4.19-stable review patch. If anyone has any objections, please let me know.
------------------
From: Andi Kleen ak@linux.intel.com
commit 919f18f961c03d6694aa726c514184f2311a4614 upstream.
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 Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- arch/x86/kernel/cpu/mtrr/mtrr.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
--- a/arch/x86/kernel/cpu/mtrr/mtrr.c +++ b/arch/x86/kernel/cpu/mtrr/mtrr.c @@ -819,7 +819,7 @@ 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);