switch_to_super_page() assumes the memory range it's working on is aligned to the target large page level. Unfortunately, __domain_mapping() doesn't take this into account when using it, and will pass unaligned ranges ultimately freeing a PTE range larger than expected.
Take for example a mapping with the following iov_pfn range [0x3fe400, 0x4c0600], which should be backed by the following mappings:
iov_pfn [0x3fe400, 0x3fffff] covered by 2MiB pages iov_pfn [0x400000, 0x4bffff] covered by 1GiB pages iov_pfn [0x4c0000, 0x4c05ff] covered by 2MiB pages
Under this circumstance, __domain_mapping() will pass [0x400000, 0x4c05ff] to switch_to_super_page() at a 1 GiB granularity, which will in turn free PTEs all the way to iov_pfn 0x4fffff.
Mitigate this by rounding down the iov_pfn range passed to switch_to_super_page() in __domain_mapping() to the target large page level.
Additionally add range alignment checks to switch_to_super_page.
Fixes: 9906b9352a35 ("iommu/vt-d: Avoid duplicate removing in __domain_mapping()") Signed-off-by: Eugene Koira eugkoira@amazon.com Cc: stable@vger.kernel.org --- drivers/iommu/intel/iommu.c | 7 ++++++- 1 file changed, 6 insertions(+), 1 deletion(-)
diff --git a/drivers/iommu/intel/iommu.c b/drivers/iommu/intel/iommu.c index 9c3ab9d9f69a..dff2d895b8ab 100644 --- a/drivers/iommu/intel/iommu.c +++ b/drivers/iommu/intel/iommu.c @@ -1575,6 +1575,10 @@ static void switch_to_super_page(struct dmar_domain *domain, unsigned long lvl_pages = lvl_to_nr_pages(level); struct dma_pte *pte = NULL;
+ if (WARN_ON(!IS_ALIGNED(start_pfn, lvl_pages) || + !IS_ALIGNED(end_pfn + 1, lvl_pages))) + return; + while (start_pfn <= end_pfn) { if (!pte) pte = pfn_to_dma_pte(domain, start_pfn, &level, @@ -1650,7 +1654,8 @@ __domain_mapping(struct dmar_domain *domain, unsigned long iov_pfn, unsigned long pages_to_remove;
pteval |= DMA_PTE_LARGE_PAGE; - pages_to_remove = min_t(unsigned long, nr_pages, + pages_to_remove = min_t(unsigned long, + round_down(nr_pages, lvl_pages), nr_pte_to_next_page(pte) * lvl_pages); end_pfn = iov_pfn + pages_to_remove - 1; switch_to_super_page(domain, iov_pfn, end_pfn, largepage_lvl);
On Tue Aug 26, 2025 at 2:38 PM UTC, Eugene Koira wrote:
switch_to_super_page() assumes the memory range it's working on is aligned to the target large page level. Unfortunately, __domain_mapping() doesn't take this into account when using it, and will pass unaligned ranges ultimately freeing a PTE range larger than expected.
Take for example a mapping with the following iov_pfn range [0x3fe400, 0x4c0600], which should be backed by the following mappings:
iov_pfn [0x3fe400, 0x3fffff] covered by 2MiB pages iov_pfn [0x400000, 0x4bffff] covered by 1GiB pages iov_pfn [0x4c0000, 0x4c05ff] covered by 2MiB pages
Under this circumstance, __domain_mapping() will pass [0x400000, 0x4c05ff] to switch_to_super_page() at a 1 GiB granularity, which will in turn free PTEs all the way to iov_pfn 0x4fffff.
Mitigate this by rounding down the iov_pfn range passed to switch_to_super_page() in __domain_mapping() to the target large page level.
Additionally add range alignment checks to switch_to_super_page.
