, rc) == false )
+        {
+            printk(XENLOG_ERR "IRQ %d is not routed to domain %d\n", rc,
+                   domid);
+            return -EINVAL;
+        }
+        /*
+         * TODO: We don't handle shared IRQs for now. So, it is assumed that
+         * the IRQs was not shared with another devices.
+         */
+        rc = irq_deny_access(d, rc);
+        if ( rc )
+        {
+            printk(XENLOG_ERR "unable to revoke access for irq %u for %s\n",
+                   i, device_node->full_name);
+            return rc;
+        }
+    }
+
+    /* Check if iommu property exists. */
+    if ( dt_get_property(device_node, "iommus", &len) )
+    {
+
+        rc = iommu_remove_dt_device(device_node);
+        if ( rc != 0 && rc != -ENXIO )
+            return rc;
+    }
+
+    naddr = dt_number_of_address(device_node);
+
+    /* Remove mmio access. */
+    for ( i = 0; i < naddr; i++ )
+    {
+        rc = dt_device_get_address(device_node, i, &addr, &size);
+        if ( rc )
+        {
+            printk(XENLOG_ERR "Unable to retrieve address %u for %s\n",
+                   i, dt_node_full_name(device_node));
+            return rc;
+        }
+
+        rc = iomem_deny_access(d, paddr_to_pfn(addr),
+                               paddr_to_pfn(PAGE_ALIGN(addr + size - 1)));
+        if ( rc )
+        {
+            printk(XENLOG_ERR "Unable to remove dom%d access to"
+                   " 0x%"PRIx64" - 0x%"PRIx64"\n",
+                   d->domain_id,
+                   addr & PAGE_MASK, PAGE_ALIGN(addr + size) - 1);
+            return rc;
+        }
+
+    }
+
+    return rc;
+}
+
+/* Removes all descendants of the given node. */
+static int remove_all_descendant_nodes(struct dt_device_node *device_node)
+{
+    int rc = 0;
+    struct dt_device_node *child_node;
+
+    for ( child_node = device_node->child; child_node != NULL;
+         child_node = child_node->sibling )
+    {
+        if ( child_node->child )
+            remove_all_descendant_nodes(child_node);
+
+        rc = handle_remove_irq_iommu(child_node);
+        if ( rc )
+            return rc;
+    }
+
+    return rc;
+}
+
+/* Remove nodes from dt_host. */
+static int remove_nodes(const struct overlay_track *tracker)
+{
+    int rc = 0;
+    struct dt_device_node *overlay_node;
+    unsigned int j;
+
+    for ( j = 0; j < tracker->num_nodes; j++ )
+    {
+        overlay_node = (struct dt_device_node *)tracker->nodes_address[j];
+        if ( overlay_node == NULL )
+        {
+            printk(XENLOG_ERR "Device %s is not present in the tree. Removing 
nodes failed\n",
+                   overlay_node->full_name);
+            return -EINVAL;
+        }
+
+        rc = remove_all_descendant_nodes(overlay_node);
+
+        /* All children nodes are unmapped. Now remove the node itself. */
+        rc = handle_remove_irq_iommu(overlay_node);
+        if ( rc )
+            return rc;
+
+        read_lock(&dt_host->lock);
+
+        rc = dt_overlay_remove_node(overlay_node);
+        if ( rc )
+        {
+            read_unlock(&dt_host->lock);
+
+            return rc;
+        }
+
+        read_unlock(&dt_host->lock);
+    }
+
+    return rc;
+}
+
+/*
+ * First finds the device node to remove. Check if the device is being used by
+ * any dom and finally remove it from dt_host. IOMMU is already being taken 
care
+ * while destroying the domain.
