[PATCH net-next ] vdpa: fix caching attributes of MMIO regions by setting them explicitly

[PATCH net-next ] vdpa: fix caching attributes of MMIO regions by setting them explicitly

[Kommula Shiva Shankar]

Explicitly set non-cached caching attributes for MMIO regions.
Default write-back mode can cause CPU to cache device memory,
causing invalid reads and unpredictable behavior.

Invalid read and write issues were observed on ARM64 when mapping the
notification area to userspace via mmap.

Signed-off-by: Kommula Shiva Shankar <kshankar@marvell.com>
---
 drivers/vhost/vdpa.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/drivers/vhost/vdpa.c b/drivers/vhost/vdpa.c
index 05a481e4c385..b0179e8567ab 100644
--- a/drivers/vhost/vdpa.c
+++ b/drivers/vhost/vdpa.c
@@ -1527,6 +1527,7 @@ static int vhost_vdpa_mmap(struct file *file, struct vm_area_struct *vma)
 	if (vma->vm_end - vma->vm_start != notify.size)
 		return -ENOTSUPP;
 
+	vma->vm_page_prot = pgprot_noncached(vma->vm_page_prot);
 	vm_flags_set(vma, VM_IO | VM_PFNMAP | VM_DONTEXPAND | VM_DONTDUMP);
 	vma->vm_ops = &vhost_vdpa_vm_ops;
 	return 0;
-- 
2.48.1

Re: [PATCH net-next ] vdpa: fix caching attributes of MMIO regions by setting them explicitly

[Jason Wang]

On Wed, Dec 17, 2025 at 1:59 AM Kommula Shiva Shankar
<kshankar@marvell.com> wrote:
>
> Explicitly set non-cached caching attributes for MMIO regions.
> Default write-back mode can cause CPU to cache device memory,
> causing invalid reads and unpredictable behavior.
>
> Invalid read and write issues were observed on ARM64 when mapping the
> notification area to userspace via mmap.
>
> Signed-off-by: Kommula Shiva Shankar <kshankar@marvell.com>
> ---

Acked-by: Jason Wang <jasowang@redhat.com>

Btw, I think this should go with Michael's vhost tree.

Thanks

Re: [PATCH net-next ] vdpa: fix caching attributes of MMIO regions by setting them explicitly

[Paolo Abeni]

On 12/16/25 6:59 PM, Kommula Shiva Shankar wrote:
> Explicitly set non-cached caching attributes for MMIO regions.
> Default write-back mode can cause CPU to cache device memory,
> causing invalid reads and unpredictable behavior.
> 
> Invalid read and write issues were observed on ARM64 when mapping the
> notification area to userspace via mmap.
> 
> Signed-off-by: Kommula Shiva Shankar <kshankar@marvell.com>

@Micheal: despite the net-next prefix, I assume this patch will go via
your tree, as it looks unrelated from networking.

Cheers,

Paolo