Fixes: 9906b9352a35 ("iommu/vt-d: Avoid duplicate removing in __domain_mapping()") Signed-off-by: Eugene Koira eugkoira@amazon.com Cc: stable@vger.kernel.org
drivers/iommu/intel/iommu.c | 7 ++++++- 1 file changed, 6 insertions(+), 1 deletion(-)
diff --git a/drivers/iommu/intel/iommu.c b/drivers/iommu/intel/iommu.c index 9c3ab9d9f69a..dff2d895b8ab 100644 --- a/drivers/iommu/intel/iommu.c +++ b/drivers/iommu/intel/iommu.c @@ -1575,6 +1575,10 @@ static void switch_to_super_page(struct dmar_domain *domain, unsigned long lvl_pages = lvl_to_nr_pages(level); struct dma_pte *pte = NULL;
- if (WARN_ON(!IS_ALIGNED(start_pfn, lvl_pages) ||
!IS_ALIGNED(end_pfn + 1, lvl_pages)))
It might make sense to downgrade the warning to WARN_ON_ONCE().
Other than that:
Reviewed-by: Nicolas Saenz Julienne nsaenz@amazon.com
Regards, Nicolas
On Tue, 2025-08-26 at 14:38 +0000, Eugene Koira wrote:
switch_to_super_page() assumes the memory range it's working on is aligned to the target large page level. Unfortunately, __domain_mapping() doesn't take this into account when using it, and will pass unaligned ranges ultimately freeing a PTE range larger than expected.
Take for example a mapping with the following iov_pfn range [0x3fe400, 0x4c0600], which should be backed by the following mappings:
The range is [0x3fe400, 0x4c0600) ?
iov_pfn [0x3fe400, 0x3fffff] covered by 2MiB pages iov_pfn [0x400000, 0x4bffff] covered by 1GiB pages iov_pfn [0x4c0000, 0x4c05ff] covered by 2MiB pages
Under this circumstance, __domain_mapping() will pass [0x400000, 0x4c05ff] to switch_to_super_page() at a 1 GiB granularity, which will in turn free PTEs all the way to iov_pfn 0x4fffff.
Mitigate this by rounding down the iov_pfn range passed to switch_to_super_page() in __domain_mapping() to the target large page level.
Additionally add range alignment checks to switch_to_super_page.
Fixes: 9906b9352a35 ("iommu/vt-d: Avoid duplicate removing in __domain_mapping()") Signed-off-by: Eugene Koira eugkoira@amazon.com Cc: stable@vger.kernel.org
drivers/iommu/intel/iommu.c | 7 ++++++- 1 file changed, 6 insertions(+), 1 deletion(-)
diff --git a/drivers/iommu/intel/iommu.c b/drivers/iommu/intel/iommu.c index 9c3ab9d9f69a..dff2d895b8ab 100644 --- a/drivers/iommu/intel/iommu.c +++ b/drivers/iommu/intel/iommu.c @@ -1575,6 +1575,10 @@ static void switch_to_super_page(struct dmar_domain *domain, unsigned long lvl_pages = lvl_to_nr_pages(level); struct dma_pte *pte = NULL;
- if (WARN_ON(!IS_ALIGNED(start_pfn, lvl_pages) ||
!IS_ALIGNED(end_pfn + 1, lvl_pages)))return;while (start_pfn <= end_pfn) { if (!pte) pte = pfn_to_dma_pte(domain, start_pfn, &level, @@ -1650,7 +1654,8 @@ __domain_mapping(struct dmar_domain *domain, unsigned long iov_pfn, unsigned long pages_to_remove; pteval |= DMA_PTE_LARGE_PAGE;
pages_to_remove = min_t(unsigned long, nr_pages,
pages_to_remove = min_t(unsigned long,round_down(nr_pages, lvl_pages),nr_pte_to_next_page(pte) * lvl_pages); end_pfn = iov_pfn + pages_to_remove - 1; switch_to_super_page(domain, iov_pfn, end_pfn, largepage_lvl);
I'm mildly entertained by the fact that the *only* comment in this block of code is a lie. Would you care to address that while you're here? Maybe the comment could look something like...
/* If the new mapping is eligible for a large page, then * remove all smaller pages that the existing pte at this * level references. * XX: do we even need to bother calling switch_to_super_page() * if this PTE wasn't *present* before? */
I bet it would benefit from one or two other one-line comments to make it clearer what's going on, too...
But in general, I think this looks sane even though this code makes my brain hurt. Could do with a test case, in an ideal world. Maybe we can work on that as part of the generic pagetable support which is coming?
linux-stable-mirror@lists.linaro.org
-
David Woodhouse -
Eugene Koira -
Nicolas Saenz Julienne