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

Commit-ID: 919f18f961c03d6694aa726c514184f2311a4614 Gitweb: https://git.kernel.org/tip/919f18f961c03d6694aa726c514184f2311a4614 Author: Andi Kleen ak@linux.intel.com AuthorDate: Wed, 07 Aug 2024 17:02:44 -07:00 Committer: Thomas Gleixner tglx@linutronix.de CommitterDate: Thu, 08 Aug 2024 17:03:12 +02:00

x86/mtrr: Check if fixed MTRRs exist before saving them

MTRRs have an obsolete fixed variant for fine grained caching control of the 640K-1MB region that uses separate MSRs. This fixed variant has a separate capability bit in the MTRR capability MSR.

So far all x86 CPUs which support MTRR have this separate bit set, so it went unnoticed that mtrr_save_state() does not check the capability bit before accessing the fixed MTRR MSRs.

Though on a CPU that does not support the fixed MTRR capability this results in a #GP. The #GP itself is harmless because the RDMSR fault is handled gracefully, but results in a WARN_ON().

Add the missing capability check to prevent this.

Fixes: 2b1f6278d77c ("[PATCH] x86: Save the MTRRs of the BSP before booting an AP") Signed-off-by: Andi Kleen ak@linux.intel.com Signed-off-by: Thomas Gleixner tglx@linutronix.de Cc: stable@vger.kernel.org Link: https://lore.kernel.org/all/20240808000244.946864-1-ak@linux.intel.com --- arch/x86/kernel/cpu/mtrr/mtrr.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/x86/kernel/cpu/mtrr/mtrr.c b/arch/x86/kernel/cpu/mtrr/mtrr.c index 767bf1c..2a2fc14 100644 --- a/arch/x86/kernel/cpu/mtrr/mtrr.c +++ b/arch/x86/kernel/cpu/mtrr/mtrr.c @@ -609,7 +609,7 @@ void mtrr_save_state(void) { int first_cpu;

- if (!mtrr_enabled()) + if (!mtrr_enabled() || !mtrr_state.have_fixed) return;

first_cpu = cpumask_first(cpu_online_mask);