[PATCH 3/3] KVM: x86: Flush guest TLB on MTRR MSR writes

[Jim Mattson <jmattson@google.com>]

Per both the AMD APM and the Intel SDM, writing to an MTRR with WRMSR is an
implicit TLB invalidation that invalidates all TLB entries (including
global entries). [The APM uses the word, "update," which could be construed
to mean "modify," but it is unclear.]

Previously, kvm_mtrr_set_msr() stored the updated MTRR state without
requesting a TLB flush. This broke x86 architectural compliance by leaving
existing TLB entries in hardware. Additionally, on AMD CPUs supporting
ERAPS, omitting the TLB flush request meant VCPU_REG_ERAPS was never
dirtied on MTRR writes, leaving the Return Address Predictor (RAP/RSB)
uncleared.

Issue a KVM_REQ_TLB_FLUSH_GUEST request on every MTRR MSR write to match
x86 architectural semantics.

Fixes: 9ba075a664df ("KVM: MTRR support")
Assisted-by: Gemini:Gemini-Next
Signed-off-by: Jim Mattson <jmattson@google.com>
---
 arch/x86/kvm/mtrr.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/arch/x86/kvm/mtrr.c b/arch/x86/kvm/mtrr.c
index 6f74e2b27c1e..ca5e5c7f7022 100644
--- a/arch/x86/kvm/mtrr.c
+++ b/arch/x86/kvm/mtrr.c
@@ -105,6 +105,7 @@ int kvm_mtrr_set_msr(struct kvm_vcpu *vcpu, u32 msr, u64 data)
 		return 1;
 
 	*mtrr = data;
+	kvm_make_request(KVM_REQ_TLB_FLUSH_GUEST, vcpu);
 	return 0;
 }
 
-- 
2.55.0.229.g6434b31f56-goog