[PATCH] nouveau/vmm: start tracking if the LPT PTE is valid. (v3)

[Dave Airlie <airlied@gmail.com>]

From: Dave Airlie <airlied@redhat.com>

When NVK enabled large pages userspace tests were seeing fault
reports at a valid address.

There was a case where an address moving from 64k page to 4k pages
could expose a race between unmapping the 4k page, mapping the 64k
page and unref the 4k pages.

Unref 4k pages would cause the dual-page table handling to always
set the LPTE entry to SPARSE or INVALID, but if we'd mapped a valid
LPTE in the meantime, it would get trashed. Keep track of when
a valid LPTE has been referenced, and don't reset in that case.

This increase the tracking to 32-bit, because it turns out if
unref can get delayed, you can get a lot of these outstanding
and this can cause strange behaviours.

Cc: stable@vger.kernel.org
Link: https://gitlab.freedesktop.org/mesa/mesa/-/issues/14610
Signed-off-by: Dave Airlie <airlied@redhat.com>

--
v2: move to 32-bit from 8-bit tracker
fix some more flag changes.
v3: missed one BIG_PTE unset
---
 drivers/gpu/drm/nouveau/nvkm/subdev/mmu/vmm.c | 44 ++++++++++++++-----
 drivers/gpu/drm/nouveau/nvkm/subdev/mmu/vmm.h |  9 ++--
 2 files changed, 37 insertions(+), 16 deletions(-)

diff --git a/drivers/gpu/drm/nouveau/nvkm/subdev/mmu/vmm.c b/drivers/gpu/drm/nouveau/nvkm/subdev/mmu/vmm.c
index f95c58b67633..970e5f94a6e3 100644
--- a/drivers/gpu/drm/nouveau/nvkm/subdev/mmu/vmm.c
+++ b/drivers/gpu/drm/nouveau/nvkm/subdev/mmu/vmm.c
@@ -53,7 +53,7 @@ nvkm_vmm_pt_new(const struct nvkm_vmm_desc *desc, bool sparse,
 		}
 	}
 
-	if (!(pgt = kzalloc(sizeof(*pgt) + lpte, GFP_KERNEL)))
+	if (!(pgt = kzalloc(sizeof(*pgt) + (sizeof(pgt->pte[0]) * lpte), GFP_KERNEL)))
 		return NULL;
 	pgt->page = page ? page->shift : 0;
 	pgt->sparse = sparse;
@@ -242,14 +242,17 @@ nvkm_vmm_unref_sptes(struct nvkm_vmm_iter *it, struct nvkm_vmm_pt *pgt,
 		if (pgt->pte[pteb] & NVKM_VMM_PTE_SPARSE) {
 			TRA(it, "LPTE %05x: U -> S %d PTEs", pteb, ptes);
 			pair->func->sparse(vmm, pgt->pt[0], pteb, ptes);
-		} else
-		if (pair->func->invalid) {
-			/* If the MMU supports it, restore the LPTE to the
-			 * INVALID state to tell the MMU there is no point
-			 * trying to fetch the corresponding SPTEs.
-			 */
-			TRA(it, "LPTE %05x: U -> I %d PTEs", pteb, ptes);
-			pair->func->invalid(vmm, pgt->pt[0], pteb, ptes);
+		} else if (!(pgt->pte[pteb] & NVKM_VMM_PTE_BIG_VALID)) {
+			if (pair->func->invalid) {
+				/* If the MMU supports it, restore the LPTE to the
+				 * INVALID state to tell the MMU there is no point
+				 * trying to fetch the corresponding SPTEs.
+				 */
+				TRA(it, "LPTE %05x: U -> I %d PTEs", pteb, ptes);
+				pair->func->invalid(vmm, pgt->pt[0], pteb, ptes);
+			}
+		} else {
+			TRA(it, "LPTE %05x: V %d PTEs", pteb, ptes);
 		}
 	}
 }
@@ -280,6 +283,13 @@ nvkm_vmm_unref_ptes(struct nvkm_vmm_iter *it, bool pfn, u32 ptei, u32 ptes)
 	if (desc->type == SPT && (pgt->refs[0] || pgt->refs[1]))
 		nvkm_vmm_unref_sptes(it, pgt, desc, ptei, ptes);
 
