linux-kernel - [PATCH] KVM: x86: Restore update of required xstate size in guest's CPUID

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Date:   Fri,  8 May 2020 16:37:49 -0700
From:   Sean Christopherson <sean.j.christopherson@...el.com>
To:     Paolo Bonzini <pbonzini@...hat.com>
Cc:     Sean Christopherson <sean.j.christopherson@...el.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org, Xiaoyao Li <xiaoyao.li@...el.com>
Subject: [PATCH] KVM: x86: Restore update of required xstate size in guest's CPUID

Restore a guest CPUID update that was unintentional collateral damage
when the per-vCPU guest_xstate_size field was removed.

Cc: Xiaoyao Li <xiaoyao.li@...el.com>
Fixes: d87277414b851 ("kvm: x86: Cleanup vcpu->arch.guest_xstate_size")
Signed-off-by: Sean Christopherson <sean.j.christopherson@...el.com>
---

There's nothing more thrilling than watching bisect home in on your own
commits, only to land on someone else's on the very last step.

 arch/x86/kvm/cpuid.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
index 35845704cf57a..cd708b0b460a0 100644
--- a/arch/x86/kvm/cpuid.c
+++ b/arch/x86/kvm/cpuid.c
@@ -84,11 +84,13 @@ int kvm_update_cpuid(struct kvm_vcpu *vcpu)
 				   kvm_read_cr4_bits(vcpu, X86_CR4_PKE));
 
 	best = kvm_find_cpuid_entry(vcpu, 0xD, 0);
-	if (!best)
+	if (!best) {
 		vcpu->arch.guest_supported_xcr0 = 0;
-	else
+	} else {
 		vcpu->arch.guest_supported_xcr0 =
 			(best->eax | ((u64)best->edx << 32)) & supported_xcr0;
+		best->ebx = xstate_required_size(vcpu->arch.xcr0, false);
+	}
 
 	best = kvm_find_cpuid_entry(vcpu, 0xD, 1);
 	if (best && (cpuid_entry_has(best, X86_FEATURE_XSAVES) ||
-- 
2.26.0