[PATCH] iommu/amd: Only unmap large pages from the first pte

[PATCH] iommu/amd: Only unmap large pages from the first pte

[Alex Williamson]

If we use a large mapping, the expectation is that only unmaps from
the first pte in the superpage are supported.  Unmaps from offsets
into the superpage should fail (ie. return zero sized unmap).  In the
current code, unmapping from an offset clears the size of the full
mapping starting from an offset.  For instance, if we map a 16k
physically contiguous range at IOVA 0x0 with a large page, then
attempt to unmap 4k at offset 12k, 4 ptes are cleared (12k - 28k) and
the unmap returns 16k unmapped.  This potentially incorrectly clears
valid mappings and confuses drivers like VFIO that use the unmap size
to release pinned pages.

Fix by refusing to unmap from offsets into the page.

Signed-off-by: Alex Williamson <alex.williamson@redhat.com>
Cc: stable@vger.kernel.org
---
 drivers/iommu/amd_iommu.c |    6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/drivers/iommu/amd_iommu.c b/drivers/iommu/amd_iommu.c
index 21d02b0..a3c3389 100644
--- a/drivers/iommu/amd_iommu.c
+++ b/drivers/iommu/amd_iommu.c
@@ -1484,6 +1484,10 @@ static unsigned long iommu_unmap_page(struct protection_domain *dom,
 
 			/* Large PTE found which maps this address */
 			unmap_size = PTE_PAGE_SIZE(*pte);
+
+			/* Only unmap from the first pte in the page */
+			if ((unmap_size - 1) & bus_addr)
+				break;
 			count      = PAGE_SIZE_PTE_COUNT(unmap_size);
 			for (i = 0; i < count; i++)
 				pte[i] = 0ULL;
@@ -1493,7 +1497,7 @@ static unsigned long iommu_unmap_page(struct protection_domain *dom,
 		unmapped += unmap_size;
 	}
 
-	BUG_ON(!is_power_of_2(unmapped));
+	BUG_ON(unmapped && !is_power_of_2(unmapped));
 
 	return unmapped;
 }

Re: [PATCH] iommu/amd: Only unmap large pages from the first pte

[Joerg Roedel]

On Fri, Jun 21, 2013 at 02:33:19PM -0600, Alex Williamson wrote:
> If we use a large mapping, the expectation is that only unmaps from
> the first pte in the superpage are supported.  Unmaps from offsets
> into the superpage should fail (ie. return zero sized unmap).  In the
> current code, unmapping from an offset clears the size of the full
> mapping starting from an offset.  For instance, if we map a 16k
> physically contiguous range at IOVA 0x0 with a large page, then
> attempt to unmap 4k at offset 12k, 4 ptes are cleared (12k - 28k) and
> the unmap returns 16k unmapped.  This potentially incorrectly clears
> valid mappings and confuses drivers like VFIO that use the unmap size
> to release pinned pages.
> 
> Fix by refusing to unmap from offsets into the page.
> 
> Signed-off-by: Alex Williamson <alex.williamson@redhat.com>
> Cc: stable@vger.kernel.org

Applied, thanks for fixing this.