On 28/02/2025 10:44, Thomas Hellström wrote:
The pnfs that we obtain from hmm_range_fault() point to pages that
we don't have a reference on, and the guarantee that they are still
in the cpu page-tables is that the notifier lock must be held and the
notifier seqno is still valid.
So while building the sg table and marking the pages accesses / dirty
we need to hold this lock with a validated seqno.
However, the lock is reclaim tainted which makes
sg_alloc_table_from_pages_segment() unusable, since it internally
allocates memory.
Instead build the sg-table manually. For the non-iommu case
this might lead to fewer coalesces, but if that's a problem it can
be fixed up later in the resource cursor code. For the iommu case,
the whole sg-table may still be coalesced to a single contigous
device va region.
This avoids marking pages that we don't own dirty and accessed, and
it also avoid dereferencing struct pages that we don't own.
Fixes: 81e058a3e7fd ("drm/xe: Introduce helper to populate userptr")
Cc: Oak Zeng <oak.zeng@xxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx> # v6.10+
Signed-off-by: Thomas Hellström <thomas.hellstrom@xxxxxxxxxxxxxxx>
---
drivers/gpu/drm/xe/xe_hmm.c | 115 ++++++++++++++++++++++++++----------
1 file changed, 85 insertions(+), 30 deletions(-)
diff --git a/drivers/gpu/drm/xe/xe_hmm.c b/drivers/gpu/drm/xe/xe_hmm.c
index c56738fa713b..d3b5551496d0 100644
--- a/drivers/gpu/drm/xe/xe_hmm.c
+++ b/drivers/gpu/drm/xe/xe_hmm.c
@@ -42,6 +42,36 @@ static void xe_mark_range_accessed(struct hmm_range *range, bool write)
}
}
+static int xe_alloc_sg(struct sg_table *st, struct hmm_range *range,
+ struct rw_semaphore *notifier_sem)
+{
+ unsigned long i, npages, hmm_pfn;
+ unsigned long num_chunks = 0;
+ int ret;
+
+ /* HMM docs says this is needed. */
+ ret = down_read_interruptible(notifier_sem);
+ if (ret)
+ return ret;
+
+ if (mmu_interval_read_retry(range->notifier, range->notifier_seq))
+ return -EAGAIN;
+
+ npages = xe_npages_in_range(range->start, range->end);
+ for (i = 0; i < npages;) {
+ hmm_pfn = range->hmm_pfns[i];
+ if (!(hmm_pfn & HMM_PFN_VALID)) {
Is this possible? The default_flags are always REQ_FAULT, so that should
ensure PFN_VALID, or the hmm_fault would have returned an error?
From the docs:
"HMM_PFN_REQ_FAULT - The output must have HMM_PFN_VALID or
hmm_range_fault() will fail"
Should this be an assert?
Also probably dumb question, but why do we need to hold the notifier
lock over this loop? What is it protecting?
+ up_read(notifier_sem);
+ return -EFAULT;
+ }
+ num_chunks++;
+ i += 1UL << hmm_pfn_to_map_order(hmm_pfn);
+ }
+ up_read(notifier_sem);
+
+ return sg_alloc_table(st, num_chunks, GFP_KERNEL);
+}
+
/**
* xe_build_sg() - build a scatter gather table for all the physical pages/pfn
* in a hmm_range. dma-map pages if necessary. dma-address is save in sg table
@@ -50,6 +80,7 @@ static void xe_mark_range_accessed(struct hmm_range *range, bool write)
* @range: the hmm range that we build the sg table from. range->hmm_pfns[]
* has the pfn numbers of pages that back up this hmm address range.
* @st: pointer to the sg table.
+ * @notifier_sem: The xe notifier lock.
