FAILED: patch "[PATCH] arm64: tlb: Flush walk cache when unsharing PMD tables" failed to apply to 6.18-stable tree

The patch below does not apply to the 6.18-stable tree.
If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to <[email protected]>.

To reproduce the conflict and resubmit, you may use the following commands:

git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-6.18.y
git checkout FETCH_HEAD
git cherry-pick -x c2ff4764e03e7a8d758352f4aceb8fe1be6ac971
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<[email protected]>' --in-reply-to '2026052832-capitol-implicit-6395@gregkh' --subject-prefix 'PATCH 6.18.y' HEAD^..

Possible dependencies:

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From c2ff4764e03e7a8d758352f4aceb8fe1be6ac971 Mon Sep 17 00:00:00 2001
From: Zeng Heng <[email protected]>
Date: Thu, 21 May 2026 15:30:11 +0800
Subject: [PATCH] arm64: tlb: Flush walk cache when unsharing PMD tables

When huge_pmd_unshare() is called to unshare a PMD table, the tlb_unshare_pmd_ptdesc() function sets tlb->unshared_tables=true but the aarch64 tlb_flush() only checked tlb->freed_tables to determine whether to use TLBF_NONE (vae1is, invalidates walk cache) or TLBF_NOWALKCACHE (vale1is, leaf-only).

This caused the stale PMD page table entry to remain in the walk cache after unshare, potentially leading to incorrect page table walks.

Fix by including unshared_tables in the check, so that when unsharing tables, TLBF_NONE is used and the walk cache is properly invalidated.

Here is the detailed distinction between vae1is and vale1is:

| Instruction Combination  | Actual Invalidation Scope                         |
| ------------------------ | --------------------------------------------------|
| `VAE1IS`  + TTL=`0`      | All entries at all levels (full invalidation)     |
| `VAE1IS`  + TTL=`2` (L2) | Non-leaf at Level 0/1 + leaf at Level 2           |
| `VALE1IS` + TTL=`0`      | Leaf entries at all levels (non-leaf not cleared) |
| `VALE1IS` + TTL=`2` (L2) | Leaf entry at Level 2 only                        |

index 10869d7731b8..751bd57bc3ba 100644
@@ -53,7 +53,8 @@ static inline int tlb_get_level(struct mmu_gather *tlb)
 static inline void tlb_flush(struct mmu_gather *tlb)
 {
 	struct vm_area_struct vma = TLB_FLUSH_VMA(tlb->mm, 0);
-	tlbf_t flags = tlb->freed_tables ? TLBF_NONE : TLBF_NOWALKCACHE;
+	tlbf_t flags = (tlb->freed_tables || tlb->unshared_tables) ?
+			TLBF_NONE : TLBF_NOWALKCACHE;
 	unsigned long stride = tlb_get_unmap_size(tlb);
 	int tlb_level = tlb_get_level(tlb);
 

From: Zeng Heng <[email protected]>

[ Upstream commit c2ff4764e03e7a8d758352f4aceb8fe1be6ac971 ]

When huge_pmd_unshare() is called to unshare a PMD table, the tlb_unshare_pmd_ptdesc() function sets tlb->unshared_tables=true but the aarch64 tlb_flush() only checked tlb->freed_tables to determine whether to use TLBF_NONE (vae1is, invalidates walk cache) or TLBF_NOWALKCACHE (vale1is, leaf-only).

This caused the stale PMD page table entry to remain in the walk cache after unshare, potentially leading to incorrect page table walks.

Fix by including unshared_tables in the check, so that when unsharing tables, TLBF_NONE is used and the walk cache is properly invalidated.

Here is the detailed distinction between vae1is and vale1is:

| Instruction Combination  | Actual Invalidation Scope                         |
| ------------------------ | --------------------------------------------------|
| `VAE1IS`  + TTL=`0`      | All entries at all levels (full invalidation)     |
| `VAE1IS`  + TTL=`2` (L2) | Non-leaf at Level 0/1 + leaf at Level 2           |
| `VALE1IS` + TTL=`0`      | Leaf entries at all levels (non-leaf not cleared) |
| `VALE1IS` + TTL=`2` (L2) | Leaf entry at Level 2 only                        |

---
 arch/arm64/include/asm/tlb.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

index 8d762607285cc..b3b863c919fea 100644
@@ -53,7 +53,7 @@ static inline int tlb_get_level(struct mmu_gather *tlb)
 static inline void tlb_flush(struct mmu_gather *tlb)
 {
 	struct vm_area_struct vma = TLB_FLUSH_VMA(tlb->mm, 0);
-	bool last_level = !tlb->freed_tables;
+	bool last_level = !(tlb->freed_tables || tlb->unshared_tables);
 	unsigned long stride = tlb_get_unmap_size(tlb);
 	int tlb_level = tlb_get_level(tlb);
 

2.53.0