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Re: [RFC PATCH 4/6] virtio: Various updates to xen-virtio DMA ops layer




Hello Stefano, Juergen


On 19.04.22 09:58, Juergen Gross wrote:
On 18.04.22 21:11, Stefano Stabellini wrote:
On Sun, 17 Apr 2022, Oleksandr wrote:
On 16.04.22 01:02, Stefano Stabellini wrote:
On Thu, 14 Apr 2022, Oleksandr Tyshchenko wrote:
From: Oleksandr Tyshchenko <oleksandr_tyshchenko@xxxxxxxx>

In the context of current patch do the following:
1. Update code to support virtio-mmio devices
2. Introduce struct xen_virtio_data and account passed virtio devices
     (using list) as we need to store some per-device data
3. Add multi-page support for xen_virtio_dma_map(unmap)_page callbacks
4. Harden code against malicious backend
5. Change to use alloc_pages_exact() instead of __get_free_pages()
6. Introduce locking scheme to protect mappings (I am not 100% sure
     whether per-device lock is really needed)
7. Handle virtio device's DMA mask
8. Retrieve the ID of backend domain from DT for virtio-mmio device
     instead of hardcoding it.

Signed-off-by: Oleksandr Tyshchenko <oleksandr_tyshchenko@xxxxxxxx>
---
   arch/arm/xen/enlighten.c |  11 +++
   drivers/xen/Kconfig      |   2 +-
   drivers/xen/xen-virtio.c | 200
++++++++++++++++++++++++++++++++++++++++++-----
   include/xen/xen-ops.h    |   5 ++
   4 files changed, 196 insertions(+), 22 deletions(-)

diff --git a/arch/arm/xen/enlighten.c b/arch/arm/xen/enlighten.c
index ec5b082..870d92f 100644
--- a/arch/arm/xen/enlighten.c
+++ b/arch/arm/xen/enlighten.c
@@ -409,6 +409,17 @@ int __init arch_xen_unpopulated_init(struct resource
**res)
   }
   #endif
   +#ifdef CONFIG_ARCH_HAS_RESTRICTED_VIRTIO_MEMORY_ACCESS
+int arch_has_restricted_virtio_memory_access(void)
+{
+    if (IS_ENABLED(CONFIG_XEN_HVM_VIRTIO_GRANT) && xen_hvm_domain())
+        return 1;
Instead of xen_hvm_domain(), you can just use xen_domain(). Also there
is no need for the #ifdef
CONFIG_ARCH_HAS_RESTRICTED_VIRTIO_MEMORY_ACCESS, given that:

CONFIG_XEN_HVM_VIRTIO_GRANT depends on XEN_VIRTIO which selects
ARCH_HAS_RESTRICTED_VIRTIO_MEMORY_ACCESS


Yes, but please see my comments in commit #2 regarding
CONFIG_XEN_HVM_VIRTIO_GRANT option and
arch_has_restricted_virtio_memory_access() on Arm.

I propose to have the following on Arm:

int arch_has_restricted_virtio_memory_access(void)
{
      return xen_has_restricted_virtio_memory_access();
}


where common xen.h contain a helper to be used by both Arm and x86:

static inline int xen_has_restricted_virtio_memory_access(void)
{
      if (IS_ENABLED(CONFIG_XEN_VIRTIO) && (xen_pv_domain() ||
xen_hvm_domain()))
          return 1;

      return 0;
}


But I would be happy with what you propose as well.

As I wrote in the previous reply, I also prefer to share the code
between x86 and ARM, and I think it could look like:

int arch_has_restricted_virtio_memory_access(void)
{
      return xen_has_restricted_virtio_memory_access();
}
[...]
static inline int xen_has_restricted_virtio_memory_access(void)
{
      return (IS_ENABLED(CONFIG_XEN_VIRTIO) && xen_domain());
}

But let's check with Juergen and Boris.


for the record, it is already clarified in commit #2, I will use this variant.





+    return 0;
+}
+EXPORT_SYMBOL_GPL(arch_has_restricted_virtio_memory_access);
+#endif
+
   static void __init xen_dt_guest_init(void)
   {
       struct device_node *xen_node;
diff --git a/drivers/xen/Kconfig b/drivers/xen/Kconfig
index fc61f7a..56afe6a 100644
--- a/drivers/xen/Kconfig
+++ b/drivers/xen/Kconfig
@@ -347,7 +347,7 @@ config XEN_VIRTIO
     config XEN_HVM_VIRTIO_GRANT
       bool "Require virtio for fully virtualized guests to use grant
mappings"
-    depends on XEN_VIRTIO && X86_64
+    depends on XEN_VIRTIO && (X86_64 || ARM || ARM64)
you can remove the architectural dependencies


According to the conversation in commit #2 we are considering just a single
XEN_VIRTIO option, but it is going to has the
same architectural dependencies: (X86_64 || ARM || ARM64)

By removing the architectural dependencies here, we will leave also X86_32 covered (neither XEN_HVM_VIRTIO_GRANT nor XEN_PV_VIRTIO covered it). I don't
know whether it is ok or not.

Shall I remove dependencies anyway?

No, good point. I don't know about X86_32. This is another detail where
Juergen or Boris should comment.

X86_32 should in theory work (it is HVM/PVH only, as PV 32-bit guests are no
longer supported).


ok, thank you for confirming. I will drop architectural dependencies then.





Juergen

--
Regards,

Oleksandr Tyshchenko




 


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