linux-kernel - [PATCH] x86/mm: Fix flush_tlb_range() when used for zapping normal PMDs

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Message-Id: <20250103-x86-collapse-flush-fix-v1-1-3c521856cfa6@google.com>
Date: Fri, 03 Jan 2025 19:39:38 +0100
From: Jann Horn <jannh@...gle.com>
To: Dave Hansen <dave.hansen@...ux.intel.com>, 
 Andy Lutomirski <luto@...nel.org>, Peter Zijlstra <peterz@...radead.org>
Cc: Rik van Riel <riel@...riel.com>, linux-kernel@...r.kernel.org, 
 stable@...r.kernel.org, Jann Horn <jannh@...gle.com>
Subject: [PATCH] x86/mm: Fix flush_tlb_range() when used for zapping normal
 PMDs

On the following path, flush_tlb_range() can be used for zapping normal
PMD entries (PMD entries that point to page tables) together with the PTE
entries in the pointed-to page table:

    collapse_pte_mapped_thp
      pmdp_collapse_flush
        flush_tlb_range

The arm64 version of flush_tlb_range() has a comment describing that it can
be used for page table removal, and does not use any last-level
invalidation optimizations. Fix the X86 version by making it behave the
same way.

Currently, X86 only uses this information for the following two purposes,
which I think means the issue doesn't have much impact:

 - In native_flush_tlb_multi() for checking if lazy TLB CPUs need to be
   IPI'd to avoid issues with speculative page table walks.
 - In Hyper-V TLB paravirtualization, again for lazy TLB stuff.

The patch "x86/mm: only invalidate final translations with INVLPGB" which
is currently under review (see
<https://lore.kernel.org/all/20241230175550.4046587-13-riel@surriel.com/>)
would probably be making the impact of this a lot worse.

Cc: stable@...r.kernel.org
Fixes: 016c4d92cd16 ("x86/mm/tlb: Add freed_tables argument to flush_tlb_mm_range")
Signed-off-by: Jann Horn <jannh@...gle.com>
---
 arch/x86/include/asm/tlbflush.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/x86/include/asm/tlbflush.h b/arch/x86/include/asm/tlbflush.h
index 02fc2aa06e9e0ecdba3fe948cafe5892b72e86c0..3da645139748538daac70166618d8ad95116eb74 100644
--- a/arch/x86/include/asm/tlbflush.h
+++ b/arch/x86/include/asm/tlbflush.h
@@ -242,7 +242,7 @@ void flush_tlb_multi(const struct cpumask *cpumask,
 	flush_tlb_mm_range((vma)->vm_mm, start, end,			\
 			   ((vma)->vm_flags & VM_HUGETLB)		\
 				? huge_page_shift(hstate_vma(vma))	\
-				: PAGE_SHIFT, false)
+				: PAGE_SHIFT, true)
 
 extern void flush_tlb_all(void);
 extern void flush_tlb_mm_range(struct mm_struct *mm, unsigned long start,

---
base-commit: aa135d1d0902c49ed45bec98c61c1b4022652b7e
change-id: 20250103-x86-collapse-flush-fix-fa87ac4d5834

-- 
Jann Horn <jannh@...gle.com>