[PATCH] mm/hmm: fault non-owner device private entries

[PATCH] mm/hmm: fault non-owner device private entries

[Ralph Campbell]

If hmm_range_fault() is called with the HMM_PFN_REQ_FAULT flag and a
device private PTE is found, the hmm_range::dev_private_owner page is
used to determine if the device private page should not be faulted in.
However, if the device private page is not owned by the caller,
hmm_range_fault() returns an error instead of calling migrate_to_ram()
to fault in the page.

Cc: stable@vger.kernel.org
Fixes: 76612d6ce4cc ("mm/hmm: reorganize how !pte_present is handled in hmm_vma_handle_pte()")
Signed-off-by: Ralph Campbell <rcampbell@nvidia.com>
Reported-by: Felix Kuehling <felix.kuehling@amd.com>
---
 mm/hmm.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/mm/hmm.c b/mm/hmm.c
index 3fd3242c5e50..7db2b29bdc85 100644
--- a/mm/hmm.c
+++ b/mm/hmm.c
@@ -273,6 +273,9 @@ static int hmm_vma_handle_pte(struct mm_walk *walk, unsigned long addr,
 		if (!non_swap_entry(entry))
 			goto fault;
 
+		if (is_device_private_entry(entry))
+			goto fault;
+
 		if (is_device_exclusive_entry(entry))
 			goto fault;
 
-- 
2.35.3

Re: [PATCH] mm/hmm: fault non-owner device private entries

[Jason Gunthorpe]

On Fri, Jul 22, 2022 at 03:56:32PM -0700, Ralph Campbell wrote:
> If hmm_range_fault() is called with the HMM_PFN_REQ_FAULT flag and a
> device private PTE is found, the hmm_range::dev_private_owner page is
> used to determine if the device private page should not be faulted in.
> However, if the device private page is not owned by the caller,
> hmm_range_fault() returns an error instead of calling migrate_to_ram()
> to fault in the page.
> 
> Cc: stable@vger.kernel.org
> Fixes: 76612d6ce4cc ("mm/hmm: reorganize how !pte_present is handled in hmm_vma_handle_pte()")
> Signed-off-by: Ralph Campbell <rcampbell@nvidia.com>
> Reported-by: Felix Kuehling <felix.kuehling@amd.com>
> ---
>  mm/hmm.c | 3 +++
>  1 file changed, 3 insertions(+)

Should we have a test for this ?

Reviewed-by: Jason Gunthorpe <jgg@nvidia.com>

Jason

Re: [PATCH] mm/hmm: fault non-owner device private entries

[Alistair Popple]

Ralph Campbell <rcampbell@nvidia.com> writes:

> If hmm_range_fault() is called with the HMM_PFN_REQ_FAULT flag and a
> device private PTE is found, the hmm_range::dev_private_owner page is
> used to determine if the device private page should not be faulted in.
> However, if the device private page is not owned by the caller,
> hmm_range_fault() returns an error instead of calling migrate_to_ram()
> to fault in the page.

		/*
		 * Never fault in device private pages, but just report
		 * the PFN even if not present.
		 */

This comment needs updating because it will be possible to fault in
device private pages now.

It also looks a bit strange to be checking for device private entries
twice - I think it would be clearer if hmm_is_device_private_entry() is
removed and the ownership check done directly in hmm_vma_handle_pte().

 - Alistair

> Cc: stable@vger.kernel.org
> Fixes: 76612d6ce4cc ("mm/hmm: reorganize how !pte_present is handled in hmm_vma_handle_pte()")
> Signed-off-by: Ralph Campbell <rcampbell@nvidia.com>
> Reported-by: Felix Kuehling <felix.kuehling@amd.com>
> ---
>  mm/hmm.c | 3 +++
>  1 file changed, 3 insertions(+)
>
> diff --git a/mm/hmm.c b/mm/hmm.c
> index 3fd3242c5e50..7db2b29bdc85 100644
> --- a/mm/hmm.c
> +++ b/mm/hmm.c
> @@ -273,6 +273,9 @@ static int hmm_vma_handle_pte(struct mm_walk *walk, unsigned long addr,
>  		if (!non_swap_entry(entry))
>  			goto fault;
>
> +		if (is_device_private_entry(entry))
> +			goto fault;
> +
>  		if (is_device_exclusive_entry(entry))
>  			goto fault;

Re: [PATCH] mm/hmm: fault non-owner device private entries

[Felix Kuehling]

Am 2022-07-22 um 18:56 schrieb Ralph Campbell:
> If hmm_range_fault() is called with the HMM_PFN_REQ_FAULT flag and a
> device private PTE is found, the hmm_range::dev_private_owner page is
> used to determine if the device private page should not be faulted in.
> However, if the device private page is not owned by the caller,
> hmm_range_fault() returns an error instead of calling migrate_to_ram()
> to fault in the page.
>
> Cc: stable@vger.kernel.org
> Fixes: 76612d6ce4cc ("mm/hmm: reorganize how !pte_present is handled in hmm_vma_handle_pte()")
> Signed-off-by: Ralph Campbell <rcampbell@nvidia.com>
> Reported-by: Felix Kuehling <felix.kuehling@amd.com>

Acked-by: Felix Kuehling <Felix.Kuehling@amd.com>

Thank you!


