iommu/intel: Fix __domain_mapping()'s usage of switch_to_super_page()

[PATCH] iommu/intel: Fix __domain_mapping()'s usage of switch_to_super_page()

Posted by Eugene Koira 1 month, 1 week ago

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);
-- 
2.47.3




Amazon Development Center (Netherlands) B.V., Johanna Westerdijkplein 1, NL-2521 EN The Hague, Registration No. Chamber of Commerce 56869649, VAT: NL 852339859B01

Re: [PATCH] iommu/intel: Fix __domain_mapping()'s usage of switch_to_super_page()

Posted by Baolu Lu 1 month ago

On 8/26/25 22:38, 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(-)

Queued for v6.17-rc. Thank you!

Thanks,
baolu

Re: [PATCH] iommu/intel: Fix __domain_mapping()'s usage of switch_to_super_page()

Posted by David Woodhouse 1 month, 1 week ago

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?

Re: [PATCH] iommu/intel: Fix __domain_mapping()'s usage of switch_to_super_page()

Posted by Baolu Lu 1 month ago

On 8/26/25 23:48, David Woodhouse wrote:
> 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?

Agreed. The generic pagetable work will replace this code, so this will
be removed. Therefore, we need a fix patch that can be backported before
the generic pagetable for vt-d lands.

Thanks,
baolu

Re: [PATCH] iommu/intel: Fix __domain_mapping()'s usage of switch_to_super_page()

Posted by David Woodhouse 1 month ago

On Thu, 2025-08-28 at 14:33 +0800, Baolu Lu wrote:
> On 8/26/25 23:48, David Woodhouse wrote:
> > 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?
> 
> Agreed. The generic pagetable work will replace this code, so this will
> be removed. Therefore, we need a fix patch that can be backported before
> the generic pagetable for vt-d lands.

Yep. And since Jason has in fact already posted the patches which
*delete* all this code, I don't think I even care about fixing the
comments. Eugene's patch is fine as-is.

Reviewed-by: David Woodhouse <dwmw@amazon.co.uk>

Re: [PATCH] iommu/intel: Fix __domain_mapping()'s usage of switch_to_super_page()

Posted by Nicolas Saenz Julienne 1 month, 1 week ago

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