[PATCH v10 4/8] KVM: X86: Refresh CPUID on guest XSS change

[Yang Weijiang]

CPUID(0xd, 1) reports the current required storage size of
XCR0 | XSS, when guest updates the XSS, it's necessary to update
the CPUID leaf, otherwise guest will fetch stale state, this
result into some WARNs during guest running.

Co-developed-by: Zhang Yi Z <yi.z.zhang@xxxxxxxxxxxxxxx>
Signed-off-by: Zhang Yi Z <yi.z.zhang@xxxxxxxxxxxxxxx>
Signed-off-by: Yang Weijiang <weijiang.yang@xxxxxxxxx>
---
 arch/x86/kvm/cpuid.c | 18 +++++++++++++++---
 arch/x86/kvm/x86.c   |  7 ++++++-
 2 files changed, 21 insertions(+), 4 deletions(-)

diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
index 78d461be2102..71703d9277ee 100644
--- a/arch/x86/kvm/cpuid.c
+++ b/arch/x86/kvm/cpuid.c
@@ -95,9 +95,21 @@ int kvm_update_cpuid(struct kvm_vcpu *vcpu)
 	}
 
 	best = kvm_find_cpuid_entry(vcpu, 0xD, 1);
-	if (best && (cpuid_entry_has(best, X86_FEATURE_XSAVES) ||
-		     cpuid_entry_has(best, X86_FEATURE_XSAVEC)))
-		best->ebx = xstate_required_size(vcpu->arch.xcr0, true);
+	if (best) {
+		if (best->eax & (F(XSAVES) | F(XSAVEC))) {
+			u64 xstate = vcpu->arch.xcr0 | vcpu->arch.ia32_xss;
+
+			best->ebx = xstate_required_size(xstate, true);
+		}
+
+		if (best->eax & F(XSAVES)) {
+			supported_xss &= best->ecx | ((u64)best->edx << 32);
+		} else {
+			best->ecx = 0;
+			best->edx = 0;
+			supported_xss = 0;
+		}
+	}
 
 	/*
 	 * The existing code assumes virtual address is 48-bit or 57-bit in the
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 90acdbbb8a5a..5be6fad6e08d 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -2838,7 +2838,10 @@ int kvm_set_msr_common(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
 		 */
 		if (data & ~supported_xss)
 			return 1;
-		vcpu->arch.ia32_xss = data;
+		if (vcpu->arch.ia32_xss != data) {
+			vcpu->arch.ia32_xss = data;
+			kvm_update_cpuid(vcpu);
+		}
 		break;
 	case MSR_SMI_COUNT:
 		if (!msr_info->host_initiated)
@@ -9635,6 +9638,8 @@ int kvm_arch_hardware_setup(void)
 
 	if (!kvm_cpu_cap_has(X86_FEATURE_XSAVES))
 		supported_xss = 0;
+	else
+		supported_xss = host_xss & KVM_SUPPORTED_XSS;
 
 	cr4_reserved_bits = kvm_host_cr4_reserved_bits(&boot_cpu_data);
 
-- 
2.17.2