+ */
+static long handle_remove_overlay_nodes(void *overlay_fdt,
+                                        uint32_t overlay_fdt_size)
+{
+    int rc = 0;
+    struct overlay_track *entry, *temp, *track;
+    bool found_entry = false;
+
+    rc = check_overlay_fdt(overlay_fdt, overlay_fdt_size);
+    if ( rc )
+        return rc;
+
+    if ( overlay_node_count(overlay_fdt) == 0 )
+        return -ENOMEM;
+
+    spin_lock(&overlay_lock);
+
+    /*
+     * First check if dtbo is correct i.e. it should one of the dtbo which was
+     * used when dynamically adding the node.
+     * Limitation: Cases with same node names but different property are not
+     * supported currently. We are relying on user to provide the same dtbo
+     * as it was used when adding the nodes.
+     */
+    list_for_each_entry_safe( entry, temp, &overlay_tracker, entry )
+    {
+        if ( memcmp(entry->overlay_fdt, overlay_fdt, overlay_fdt_size) == 0 )
+        {
+            track = entry;
+            found_entry = true;
+            break;
+        }
+    }
+
+    if ( found_entry == false )
+    {
+        rc = -EINVAL;
+
+        printk(XENLOG_ERR "Cannot find any matching tracker with input dtbo."
+               " Removing nodes is supported for only prior added dtbo. Please"
+               " provide a valid dtbo which was used to add the nodes.\n");
+        goto out;
+
+    }
+
+    rc = remove_nodes(entry);
+
+    if ( rc )
+    {
+        printk(XENLOG_ERR "Removing node failed\n");
+        goto out;
+    }
+
+    list_del(&entry->entry);
+
+    xfree(entry->dt_host_new);
+    xfree(entry->fdt);
+    xfree(entry->overlay_fdt);
+
+    xfree(entry->nodes_address);
+
+    xfree(entry);
+
+out:
+    spin_unlock(&overlay_lock);
+    return rc;
+}
+
+long dt_sysctl(struct xen_sysctl_dt_overlay *op)
+{
+    long ret = 0;
+    void *overlay_fdt;
+
+    if ( op->overlay_fdt_size <= 0 || op->overlay_fdt_size > 500000 )
+        return -EINVAL;
+
+    overlay_fdt = xmalloc_bytes(op->overlay_fdt_size);
+
+    if ( overlay_fdt == NULL )
+        return -ENOMEM;
+
+    ret = copy_from_guest(overlay_fdt, op->overlay_fdt, op->overlay_fdt_size);
+    if ( ret )
+    {
+        gprintk(XENLOG_ERR, "copy from guest failed\n");
+        xfree(overlay_fdt);
+
+        return -EFAULT;
+    }
+
+    switch ( op->overlay_op )
+    {
+    case XEN_SYSCTL_DT_OVERLAY_REMOVE:
+        ret = handle_remove_overlay_nodes(overlay_fdt, op->overlay_fdt_size);
+        xfree(overlay_fdt);
+
+        break;
+
+    default:
+        break;
+    }
+
+    return ret;
+}
diff --git a/xen/common/sysctl.c b/xen/common/sysctl.c
index 02505ab044..bb338b7c27 100644
--- a/xen/common/sysctl.c
+++ b/xen/common/sysctl.c
@@ -28,6 +28,7 @@
 #include <xen/pmstat.h>
 #include <xen/livepatch.h>
 #include <xen/coverage.h>
+#include <xen/dt_overlay.h>
 
 long do_sysctl(XEN_GUEST_HANDLE_PARAM(xen_sysctl_t) u_sysctl)
 {
@@ -482,6 +483,10 @@ long do_sysctl(XEN_GUEST_HANDLE_PARAM(xen_sysctl_t) 
u_sysctl)
             copyback = 1;
         break;
 
+    case XEN_SYSCTL_dt_overlay:
+        ret = dt_sysctl(&op->u.dt_overlay);
+        break;
+
     default:
         ret = arch_do_sysctl(op, u_sysctl);
         copyback = 0;
diff --git a/xen/include/public/sysctl.h b/xen/include/public/sysctl.h
index 5672906729..4bc76bbe27 100644
--- a/xen/include/public/sysctl.h
+++ b/xen/include/public/sysctl.h
@@ -1079,6 +1079,23 @@ typedef struct xen_sysctl_cpu_policy 
xen_sysctl_cpu_policy_t;
 DEFINE_XEN_GUEST_HANDLE(xen_sysctl_cpu_policy_t);
 #endif
 
+#define XEN_SYSCTL_DT_OVERLAY_ADD                   1
+#define XEN_SYSCTL_DT_OVERLAY_REMOVE                2
+
+/*
+ * XEN_SYSCTL_dt_overlay
+ * Performs addition/removal of device tree nodes under parent node using dtbo.
