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drm/amdkfd: avoid recursive lock in migrations back to RAM

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[ Upstream commit a6283010e2907a5576f96b839e1a1c82659f137c ]

[Why]:
When we call hmm_range_fault to map memory after a migration, we don't
expect memory to be migrated again as a result of hmm_range_fault. The
driver ensures that all memory is in GPU-accessible locations so that
no migration should be needed. However, there is one corner case where
hmm_range_fault can unexpectedly cause a migration from DEVICE_PRIVATE
back to system memory due to a write-fault when a system memory page in
the same range was mapped read-only (e.g. COW). Ranges with individual
pages in different locations are usually the result of failed page
migrations (e.g. page lock contention). The unexpected migration back
to system memory causes a deadlock from recursive locking in our
driver.

[How]:
Creating a task reference new member under svm_range_list struct.
Setting this with "current" reference, right before the hmm_range_fault
is called. This member is checked against "current" reference at
svm_migrate_to_ram callback function. If equal, the migration will be
ignored.

Signed-off-by: Alex Sierra <alex.sierra@amd.com>
Reviewed-by: Felix Kuehling <Felix.Kuehling@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Stable-dep-of: 5b994354af3c ("drm/amdkfd: Fix NULL pointer dereference in svm_migrate_to_ram()")
Signed-off-by: Sasha Levin <sashal@kernel.org>
This commit is contained in:
Alex Sierra 2021-10-29 13:30:40 -05:00 committed by Greg Kroah-Hartman
parent 93a5de7e88
commit 36770c045a
3 changed files with 8 additions and 0 deletions
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5
drivers/gpu/drm/amd/amdkfd/kfd_migrate.c
View File

@ -796,6 +796,11 @@ static vm_fault_t svm_migrate_to_ram(struct vm_fault *vmf)
pr_debug("failed find process at fault address 0x%lx\n", addr);
return VM_FAULT_SIGBUS;
}
if (READ_ONCE(p->svms.faulting_task) == current) {
pr_debug("skipping ram migration\n");
kfd_unref_process(p);
return 0;
}
addr >>= PAGE_SHIFT;
pr_debug("CPU page fault svms 0x%p address 0x%lx\n", &p->svms, addr);

1
drivers/gpu/drm/amd/amdkfd/kfd_priv.h
View File

@ -755,6 +755,7 @@ struct svm_range_list {
atomic_t evicted_ranges;
struct delayed_work restore_work;
DECLARE_BITMAP(bitmap_supported, MAX_GPU_INSTANCE);
struct task_struct *faulting_task;
};
/* Process data */

2
drivers/gpu/drm/amd/amdkfd/kfd_svm.c
View File

@ -1489,9 +1489,11 @@ static int svm_range_validate_and_map(struct mm_struct *mm,
next = min(vma->vm_end, end);
npages = (next - addr) >> PAGE_SHIFT;
WRITE_ONCE(p->svms.faulting_task, current);
r = amdgpu_hmm_range_get_pages(&prange->notifier, mm, NULL,
addr, npages, &hmm_range,
readonly, true, owner);
WRITE_ONCE(p->svms.faulting_task, NULL);
if (r) {
pr_debug("failed %d to get svm range pages\n", r);
goto unreserve_out;