linux-kernel - [tip: x86/mtrr] x86/mtrr: Check if fixed-range MTRRs exist in mtrr_save_fixed

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Message-ID: <174706026285.406.13641034613218376274.tip-bot2@tip-bot2>
Date: Mon, 12 May 2025 14:31:02 -0000
From: "tip-bot2 for Jiaqing Zhao" <tip-bot2@...utronix.de>
To: linux-tip-commits@...r.kernel.org
Cc: Jiaqing Zhao <jiaqing.zhao@...ux.intel.com>,
 "Borislav Petkov (AMD)" <bp@...en8.de>, x86@...nel.org,
 linux-kernel@...r.kernel.org
Subject: [tip: x86/mtrr] x86/mtrr: Check if fixed-range MTRRs exist in
 mtrr_save_fixed_ranges()

The following commit has been merged into the x86/mtrr branch of tip:

Commit-ID:     824c6384e8d9275d4ec7204f3f79a4ac6bc10379
Gitweb:        https://git.kernel.org/tip/824c6384e8d9275d4ec7204f3f79a4ac6bc10379
Author:        Jiaqing Zhao <jiaqing.zhao@...ux.intel.com>
AuthorDate:    Fri, 09 May 2025 17:06:33 
Committer:     Borislav Petkov (AMD) <bp@...en8.de>
CommitterDate: Mon, 12 May 2025 13:04:40 +02:00

x86/mtrr: Check if fixed-range MTRRs exist in mtrr_save_fixed_ranges()

When suspending, save_processor_state() calls mtrr_save_fixed_ranges()
to save fixed-range MTRRs.

On platforms without fixed-range MTRRs like the ACRN hypervisor which
has removed fixed-range MTRR emulation, accessing these MSRs will
trigger an unchecked MSR access error. Make sure fixed-range MTRRs are
supported before access to prevent such error.

Since mtrr_state.have_fixed is only set when MTRRs are present and
enabled, checking the CPU feature flag in mtrr_save_fixed_ranges() is
unnecessary.

Fixes: 3ebad5905609 ("[PATCH] x86: Save and restore the fixed-range MTRRs of the BSP when suspending")
Signed-off-by: Jiaqing Zhao <jiaqing.zhao@...ux.intel.com>
Signed-off-by: Borislav Petkov (AMD) <bp@...en8.de>
Link: https://lore.kernel.org/20250509170633.3411169-2-jiaqing.zhao@linux.intel.com
---
 arch/x86/kernel/cpu/mtrr/generic.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/x86/kernel/cpu/mtrr/generic.c b/arch/x86/kernel/cpu/mtrr/generic.c
index e2c6b47..8c18327 100644
--- a/arch/x86/kernel/cpu/mtrr/generic.c
+++ b/arch/x86/kernel/cpu/mtrr/generic.c
@@ -593,7 +593,7 @@ static void get_fixed_ranges(mtrr_type *frs)
 
 void mtrr_save_fixed_ranges(void *info)
 {
-	if (boot_cpu_has(X86_FEATURE_MTRR))
+	if (mtrr_state.have_fixed)
 		get_fixed_ranges(mtrr_state.fixed_ranges);
 }