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[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [PATCH v2] xen: don't require virtio with grants for non-PV guests
On 16.06.22 11:56, Juergen Gross wrote: Hello Juergen, all On 16.06.22 09:31, Oleksandr wrote:On 16.06.22 08:37, Juergen Gross wrote: Hello Juergen okPlease note, I am happy with current patch and it works in my Arm64 based environment. Just one moment to consider.As it was already mentioned earlier in current thread the PLATFORM_VIRTIO_RESTRICTED_MEM_ACCESS (former arch_has_restricted_virtio_memory_access()) is not per device but about the whole guest. Being set it makes VIRTIO_F_ACCESS_PLATFORM and VIRTIO_F_VERSION_1 features mandatory for *all* virtio devices in the guest. The question is “Do we want/need to lift this restriction for some devices (which backends are trusted so can access all guest memory) at the same time”? Copy here the original Viresh's question for the convenience: "I understand from your email that the backends need to offer the VIRTIO_F_ACCESS_PLATFORM flag now, but should this requirement be a bit soft? I mean shouldn't we allow both types of backends to run with the same kernel, ones that offer this feature and others that don't? The ones that don't offer the feature, should continue to work like they used to, i.e. without the restricted memory access feature." Technically this can be possible with HVM. Let's imagine the following situation: - Dom0 with backends which don't offer required features for some reason(s)But running in Dom0 (trusted domain) these backends are not obliged to offer it (yes they can offer the required features and support grant mappings for the virtio, but this is not strictly necessary, as they are considered as trusted so are allowed to access all guest memory). - DomD with backend which do offer them and require grant mappings for the virtio If this is a valid and correct use-case, then we indeed need an ability to control that per device, otherwise - what is written below doesn't really matter. I am wondering whether we can avoid using global PLATFORM_VIRTIO_RESTRICTED_MEM_ACCESS for Xen guests at all? I assume that all we need to do (when CONFIG_XEN_VIRTIO is enabled) is to make sure that *only* Xen grant DMA devices in HVM guests and *all* devices in PV guests offer required flags. Below the diff how this could be done w/o an extra options (not completely tested), although I realize it might look hackish, and a lot more effort is needed to get it right. In my Arm64 based environment it works, I have tried to run two backends, the first offered required features and the corresponding device node had required property, but the second didn’t and there was no property. diff --git a/arch/arm/xen/enlighten.c b/arch/arm/xen/enlighten.c index 1f9c3ba..07eb69f 100644 --- a/arch/arm/xen/enlighten.c +++ b/arch/arm/xen/enlighten.c @@ -443,8 +443,6 @@ static int __init xen_guest_init(void) if (!xen_domain()) return 0; - xen_set_restricted_virtio_memory_access(); - if (!acpi_disabled) xen_acpi_guest_init(); else diff --git a/arch/x86/xen/enlighten_hvm.c b/arch/x86/xen/enlighten_hvm.c index 8b71b1d..517a9d8 100644 --- a/arch/x86/xen/enlighten_hvm.c +++ b/arch/x86/xen/enlighten_hvm.c @@ -195,8 +195,6 @@ static void __init xen_hvm_guest_init(void) if (xen_pv_domain()) return; - xen_set_restricted_virtio_memory_access(); - init_hvm_pv_info(); reserve_shared_info(); diff --git a/arch/x86/xen/enlighten_pv.c b/arch/x86/xen/enlighten_pv.c index 30d24fe..ca85d14 100644 --- a/arch/x86/xen/enlighten_pv.c +++ b/arch/x86/xen/enlighten_pv.c@@ -108,8 +108,6 @@ static DEFINE_PER_CPU(struct tls_descs, shadow_tls_desc);