+ * This does in three steps:
+ *  - Adds/Removes the nodes from dt_host.
+ *  - Adds/Removes IRQ permission for the nodes.
+ *  - Adds/Removes MMIO accesses.
+ */
+struct xen_sysctl_dt_overlay {
+    XEN_GUEST_HANDLE_64(void) overlay_fdt;
+    uint32_t overlay_fdt_size;  /* Overlay dtb size. */
+    uint8_t overlay_op; /* Add or remove. */
+};
+
 struct xen_sysctl {
     uint32_t cmd;
 #define XEN_SYSCTL_readconsole                    1
@@ -1109,6 +1126,7 @@ struct xen_sysctl {
 #define XEN_SYSCTL_livepatch_op                  27
 /* #define XEN_SYSCTL_set_parameter              28 */
 #define XEN_SYSCTL_get_cpu_policy                29
+#define XEN_SYSCTL_dt_overlay                    30
     uint32_t interface_version; /* XEN_SYSCTL_INTERFACE_VERSION */
     union {
         struct xen_sysctl_readconsole       readconsole;
@@ -1139,6 +1157,7 @@ struct xen_sysctl {
 #if defined(__i386__) || defined(__x86_64__)
         struct xen_sysctl_cpu_policy        cpu_policy;
 #endif
+        struct xen_sysctl_dt_overlay        dt_overlay;
         uint8_t                             pad[128];
     } u;
 };
diff --git a/xen/include/xen/dt_overlay.h b/xen/include/xen/dt_overlay.h
new file mode 100644
index 0000000000..30f4b86586
--- /dev/null
+++ b/xen/include/xen/dt_overlay.h
@@ -0,0 +1,55 @@
+/*
+ * xen/common/dt_overlay.h
+ *
+ * Device tree overlay support in Xen.
+ *
+ * Copyright (c) 2022 AMD Inc.
+ * Written by Vikram Garhwal <vikram.garhwal@xxxxxxx>
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms and conditions of the GNU General Public
+ * License, version 2, as published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ */
+#ifndef __XEN_DT_SYSCTL_H__
+#define __XEN_DT_SYSCTL_H__
+
+#include <xen/list.h>
+#include <xen/libfdt/libfdt.h>
+#include <xen/device_tree.h>
+#include <xen/rangeset.h>
+
+/*
+ * overlay_node_track describes information about added nodes through dtbo.
+ * @entry: List pointer.
+ * @dt_host_new: Pointer to the updated dt_host_new unflattened 'updated fdt'.
+ * @fdt: Stores the fdt.
+ * @nodes_fullname: Stores the full name of nodes.
+ * @nodes_irq: Stores the IRQ added from overlay dtb.
+ * @node_num_irq: Stores num of IRQ for each node in overlay dtb.
+ * @num_nodes: Stores total number of nodes in overlay dtb.
+ */
+struct overlay_track {
+    struct list_head entry;
+    struct dt_device_node *dt_host_new;
+    void *fdt;
+    void *overlay_fdt;
+    unsigned long *nodes_address;
+    unsigned int num_nodes;
+};
+
+struct xen_sysctl_dt_overlay;
+
+#ifdef CONFIG_OVERLAY_DTB
+long dt_sysctl(struct xen_sysctl_dt_overlay *op);
+#else
+static inline long dt_sysctl(struct xen_sysctl_dt_overlay *op)
+{
+    return -ENOSYS;
+}
+#endif
+#endif
-- 
2.17.1