[PATCH v5 5/9] drm/ttm, drm/vmwgfx: Support huge TTM pagefaults

Thomas Hellström (VMware)
2020-03-03T10:23:18Z

Support huge (PMD-size and PUD-size) page-table entries by providing a
huge_fault() callback.
We still support private mappings and write-notify by splitting the huge
page-table entries on write-access.

Note that for huge page-faults to occur, either the kernel needs to be
compiled with trans-huge-pages always enabled, or the kernel needs to be
compiled with trans-huge-pages enabled using madvise, and the user-space
app needs to call madvise() to enable trans-huge pages on a per-mapping
basis.

Furthermore huge page-faults will not succeed unless buffer objects and
user-space addresses are aligned on huge page size boundaries.

Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Michal Hocko <mhocko@suse.com>
Cc: "Matthew Wilcox (Oracle)" <willy@infradead.org>
Cc: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
Cc: Ralph Campbell <rcampbell@nvidia.com>
Cc: "Jérôme Glisse" <jglisse@redhat.com>
Cc: "Christian König" <christian.koenig@amd.com>
Cc: Dan Williams <dan.j.williams@intel.com>
Signed-off-by: Thomas Hellstrom <thellstrom@vmware.com>
Reviewed-by: Roland Scheidegger <sroland@vmware.com>
Reviewed-by: Christian König <christian.koenig@amd.com>
---
drivers/gpu/drm/ttm/ttm_bo_vm.c | 161 ++++++++++++++++++++-
drivers/gpu/drm/vmwgfx/vmwgfx_page_dirty.c | 2 +-
include/drm/ttm/ttm_bo_api.h | 3 +-
3 files changed, 161 insertions(+), 5 deletions(-)

diff --git a/drivers/gpu/drm/ttm/ttm_bo_vm.c b/drivers/gpu/drm/ttm/ttm_bo_vm.c
index 389128b8c4dd..0af14835504c 100644
--- a/drivers/gpu/drm/ttm/ttm_bo_vm.c
+++ b/drivers/gpu/drm/ttm/ttm_bo_vm.c
@@ -156,6 +156,89 @@ vm_fault_t ttm_bo_vm_reserve(struct ttm_buffer_object *bo,
}
EXPORT_SYMBOL(ttm_bo_vm_reserve);

