[PATCH 0/2] iommu/vt-d: Fixes for v5.16-rc3

[PATCH 0/2] iommu/vt-d: Fixes for v5.16-rc3

[Lu Baolu]

Hi Joerg,

Two small fixes are queued for v5.16. They aim to fix:

 - Unbalanced rcu_read_lock/unlock() in cap_audit_static();
 - Missed unmapped PTE entries in dma_pte_clear_level().

This series is also available on github:
https://github.com/LuBaolu/intel-iommu/commits/vtd-fix-for-v5.16-rc3

Please consider them for the iommu/fix branch.

Best regards,
Lu Baolu

Alex Williamson (1):
  iommu/vt-d: Fix unmap_pages support

Christophe JAILLET (1):
  iommu/vt-d: Fix an unbalanced rcu_read_lock/rcu_read_unlock()

 drivers/iommu/intel/cap_audit.c | 5 +++--
 drivers/iommu/intel/iommu.c     | 2 +-
 2 files changed, 4 insertions(+), 3 deletions(-)

-- 
2.25.1

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[PATCH 1/2] iommu/vt-d: Fix an unbalanced rcu_read_lock/rcu_read_unlock()

[Lu Baolu]

From: Christophe JAILLET <christophe.jaillet@wanadoo.fr>

If we return -EOPNOTSUPP, the rcu lock remains lock. This is spurious.
Go through the end of the function instead. This way, the missing
'rcu_read_unlock()' is called.

Fixes: 7afd7f6aa21a ("iommu/vt-d: Check FL and SL capability sanity in scalable mode")
Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
Link: https://lore.kernel.org/r/40cc077ca5f543614eab2a10e84d29dd190273f6.1636217517.git.christophe.jaillet@wanadoo.fr
Signed-off-by: Lu Baolu <baolu.lu@linux.intel.com>
---
 drivers/iommu/intel/cap_audit.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/drivers/iommu/intel/cap_audit.c b/drivers/iommu/intel/cap_audit.c
index b39d223926a4..71596fc62822 100644
--- a/drivers/iommu/intel/cap_audit.c
+++ b/drivers/iommu/intel/cap_audit.c
@@ -144,6 +144,7 @@ static int cap_audit_static(struct intel_iommu *iommu, enum cap_audit_type type)
 {
 	struct dmar_drhd_unit *d;
 	struct intel_iommu *i;
+	int rc = 0;
 
 	rcu_read_lock();
 	if (list_empty(&dmar_drhd_units))
@@ -169,11 +170,11 @@ static int cap_audit_static(struct intel_iommu *iommu, enum cap_audit_type type)
 	 */
 	if (intel_cap_smts_sanity() &&
 	    !intel_cap_flts_sanity() && !intel_cap_slts_sanity())
-		return -EOPNOTSUPP;
+		rc = -EOPNOTSUPP;
 
 out:
 	rcu_read_unlock();
-	return 0;
+	return rc;
 }
 
 int intel_cap_audit(enum cap_audit_type type, struct intel_iommu *iommu)
-- 
2.25.1

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[PATCH 2/2] iommu/vt-d: Fix unmap_pages support

[Lu Baolu]

From: Alex Williamson <alex.williamson@redhat.com>

When supporting only the .map and .unmap callbacks of iommu_ops,
the IOMMU driver can make assumptions about the size and alignment
used for mappings based on the driver provided pgsize_bitmap.  VT-d
previously used essentially PAGE_MASK for this bitmap as any power
of two mapping was acceptably filled by native page sizes.

However, with the .map_pages and .unmap_pages interface we're now
getting page-size and count arguments.  If we simply combine these
as (page-size * count) and make use of the previous map/unmap
functions internally, any size and alignment assumptions are very
different.

As an example, a given vfio device assignment VM will often create
a 4MB mapping at IOVA pfn [0x3fe00 - 0x401ff].  On a system that
does not support IOMMU super pages, the unmap_pages interface will
ask to unmap 1024 4KB pages at the base IOVA.  dma_pte_clear_level()
will recurse down to level 2 of the page table where the first half
of the pfn range exactly matches the entire pte level.  We clear the
pte, increment the pfn by the level size, but (oops) the next pte is
on a new page, so we exit the loop an pop back up a level.  When we
then update the pfn based on that higher level, we seem to assume
that the previous pfn value was at the start of the level.  In this
case the level size is 256K pfns, which we add to the base pfn and
get a results of 0x7fe00, which is clearly greater than 0x401ff,
so we're done.  Meanwhile we never cleared the ptes for the remainder
of the range.  When the VM remaps this range, we're overwriting valid
ptes and the VT-d driver complains loudly, as reported by the user
report linked below.

The fix for this seems relatively simple, if each iteration of the
loop in dma_pte_clear_level() is assumed to clear to the end of the
level pte page, then our next pfn should be calculated from level_pfn
rather than our working pfn.