* @write: whether we write to this range. This decides dma map direction
* for system pages. If write we map it bi-diretional; otherwise
* DMA_TO_DEVICE
@@ -76,38 +107,33 @@ static void xe_mark_range_accessed(struct hmm_range *range, bool write)
* Returns 0 if successful; -ENOMEM if fails to allocate memory
*/
static int xe_build_sg(struct xe_device *xe, struct hmm_range *range,
- struct sg_table *st, bool write)
+ struct sg_table *st,
+ struct rw_semaphore *notifier_sem,
+ bool write)
{
struct device *dev = xe->drm.dev;
- struct page **pages;
- u64 i, npages;
- int ret;
-
- npages = xe_npages_in_range(range->start, range->end);
- pages = kvmalloc_array(npages, sizeof(*pages), GFP_KERNEL);
- if (!pages)
- return -ENOMEM;
-
- for (i = 0; i < npages; i++) {
- pages[i] = hmm_pfn_to_page(range->hmm_pfns[i]);
- xe_assert(xe, !is_device_private_page(pages[i]));
- }
-
- ret = sg_alloc_table_from_pages_segment(st, pages, npages, 0, npages << PAGE_SHIFT,
- xe_sg_segment_size(dev), GFP_KERNEL);
- if (ret)
- goto free_pages;
-
- ret = dma_map_sgtable(dev, st, write ? DMA_BIDIRECTIONAL : DMA_TO_DEVICE,
- DMA_ATTR_SKIP_CPU_SYNC | DMA_ATTR_NO_KERNEL_MAPPING);
- if (ret) {
- sg_free_table(st);
- st = NULL;
+ unsigned long hmm_pfn, size;
+ struct scatterlist *sgl;
+ struct page *page;
+ unsigned long i, j;
+
+ lockdep_assert_held(notifier_sem);
+
+ i = 0;
+ for_each_sg(st->sgl, sgl, st->nents, j) {
+ hmm_pfn = range->hmm_pfns[i];
+ page = hmm_pfn_to_page(hmm_pfn);
+ xe_assert(xe, !is_device_private_page(page));
+ size = 1UL << hmm_pfn_to_map_order(hmm_pfn);
+ sg_set_page(sgl, page, size << PAGE_SHIFT, 0);
+ if (unlikely(j == st->nents - 1))
+ sg_mark_end(sgl);
+ i += size;
}
+ xe_assert(xe, i == xe_npages_in_range(range->start, range->end));
-free_pages:
- kvfree(pages);
- return ret;
+ return dma_map_sgtable(dev, st, write ? DMA_BIDIRECTIONAL : DMA_TO_DEVICE,
+ DMA_ATTR_SKIP_CPU_SYNC | DMA_ATTR_NO_KERNEL_MAPPING);
}
/**
@@ -235,16 +261,45 @@ int xe_hmm_userptr_populate_range(struct xe_userptr_vma *uvma,
if (ret)
goto free_pfns;
- ret = xe_build_sg(vm->xe, &hmm_range, &userptr->sgt, write);
+ if (unlikely(userptr->sg)) {
+ ret = down_write_killable(&vm->userptr.notifier_lock);
+ if (ret)
+ goto free_pfns;
+
+ xe_hmm_userptr_free_sg(uvma);
+ up_write(&vm->userptr.notifier_lock);
+ }
+
+ ret = xe_alloc_sg(&userptr->sgt, &hmm_range, &vm->userptr.notifier_lock);
if (ret)
goto free_pfns;
+ ret = down_read_interruptible(&vm->userptr.notifier_lock);
+ if (ret)
+ goto free_st;
+
+ if (mmu_interval_read_retry(hmm_range.notifier, hmm_range.notifier_seq)) {
+ ret = -EAGAIN;
+ goto out_unlock;
+ }
+
+ ret = xe_build_sg(vm->xe, &hmm_range, &userptr->sgt,
+ &vm->userptr.notifier_lock, write);
+ if (ret)
+ goto out_unlock;
+
xe_mark_range_accessed(&hmm_range, write);
userptr->sg = &userptr->sgt;
userptr->notifier_seq = hmm_range.notifier_seq;
+ up_read(&vm->userptr.notifier_lock);
+ kvfree(pfns);
+ return 0;
+out_unlock:
+ up_read(&vm->userptr.notifier_lock);
+free_st:
+ sg_free_table(&userptr->sgt);
free_pfns:
kvfree(pfns);
return ret;
}
-
