The patch titled
Subject: mm/hmm: fault non-owner device private entries
has been added to the -mm mm-hotfixes-unstable branch. Its filename is
mm-hmm-fault-non-owner-device-private-entries.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-hmm-fault-non-owner-device-private-entries.patch
This patch will later appear in the mm-hotfixes-unstable branch at
git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
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------------------------------------------------------
From: Ralph Campbell <rcampbell@xxxxxxxxxx>
Subject: mm/hmm: fault non-owner device private entries
Date: Mon, 25 Jul 2022 11:36:14 -0700
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.
Link: https://lkml.kernel.org/r/20220725183615.4118795-2-rcampbell@xxxxxxxxxx
Fixes: 76612d6ce4cc ("mm/hmm: reorganize how !pte_present is handled in hmm_vma_handle_pte()")
Signed-off-by: Ralph Campbell <rcampbell@xxxxxxxxxx>
Reported-by: Felix Kuehling <felix.kuehling@xxxxxxx>
Cc: Philip Yang <Philip.Yang@xxxxxxx>
Cc: Alistair Popple <apopple@xxxxxxxxxx>
Cc: Jason Gunthorpe <jgg@xxxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/hmm.c | 19 ++++++++-----------
1 file changed, 8 insertions(+), 11 deletions(-)
--- a/mm/hmm.c~mm-hmm-fault-non-owner-device-private-entries
+++ a/mm/hmm.c
@@ -212,14 +212,6 @@ int hmm_vma_handle_pmd(struct mm_walk *w
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_
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_
if (!non_swap_entry(entry))
goto fault;
+ if (is_device_private_entry(entry))
+ goto fault;
+
if (is_device_exclusive_entry(entry))
goto fault;
_
Patches currently in -mm which might be from rcampbell@xxxxxxxxxx are
mm-hmm-fault-non-owner-device-private-entries.patch
mm-hmm-add-a-test-for-cross-device-private-faults.patch