> ---
>   mm/hmm.c | 3 +++
>   1 file changed, 3 insertions(+)
>
> diff --git a/mm/hmm.c b/mm/hmm.c
> index 3fd3242c5e50..7db2b29bdc85 100644
> --- a/mm/hmm.c
> +++ b/mm/hmm.c
> @@ -273,6 +273,9 @@ static int hmm_vma_handle_pte(struct mm_walk *walk, unsigned long addr,
>   		if (!non_swap_entry(entry))
>   			goto fault;
>   
> +		if (is_device_private_entry(entry))
> +			goto fault;
> +
>   		if (is_device_exclusive_entry(entry))
>   			goto fault;
>   

Re: [PATCH] mm/hmm: fault non-owner device private entries

[Ralph Campbell]

On 7/23/22 06:32, Jason Gunthorpe wrote:
> On Fri, Jul 22, 2022 at 03:56:32PM -0700, Ralph Campbell wrote:
>> If hmm_range_fault() is called with the HMM_PFN_REQ_FAULT flag and a
>> device private PTE is found, the hmm_range::dev_private_owner page is
>> used to determine if the device private page should not be faulted in.
>> However, if the device private page is not owned by the caller,
>> hmm_range_fault() returns an error instead of calling migrate_to_ram()
>> to fault in the page.
>>
>> Cc: stable@vger.kernel.org
>> Fixes: 76612d6ce4cc ("mm/hmm: reorganize how !pte_present is handled in hmm_vma_handle_pte()")
>> Signed-off-by: Ralph Campbell <rcampbell@nvidia.com>
>> Reported-by: Felix Kuehling <felix.kuehling@amd.com>
>> ---
>>   mm/hmm.c | 3 +++
>>   1 file changed, 3 insertions(+)
> Should we have a test for this ?
>
> Reviewed-by: Jason Gunthorpe <jgg@nvidia.com>
>
> Jason

Sure, I'll add something to tools/testing/selftests/vm/hmm-tests.c

Re: [PATCH] mm/hmm: fault non-owner device private entries

[Ralph Campbell]

On 7/25/22 02:32, Alistair Popple wrote:
> Ralph Campbell <rcampbell@nvidia.com> writes:
>
>> If hmm_range_fault() is called with the HMM_PFN_REQ_FAULT flag and a
>> device private PTE is found, the hmm_range::dev_private_owner page is
>> used to determine if the device private page should not be faulted in.
>> However, if the device private page is not owned by the caller,
>> hmm_range_fault() returns an error instead of calling migrate_to_ram()
>> to fault in the page.
> 		/*
> 		 * Never fault in device private pages, but just report
> 		 * the PFN even if not present.
> 		 */
>
> This comment needs updating because it will be possible to fault in
> device private pages now.
>
> It also looks a bit strange to be checking for device private entries
> twice - I think it would be clearer if hmm_is_device_private_entry() is
> removed and the ownership check done directly in hmm_vma_handle_pte().
>
>   - Alistair

I'll fix this in v2. Thanks for the review.

Re: [PATCH] mm/hmm: fault non-owner device private entries

[Andrew Morton]

On Fri, 22 Jul 2022 15:56:32 -0700 Ralph Campbell <rcampbell@nvidia.com> wrote:

> If hmm_range_fault() is called with the HMM_PFN_REQ_FAULT flag and a
> device private PTE is found, the hmm_range::dev_private_owner page is
> used to determine if the device private page should not be faulted in.
> However, if the device private page is not owned by the caller,
> hmm_range_fault() returns an error instead of calling migrate_to_ram()
> to fault in the page.

Could we please include here a description of the end-user visible
effects of the bug?

> Cc: stable@vger.kernel.org

Especially when proposing a -stable backport.

Re: [PATCH] mm/hmm: fault non-owner device private entries

[Ralph Campbell]

On 7/25/22 11:49, Andrew Morton wrote:
> On Fri, 22 Jul 2022 15:56:32 -0700 Ralph Campbell <rcampbell@nvidia.com> wrote:
>
>> If hmm_range_fault() is called with the HMM_PFN_REQ_FAULT flag and a
>> device private PTE is found, the hmm_range::dev_private_owner page is
>> used to determine if the device private page should not be faulted in.
>> However, if the device private page is not owned by the caller,
>> hmm_range_fault() returns an error instead of calling migrate_to_ram()
>> to fault in the page.
> Could we please include here a description of the end-user visible
> effects of the bug?
>
>> Cc: stable@vger.kernel.org
> Especially when proposing a -stable backport.

If I add the following, would that be sufficient?
Should I post a v3?

For example, if a page is migrated to GPU private
memory and a RDMA fault capable NIC tries to read the migrated page,
without this patch it will get an error. With this patch, the page will
be migrated back to system memory and the NIC will be able to read the
data.

Re: [PATCH] mm/hmm: fault non-owner device private entries

[Andrew Morton]

On Mon, 25 Jul 2022 12:07:27 -0700 Ralph Campbell <rcampbell@nvidia.com> wrote:

> >> to fault in the page.
> > Could we please include here a description of the end-user visible
> > effects of the bug?
> >
> >> Cc: stable@vger.kernel.org
> > Especially when proposing a -stable backport.
> 
> If I add the following, would that be sufficient?
> Should I post a v3?
> 
> For example, if a page is migrated to GPU private
> memory and a RDMA fault capable NIC tries to read the migrated page,
> without this patch it will get an error. With this patch, the page will
> be migrated back to system memory and the NIC will be able to read the
> data.

I added it, thanks.