vhost: fix caching attributes of MMIO regions by setting them explicitly

[ Upstream commit 5145b27 ]

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>
Reviewed-by: Jason Gunthorpe <jgg@nvidia.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Message-Id: <20260102065703.656255-1-kshankar@marvell.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>

Author: ShivaShankarKommula

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;