Re: [PATCH v2 1/2] mm/hmm: fault non-owner device private entries

[Alistair Popple <apopple@nvidia.com>]

Thanks Ralph, please add:

Reviewed-by: Alistair Popple <apopple@nvidia.com>

However I think the fixes tag is wrong, see below.

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.
>
> Cc: stable@vger.kernel.org
> Fixes: 76612d6ce4cc ("mm/hmm: reorganize how !pte_present is handled in hmm_vma_handle_pte()")

This should be 08ddddda667b ("mm/hmm: check the device private page owner in hmm_range_fault()")

> Signed-off-by: Ralph Campbell <rcampbell@nvidia.com>
> Reported-by: Felix Kuehling <felix.kuehling@amd.com>
> ---
>  mm/hmm.c | 19 ++++++++-----------
>  1 file changed, 8 insertions(+), 11 deletions(-)
>
> diff --git a/mm/hmm.c b/mm/hmm.c
> index 3fd3242c5e50..f2aa63b94d9b 100644
> --- a/mm/hmm.c
> +++ b/mm/hmm.c
> @@ -212,14 +212,6 @@ int hmm_vma_handle_pmd(struct mm_walk *walk, unsigned long addr,
>  		unsigned long end, unsigned long hmm_pfns[], pmd_t pmd);
>  #endif /* CONFIG_TRANSPARENT_HUGEPAGE */
>
> -static inline bool hmm_is_device_private_entry(struct hmm_range *range,
> -		swp_entry_t entry)
> -{
> -	return is_device_private_entry(entry) &&
> -		pfn_swap_entry_to_page(entry)->pgmap->owner ==
> -		range->dev_private_owner;
> -}
> -
>  static inline unsigned long pte_to_hmm_pfn_flags(struct hmm_range *range,
>  						 pte_t pte)
>  {
> @@ -252,10 +244,12 @@ static int hmm_vma_handle_pte(struct mm_walk *walk, unsigned long addr,
>  		swp_entry_t entry = pte_to_swp_entry(pte);
>
>  		/*
> -		 * Never fault in device private pages, but just report
> -		 * the PFN even if not present.
> +		 * Don't fault in device private pages owned by the caller,
> +		 * just report the PFN.
>  		 */
> -		if (hmm_is_device_private_entry(range, entry)) {
> +		if (is_device_private_entry(entry) &&
> +		    pfn_swap_entry_to_page(entry)->pgmap->owner ==
> +		    range->dev_private_owner) {
>  			cpu_flags = HMM_PFN_VALID;
>  			if (is_writable_device_private_entry(entry))
>  				cpu_flags |= HMM_PFN_WRITE;
> @@ -273,6 +267,9 @@ 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;