Fixes: 3f34f1259776 ("iommu/vt-d: Implement map/unmap_pages() iommu_ops callback")
Reported-by: Ajay Garg <ajaygargnsit@gmail.com>
Signed-off-by: Alex Williamson <alex.williamson@redhat.com>
Tested-by: Giovanni Cabiddu <giovanni.cabiddu@intel.com>
Link: https://lore.kernel.org/all/20211002124012.18186-1-ajaygargnsit@gmail.com/
Link: https://lore.kernel.org/r/163659074748.1617923.12716161410774184024.stgit@omen
Signed-off-by: Lu Baolu <baolu.lu@linux.intel.com>
---
 drivers/iommu/intel/iommu.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/iommu/intel/iommu.c b/drivers/iommu/intel/iommu.c
index 0bde0c8b4126..8ed3fc3b11d6 100644
--- a/drivers/iommu/intel/iommu.c
+++ b/drivers/iommu/intel/iommu.c
@@ -1366,7 +1366,7 @@ static struct page *dma_pte_clear_level(struct dmar_domain *domain, int level,
 						       freelist);
 		}
 next:
-		pfn += level_size(level);
+		pfn = level_pfn + level_size(level);
 	} while (!first_pte_in_page(++pte) && pfn <= last_pfn);
 
 	if (first_pte)
-- 
2.25.1

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Re: [PATCH 2/2] iommu/vt-d: Fix unmap_pages support

[Lu Baolu]

On 2021/11/22 11:24, Lu Baolu wrote:
> From: Alex Williamson<alex.williamson@redhat.com>
> 
> When supporting only the .map and .unmap callbacks of iommu_ops,
> the IOMMU driver can make assumptions about the size and alignment
> used for mappings based on the driver provided pgsize_bitmap.  VT-d
> previously used essentially PAGE_MASK for this bitmap as any power
> of two mapping was acceptably filled by native page sizes.
> 
> However, with the .map_pages and .unmap_pages interface we're now
> getting page-size and count arguments.  If we simply combine these
> as (page-size * count) and make use of the previous map/unmap
> functions internally, any size and alignment assumptions are very
> different.
> 
> As an example, a given vfio device assignment VM will often create
> a 4MB mapping at IOVA pfn [0x3fe00 - 0x401ff].  On a system that
> does not support IOMMU super pages, the unmap_pages interface will
> ask to unmap 1024 4KB pages at the base IOVA.  dma_pte_clear_level()
> will recurse down to level 2 of the page table where the first half
> of the pfn range exactly matches the entire pte level.  We clear the
> pte, increment the pfn by the level size, but (oops) the next pte is
> on a new page, so we exit the loop an pop back up a level.  When we
> then update the pfn based on that higher level, we seem to assume
> that the previous pfn value was at the start of the level.  In this
> case the level size is 256K pfns, which we add to the base pfn and
> get a results of 0x7fe00, which is clearly greater than 0x401ff,
> so we're done.  Meanwhile we never cleared the ptes for the remainder
> of the range.  When the VM remaps this range, we're overwriting valid
> ptes and the VT-d driver complains loudly, as reported by the user
> report linked below.
> 
> The fix for this seems relatively simple, if each iteration of the
> loop in dma_pte_clear_level() is assumed to clear to the end of the
> level pte page, then our next pfn should be calculated from level_pfn
> rather than our working pfn.
> 
> Fixes: 3f34f1259776 ("iommu/vt-d: Implement map/unmap_pages() iommu_ops callback")
> Reported-by: Ajay Garg<ajaygargnsit@gmail.com>
> Signed-off-by: Alex Williamson<alex.williamson@redhat.com>
> Tested-by: Giovanni Cabiddu<giovanni.cabiddu@intel.com>
> Link:https://lore.kernel.org/all/20211002124012.18186-1-ajaygargnsit@gmail.com/
> Link:https://lore.kernel.org/r/163659074748.1617923.12716161410774184024.stgit@omen
> Signed-off-by: Lu Baolu<baolu.lu@linux.intel.com>

0-day build robot reported an error on this patch.

"drivers/iommu/intel/iommu.c:1344:7: warning: variable 'level_pfn' is 
used uninitialized whenever 'if' condition is true 
[-Wsometimes-uninitialized]
"

I will send a v2 of this patch. Sorry for the inconvenience.

Best regards
baolu
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Re: [PATCH 0/2] iommu/vt-d: Fixes for v5.16-rc3

[Joerg Roedel]

On Mon, Nov 22, 2021 at 11:24:56AM +0800, Lu Baolu wrote:
> Alex Williamson (1):
>   iommu/vt-d: Fix unmap_pages support
> 
> Christophe JAILLET (1):
>   iommu/vt-d: Fix an unbalanced rcu_read_lock/rcu_read_unlock()

Queued for v5.16, thanks.
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