4.19-stable review patch. If anyone has any objections, please let me know.
------------------
From: Andi Kleen <ak@xxxxxxxxxxxxxxx>
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@xxxxxxxxxxxxxxx>
Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: stable@xxxxxxxxxxxxxxx
Link: https://lore.kernel.org/all/20240808000244.946864-1-ak@xxxxxxxxxxxxxxx
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
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);
