linux-kernel - [PATCH 2/3] x86/mm: Fix early boot use of INVPLGB

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Message-ID: <20250602133402.3385163-3-riel@surriel.com>
Date: Mon,  2 Jun 2025 09:30:56 -0400
From: Rik van Riel <riel@...riel.com>
To: linux-kernel@...r.kernel.org
Cc: kernel-team@...a.com,
	dave.hansen@...ux.intel.com,
	luto@...nel.org,
	peterz@...radead.org,
	bp@...en8.de,
	x86@...nel.org,
	yu-cheng.yu@...el.com,
	Rik van Riel <riel@...riel.com>,
	stable@...nel.org
Subject: [PATCH 2/3] x86/mm: Fix early boot use of INVPLGB

Use of the INVLPGB instruction is done based off the X86_FEATURE_INVLPGB
CPU feature, which is provided directly by the hardware.

If invlpgb_kernel_range_flush is called before the kernel has read
the value of invlpgb_count_max from the hardware, the normally
bounded loop can become an infinite loop if invlpgb_count_max is
initialized to zero.

Fix that issue by initializing invlpgb_count_max to 1.

This way INVPLGB at early boot time will be a little bit slower
than normal (with initialized invplgb_count_max), and not an
instant hang at bootup time.

Signed-off-by: Rik van Riel <riel@...riel.com>
Fixes: b7aa05cbdc52 ("x86/mm: Add INVLPGB support code")
Cc: stable@...nel.org
---
 arch/x86/kernel/cpu/amd.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/x86/kernel/cpu/amd.c b/arch/x86/kernel/cpu/amd.c
index 93da466dfe2c..b2ad8d13211a 100644
--- a/arch/x86/kernel/cpu/amd.c
+++ b/arch/x86/kernel/cpu/amd.c
@@ -31,7 +31,7 @@

 #include "cpu.h"

-u16 invlpgb_count_max __ro_after_init;
+u16 invlpgb_count_max __ro_after_init = 1;

 static inline int rdmsrq_amd_safe(unsigned msr, u64 *p)
 {
-- 
2.49.0