+#ifdef CONFIG_TRANSPARENT_HUGEPAGE
+/**
+ * ttm_bo_vm_insert_huge - Insert a pfn for PUD or PMD faults
+ * @vmf: Fault data
+ * @bo: The buffer object
+ * @page_offset: Page offset from bo start
+ * @fault_page_size: The size of the fault in pages.
+ * @pgprot: The page protections.
+ * Does additional checking whether it's possible to insert a PUD or PMD
+ * pfn and performs the insertion.
+ *
+ * Return: VM_FAULT_NOPAGE on successful insertion, VM_FAULT_FALLBACK if
+ * a huge fault was not possible, or on insertion error.
+ */
+static vm_fault_t ttm_bo_vm_insert_huge(struct vm_fault *vmf,
+ struct ttm_buffer_object *bo,
+ pgoff_t page_offset,
+ pgoff_t fault_page_size,
+ pgprot_t pgprot)
+{
+ pgoff_t i;
+ vm_fault_t ret;
+ unsigned long pfn;
+ pfn_t pfnt;
+ struct ttm_tt *ttm = bo->ttm;
+ bool write = vmf->flags & FAULT_FLAG_WRITE;
+
+ /* Fault should not cross bo boundary. */
+ page_offset &= ~(fault_page_size - 1);
+ if (page_offset + fault_page_size > bo->num_pages)
+ goto out_fallback;
+
+ if (bo->mem.bus.is_iomem)
+ pfn = ttm_bo_io_mem_pfn(bo, page_offset);
+ else
+ pfn = page_to_pfn(ttm->pages[page_offset]);
+
+ /* pfn must be fault_page_size aligned. */
+ if ((pfn & (fault_page_size - 1)) != 0)
+ goto out_fallback;
+
+ /* Check that memory is contiguous. */
+ if (!bo->mem.bus.is_iomem) {
+ for (i = 1; i < fault_page_size; ++i) {
+ if (page_to_pfn(ttm->pages[page_offset + i]) != pfn + i)
+ goto out_fallback;
+ }
+ } else if (bo->bdev->driver->io_mem_pfn) {
+ for (i = 1; i < fault_page_size; ++i) {
+ if (ttm_bo_io_mem_pfn(bo, page_offset + i) != pfn + i)
+ goto out_fallback;
+ }
+ }
+
+ pfnt = __pfn_to_pfn_t(pfn, PFN_DEV);
+ if (fault_page_size == (HPAGE_PMD_SIZE >> PAGE_SHIFT))
+ ret = vmf_insert_pfn_pmd_prot(vmf, pfnt, pgprot, write);
+#ifdef CONFIG_HAVE_ARCH_TRANSPARENT_HUGEPAGE_PUD
+ else if (fault_page_size == (HPAGE_PUD_SIZE >> PAGE_SHIFT))
+ ret = vmf_insert_pfn_pud_prot(vmf, pfnt, pgprot, write);
+#endif
+ else
+ WARN_ON_ONCE(ret = VM_FAULT_FALLBACK);
+
+ if (ret != VM_FAULT_NOPAGE)
+ goto out_fallback;
+
+ return VM_FAULT_NOPAGE;
+out_fallback:
+ count_vm_event(THP_FAULT_FALLBACK);
+ return VM_FAULT_FALLBACK;
+}
+#else
+static vm_fault_t ttm_bo_vm_insert_huge(struct vm_fault *vmf,
+ struct ttm_buffer_object *bo,
+ pgoff_t page_offset,
+ pgoff_t fault_page_size,
+ pgprot_t pgprot)
+{
+ return VM_FAULT_FALLBACK;
+}
+#endif
+
/**
* ttm_bo_vm_fault_reserved - TTM fault helper
* @vmf: The struct vm_fault given as argument to the fault callback
@@ -163,6 +246,7 @@ EXPORT_SYMBOL(ttm_bo_vm_reserve);
* @num_prefault: Maximum number of prefault pages. The caller may want to
* specify this based on madvice settings and the size of the GPU object
* backed by the memory.
+ * @fault_page_size: The size of the fault in pages.
*
* This function inserts one or more page table entries pointing to the
* memory backing the buffer object, and then returns a return code
@@ -176,7 +260,8 @@ EXPORT_SYMBOL(ttm_bo_vm_reserve);
*/
vm_fault_t ttm_bo_vm_fault_reserved(struct vm_fault *vmf,
pgprot_t prot,
- pgoff_t num_prefault)
+ pgoff_t num_prefault,
+ pgoff_t fault_page_size)
{
struct vm_area_struct *vma = vmf->vma;
struct ttm_buffer_object *bo = vma->vm_private_data;
@@ -268,6 +353,13 @@ vm_fault_t ttm_bo_vm_fault_reserved(struct vm_fault *vmf,
prot = pgprot_decrypted(prot);
}

+ /* We don't prefault on huge faults. Yet. */
+ if (IS_ENABLED(CONFIG_TRANSPARENT_HUGEPAGE) && fault_page_size != 1) {
+ ret = ttm_bo_vm_insert_huge(vmf, bo, page_offset,
+ fault_page_size, prot);
+ goto out_io_unlock;
+ }
+
/*
* Speculatively prefault a number of pages. Only error on
* first page.
@@ -334,7 +426,7 @@ vm_fault_t ttm_bo_vm_fault(struct vm_fault *vmf)
return ret;

prot = vma->vm_page_prot;
- ret = ttm_bo_vm_fault_reserved(vmf, prot, TTM_BO_VM_NUM_PREFAULT);
+ ret = ttm_bo_vm_fault_reserved(vmf, prot, TTM_BO_VM_NUM_PREFAULT, 1);
if (ret == VM_FAULT_RETRY && !(vmf->flags & FAULT_FLAG_RETRY_NOWAIT))
return ret;

@@ -344,6 +436,66 @@ vm_fault_t ttm_bo_vm_fault(struct vm_fault *vmf)
}
EXPORT_SYMBOL(ttm_bo_vm_fault);

