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.

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.

Cc: stable@vger.kernel.org Fixes: 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 Reviewed-by: Alistair Popple apopple@nvidia.com Cc: Philip Yang Philip.Yang@amd.com Cc: Alistair Popple apopple@nvidia.com Cc: Jason Gunthorpe jgg@nvidia.com Cc: stable@vger.kernel.org Signed-off-by: Andrew Morton akpm@linux-foundation.org --- 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;