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Subject[PATCH v2] mce: use safe MSR accesses
Date
From: Jesse Larrew <jesse.larrew@amd.com>

Certain MSRs are only relevant to a kernel in host mode, and kvm had
chosen not to implement these MSRs at all for guests. If a guest kernel
ever tried to access these MSRs, the result was a general protection
fault.

KVM will be separately patched to return 0 when these MSRs are read,
and this patch ensures that MSR accesses are tolerant of exceptions.

Signed-off-by: Jesse Larrew <jesse.larrew@amd.com>
---
arch/x86/kernel/cpu/mcheck/mce.c | 11 +++--------
1 file changed, 3 insertions(+), 8 deletions(-)

diff --git a/arch/x86/kernel/cpu/mcheck/mce.c b/arch/x86/kernel/cpu/mcheck/mce.c
index 61a9668ce..2737ced 100644
--- a/arch/x86/kernel/cpu/mcheck/mce.c
+++ b/arch/x86/kernel/cpu/mcheck/mce.c
@@ -1540,7 +1540,7 @@ static int __mcheck_cpu_apply_quirks(struct cpuinfo_x86 *c)
if (c->x86 == 0x15 &&
(c->x86_model >= 0x10 && c->x86_model <= 0x1f)) {
int i;
- u64 val, hwcr;
+ u64 hwcr;
bool need_toggle;
u32 msrs[] = {
0x00000413, /* MC4_MISC0 */
@@ -1556,13 +1556,8 @@ static int __mcheck_cpu_apply_quirks(struct cpuinfo_x86 *c)
wrmsrl(MSR_K7_HWCR, hwcr | BIT(18));

for (i = 0; i < ARRAY_SIZE(msrs); i++) {
- rdmsrl(msrs[i], val);
-
- /* CntP bit set? */
- if (val & BIT_64(62)) {
- val &= ~BIT_64(62);
- wrmsrl(msrs[i], val);
- }
+ /* Clear CntP bit safely */
+ msr_clear_bit(msrs[i], 62);
}

/* restore old settings */
--
1.9.1


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