static void __init xen_pv_init_platform(void)
{
- xen_set_restricted_virtio_memory_access();
-
populate_extra_pte(fix_to_virt(FIX_PARAVIRT_BOOTMAP));
set_fixmap(FIX_PARAVIRT_BOOTMAP, xen_start_info->shared_info);
diff --git a/drivers/virtio/virtio.c b/drivers/virtio/virtio.c
index 371e16b..875690a 100644
--- a/drivers/virtio/virtio.c
+++ b/drivers/virtio/virtio.c
@@ -167,6 +167,11 @@ void virtio_add_status(struct virtio_device *dev,
unsigned int status)
}
EXPORT_SYMBOL_GPL(virtio_add_status);
+int __weak device_has_restricted_virtio_memory_access(struct device *dev)
+{
+ return platform_has(PLATFORM_VIRTIO_RESTRICTED_MEM_ACCESS);
+}
+
/* Do some validation, then set FEATURES_OK */
static int virtio_features_ok(struct virtio_device *dev)
{
@@ -174,7 +179,7 @@ static int virtio_features_ok(struct virtio_device *dev)
might_sleep();
- if (platform_has(PLATFORM_VIRTIO_RESTRICTED_MEM_ACCESS)) {
+ if (device_has_restricted_virtio_memory_access(dev->dev.parent)) {
if (!virtio_has_feature(dev, VIRTIO_F_VERSION_1)) {
dev_warn(&dev->dev,
"device must provide
VIRTIO_F_VERSION_1\n");
diff --git a/drivers/xen/grant-dma-ops.c b/drivers/xen/grant-dma-ops.c
index 6586152..da938f6 100644
--- a/drivers/xen/grant-dma-ops.c
+++ b/drivers/xen/grant-dma-ops.c
@@ -11,6 +11,7 @@
#include <linux/dma-map-ops.h>
#include <linux/of.h>
#include <linux/pfn.h>
+#include <linux/virtio_config.h>
#include <linux/xarray.h>
#include <xen/xen.h>
#include <xen/grant_table.h>
@@ -286,6 +287,11 @@ bool xen_is_grant_dma_device(struct device *dev)
return has_iommu;
}
+int device_has_restricted_virtio_memory_access(struct device *dev)
+{
+ return (xen_pv_domain() || xen_is_grant_dma_device(dev));
+}
+
void xen_grant_setup_dma_ops(struct device *dev)
{
struct xen_grant_dma_data *data;
diff --git a/include/linux/virtio_config.h b/include/linux/virtio_config.h
index 7949829..b3a455b 100644
--- a/include/linux/virtio_config.h
+++ b/include/linux/virtio_config.h
@@ -559,4 +559,6 @@ static inline void virtio_cwrite64(struct
virtio_device *vdev,
_r; \ }) +int device_has_restricted_virtio_memory_access(struct device *dev); + #endif /* _LINUX_VIRTIO_CONFIG_H */ diff --git a/include/xen/xen.h b/include/xen/xen.h index 0780a81..a99bab8 100644 --- a/include/xen/xen.h +++ b/include/xen/xen.h@@ -52,14 +52,6 @@ bool xen_biovec_phys_mergeable(const struct bio_vec *vec1,
extern u64 xen_saved_max_mem_size;
#endif
-#include <linux/platform-feature.h>
-
-static inline void xen_set_restricted_virtio_memory_access(void)
-{
- if (IS_ENABLED(CONFIG_XEN_VIRTIO) && xen_domain())
- platform_set(PLATFORM_VIRTIO_RESTRICTED_MEM_ACCESS);
-}
-
#ifdef CONFIG_XEN_UNPOPULATED_ALLOC
int xen_alloc_unpopulated_pages(unsigned int nr_pages, struct page
**pages);
void xen_free_unpopulated_pages(unsigned int nr_pages, struct page
**pages);
(END)I think when x86 HVM gains required support (via ACPI or other means) to communicate the x86's alternative of "xen,grant-dma" then xen_is_grant_dma_device() will be just extended to handle that.
bool xen_is_grant_dma_device(struct device *dev)
{
struct device_node *iommu_np;
bool has_iommu;
/* XXX Handle only DT devices for now */
if (!dev->of_node)
return false;
iommu_np = of_parse_phandle(dev->of_node, "iommus", 0);
has_iommu = iommu_np && of_device_is_compatible(iommu_np,
"xen,grant-dma");
of_node_put(iommu_np); return has_iommu; } Juergen -- Regards, Oleksandr Tyshchenko
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