+#ifdef CONFIG_TRANSPARENT_HUGEPAGE
+/**
+ * ttm_pgprot_is_wrprotecting - Is a page protection value write-protecting?
+ * @prot: The page protection value
+ *
+ * Return: true if @prot is write-protecting. false otherwise.
+ */
+static bool ttm_pgprot_is_wrprotecting(pgprot_t prot)
+{
+ /*
+ * This is meant to say "pgprot_wrprotect(prot) == prot" in a generic
+ * way. Unfortunately there is no generic pgprot_wrprotect.
+ */
+ return pte_val(pte_wrprotect(__pte(pgprot_val(prot)))) ==
+ pgprot_val(prot);
+}
+
+static vm_fault_t ttm_bo_vm_huge_fault(struct vm_fault *vmf,
+ enum page_entry_size pe_size)
+{
+ struct vm_area_struct *vma = vmf->vma;
+ pgprot_t prot;
+ struct ttm_buffer_object *bo = vma->vm_private_data;
+ vm_fault_t ret;
+ pgoff_t fault_page_size = 0;
+ bool write = vmf->flags & FAULT_FLAG_WRITE;
+
+ switch (pe_size) {
+ case PE_SIZE_PMD:
+ fault_page_size = HPAGE_PMD_SIZE >> PAGE_SHIFT;
+ break;
+#ifdef CONFIG_HAVE_ARCH_TRANSPARENT_HUGEPAGE_PUD
+ case PE_SIZE_PUD:
+ fault_page_size = HPAGE_PUD_SIZE >> PAGE_SHIFT;
+ break;
+#endif
+ default:
+ WARN_ON_ONCE(1);
+ return VM_FAULT_FALLBACK;
+ }
+
+ /* Fallback on write dirty-tracking or COW */
+ if (write && ttm_pgprot_is_wrprotecting(vma->vm_page_prot))
+ return VM_FAULT_FALLBACK;
+
+ ret = ttm_bo_vm_reserve(bo, vmf);
+ if (ret)
+ return ret;
+
+ prot = vm_get_page_prot(vma->vm_flags);
+ ret = ttm_bo_vm_fault_reserved(vmf, prot, 1, fault_page_size);
+ if (ret == VM_FAULT_RETRY && !(vmf->flags & FAULT_FLAG_RETRY_NOWAIT))
+ return ret;
+
+ dma_resv_unlock(bo->base.resv);
+
+ return ret;
+}
+#endif
+
void ttm_bo_vm_open(struct vm_area_struct *vma)
{
struct ttm_buffer_object *bo = vma->vm_private_data;
@@ -445,7 +597,10 @@ static const struct vm_operations_struct ttm_bo_vm_ops = {
.fault = ttm_bo_vm_fault,
.open = ttm_bo_vm_open,
.close = ttm_bo_vm_close,
- .access = ttm_bo_vm_access
+ .access = ttm_bo_vm_access,
+#ifdef CONFIG_TRANSPARENT_HUGEPAGE
+ .huge_fault = ttm_bo_vm_huge_fault,
+#endif
};

static struct ttm_buffer_object *ttm_bo_vm_lookup(struct ttm_bo_device *bdev,
diff --git a/drivers/gpu/drm/vmwgfx/vmwgfx_page_dirty.c b/drivers/gpu/drm/vmwgfx/vmwgfx_page_dirty.c
index f07aa857587c..17a5dca7b921 100644
--- a/drivers/gpu/drm/vmwgfx/vmwgfx_page_dirty.c
+++ b/drivers/gpu/drm/vmwgfx/vmwgfx_page_dirty.c
@@ -477,7 +477,7 @@ vm_fault_t vmw_bo_vm_fault(struct vm_fault *vmf)
else
prot = vm_get_page_prot(vma->vm_flags);

- ret = ttm_bo_vm_fault_reserved(vmf, prot, num_prefault);
+ ret = ttm_bo_vm_fault_reserved(vmf, prot, num_prefault, 1);
if (ret == VM_FAULT_RETRY && !(vmf->flags & FAULT_FLAG_RETRY_NOWAIT))
return ret;

diff --git a/include/drm/ttm/ttm_bo_api.h b/include/drm/ttm/ttm_bo_api.h
index 66ca49db9633..4fc90d53aa15 100644
--- a/include/drm/ttm/ttm_bo_api.h
+++ b/include/drm/ttm/ttm_bo_api.h
@@ -732,7 +732,8 @@ vm_fault_t ttm_bo_vm_reserve(struct ttm_buffer_object *bo,

vm_fault_t ttm_bo_vm_fault_reserved(struct vm_fault *vmf,
pgprot_t prot,
- pgoff_t num_prefault);
+ pgoff_t num_prefault,
+ pgoff_t fault_page_size);

vm_fault_t ttm_bo_vm_fault(struct vm_fault *vmf);

--
2.21.1