linux-kernel - [PATCH] Revert "x86: kmsan: sync metadata pages on page fault"

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Date:   Wed, 11 Jan 2023 11:18:06 +0100
From:   Alexander Potapenko <glider@...gle.com>
To:     glider@...gle.com
Cc:     linux-kernel@...r.kernel.org, akpm@...ux-foundation.org,
        peterz@...radead.org, mingo@...hat.com, elver@...gle.com,
        dvyukov@...gle.com, linux-mm@...ck.org, kasan-dev@...glegroups.com,
        luto@...nel.org, tglx@...utronix.de, x86@...nel.org,
        Qun-Wei Lin <qun-wei.lin@...iatek.com>
Subject: [PATCH] Revert "x86: kmsan: sync metadata pages on page fault"

This reverts commit 3f1e2c7a9099c1ed32c67f12cdf432ba782cf51f.

As noticed by Qun-Wei Lin, arch_sync_kernel_mappings() in
arch/x86/mm/fault.c is only used with CONFIG_X86_32, whereas KMSAN is
only supported on x86_64, where this code is not compiled.

The patch in question dates back to downstream KMSAN branch based on
v5.8-rc5, it sneaked into upstream unnoticed in v6.1.

Reported-by: Qun-Wei Lin <qun-wei.lin@...iatek.com>
Link: https://github.com/google/kmsan/issues/91
Signed-off-by: Alexander Potapenko <glider@...gle.com>
---
 arch/x86/mm/fault.c | 23 +----------------------
 1 file changed, 1 insertion(+), 22 deletions(-)

diff --git a/arch/x86/mm/fault.c b/arch/x86/mm/fault.c
index 7b0d4ab894c8b..a498ae1fbe665 100644
--- a/arch/x86/mm/fault.c
+++ b/arch/x86/mm/fault.c
@@ -260,7 +260,7 @@ static noinline int vmalloc_fault(unsigned long address)
 }
 NOKPROBE_SYMBOL(vmalloc_fault);
 
-static void __arch_sync_kernel_mappings(unsigned long start, unsigned long end)
+void arch_sync_kernel_mappings(unsigned long start, unsigned long end)
 {
 	unsigned long addr;
 
@@ -284,27 +284,6 @@ static void __arch_sync_kernel_mappings(unsigned long start, unsigned long end)
 	}
 }
 
-void arch_sync_kernel_mappings(unsigned long start, unsigned long end)
-{
-	__arch_sync_kernel_mappings(start, end);
-#ifdef CONFIG_KMSAN
-	/*
-	 * KMSAN maintains two additional metadata page mappings for the
-	 * [VMALLOC_START, VMALLOC_END) range. These mappings start at
-	 * KMSAN_VMALLOC_SHADOW_START and KMSAN_VMALLOC_ORIGIN_START and
-	 * have to be synced together with the vmalloc memory mapping.
-	 */
-	if (start >= VMALLOC_START && end < VMALLOC_END) {
-		__arch_sync_kernel_mappings(
-			start - VMALLOC_START + KMSAN_VMALLOC_SHADOW_START,
-			end - VMALLOC_START + KMSAN_VMALLOC_SHADOW_START);
-		__arch_sync_kernel_mappings(
-			start - VMALLOC_START + KMSAN_VMALLOC_ORIGIN_START,
-			end - VMALLOC_START + KMSAN_VMALLOC_ORIGIN_START);
-	}
-#endif
-}
-
 static bool low_pfn(unsigned long pfn)
 {
 	return pfn < max_low_pfn;
-- 
2.39.0.314.g84b9a713c41-goog