+	if (desc->type == LPT && (pgt->refs[0] || pgt->refs[1])) {
+		for (u32 lpti = ptei; ptes; lpti++) {
+			pgt->pte[lpti] &= ~NVKM_VMM_PTE_BIG_VALID;
+			ptes--;
+		}
+	}
+
 	/* PT no longer needed? Destroy it. */
 	if (!pgt->refs[type]) {
 		it->lvl++;
@@ -332,10 +342,12 @@ nvkm_vmm_ref_sptes(struct nvkm_vmm_iter *it, struct nvkm_vmm_pt *pgt,
 		 * Determine how many LPTEs need to transition state.
 		 */
 		pgt->pte[ptei] |= NVKM_VMM_PTE_VALID;
+		pgt->pte[ptei] &= ~NVKM_VMM_PTE_BIG_VALID;
 		for (ptes = 1, ptei++; ptei < lpti; ptes++, ptei++) {
 			if (pgt->pte[ptei] & NVKM_VMM_PTE_VALID)
 				break;
 			pgt->pte[ptei] |= NVKM_VMM_PTE_VALID;
+			pgt->pte[ptei] &= ~NVKM_VMM_PTE_BIG_VALID;
 		}
 
 		if (pgt->pte[pteb] & NVKM_VMM_PTE_SPARSE) {
@@ -374,6 +386,14 @@ nvkm_vmm_ref_ptes(struct nvkm_vmm_iter *it, bool pfn, u32 ptei, u32 ptes)
 	if (desc->type == SPT)
 		nvkm_vmm_ref_sptes(it, pgt, desc, ptei, ptes);
 
+	if (desc->type == LPT) {
+		for (u32 lpti = ptei; ptes; lpti++) {
+			pgt->pte[lpti] &= ~NVKM_VMM_PTE_VALID;
+			pgt->pte[lpti] |= NVKM_VMM_PTE_BIG_VALID;
+			ptes--;
+		}
+	}
+
 	return true;
 }
 
@@ -386,7 +406,7 @@ nvkm_vmm_sparse_ptes(const struct nvkm_vmm_desc *desc,
 			pgt->pde[ptei++] = NVKM_VMM_PDE_SPARSE;
 	} else
 	if (desc->type == LPT) {
-		memset(&pgt->pte[ptei], NVKM_VMM_PTE_SPARSE, ptes);
+		memset32(&pgt->pte[ptei], NVKM_VMM_PTE_SPARSE, ptes);
 	}
 }
 
@@ -398,7 +418,7 @@ nvkm_vmm_sparse_unref_ptes(struct nvkm_vmm_iter *it, bool pfn, u32 ptei, u32 pte
 		memset(&pt->pde[ptei], 0x00, sizeof(pt->pde[0]) * ptes);
 	else
 	if (it->desc->type == LPT)
-		memset(&pt->pte[ptei], 0x00, sizeof(pt->pte[0]) * ptes);
+		memset32(&pt->pte[ptei], 0x00, ptes);
 	return nvkm_vmm_unref_ptes(it, pfn, ptei, ptes);
 }
 
@@ -457,7 +477,7 @@ nvkm_vmm_ref_hwpt(struct nvkm_vmm_iter *it, struct nvkm_vmm_pt *pgd, u32 pdei)
 					desc->func->sparse(vmm, pt, pteb, ptes);
 				else
 					desc->func->invalid(vmm, pt, pteb, ptes);
-				memset(&pgt->pte[pteb], 0x00, ptes);
+				memset32(&pgt->pte[pteb], 0x00, ptes);
 			} else {
 				desc->func->unmap(vmm, pt, pteb, ptes);
 				while (ptes--)
diff --git a/drivers/gpu/drm/nouveau/nvkm/subdev/mmu/vmm.h b/drivers/gpu/drm/nouveau/nvkm/subdev/mmu/vmm.h
index 4586a425dbe4..3720579f4bf7 100644
--- a/drivers/gpu/drm/nouveau/nvkm/subdev/mmu/vmm.h
+++ b/drivers/gpu/drm/nouveau/nvkm/subdev/mmu/vmm.h
@@ -44,10 +44,11 @@ struct nvkm_vmm_pt {
 	 *
 	 * This information is used to manage LPTE state transitions.
 	 */
-#define NVKM_VMM_PTE_SPARSE 0x80
-#define NVKM_VMM_PTE_VALID  0x40
-#define NVKM_VMM_PTE_SPTES  0x3f
-	u8 pte[];
+#define NVKM_VMM_PTE_SPARSE    0x80000000
+#define NVKM_VMM_PTE_VALID     0x40000000
+#define NVKM_VMM_PTE_BIG_VALID 0x20000000
+#define NVKM_VMM_PTE_SPTES     0x1fffffff
+	u32 pte[];
 };
 
 typedef void (*nvkm_vmm_pxe_func)(struct nvkm_vmm *,
-- 
2.52.0