netdev - [PATCH] vhost: fix caching attributes of MMIO regions by setting them explicitly

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Message-ID: <20260102065703.656255-1-kshankar@marvell.com>
Date: Fri, 2 Jan 2026 12:27:03 +0530
From: Kommula Shiva Shankar <kshankar@...vell.com>
To: <mst@...hat.com>
CC: <jasowang@...hat.com>, <virtualization@...ts.linux.dev>,
        <eperezma@...hat.com>, <kvm@...r.kernel.org>, <netdev@...r.kernel.org>,
        <jerinj@...vell.com>, <ndabilpuram@...vell.com>, <schalla@...vell.com>
Subject: [PATCH] vhost: fix caching attributes of MMIO regions by setting them explicitly

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@...vell.com>
Acked-by: Jason Wang <jasowang@...hat.com>
---
Originally sent to net-next, now redirected to vhost tree
per Jason Wang's suggestion. 

 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