linux-kernel - [PATCH 24/26] KVM: x86: Clear output regs for CPUID 0x14 if PT isn't exposed to guest

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Date:   Wed, 29 Jan 2020 15:46:38 -0800
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
Subject: [PATCH 24/26] KVM: x86: Clear output regs for CPUID 0x14 if PT isn't exposed to guest

Clear the output regs for the main CPUID 0x14 leaf (index=0) if Intel PT
isn't exposed to the guest.  Leaf 0x14 enumerates Intel PT capabilities
and should return zeroes if PT is not supported.  Incorrectly reporting
PT capabilities is essentially a cosmetic error, i.e. doesn't negatively
affect any known kernel, as the existence of PT itself is correctly
enumerated via CPUID 0x7.

Signed-off-by: Sean Christopherson <sean.j.christopherson@...el.com>
---
 arch/x86/kvm/cpuid.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
index eb61a1d83598..d06fb54c9c0d 100644
--- a/arch/x86/kvm/cpuid.c
+++ b/arch/x86/kvm/cpuid.c
@@ -651,8 +651,10 @@ static inline int __do_cpuid_func(struct kvm_cpuid_entry2 *entry, u32 function,
 	case 0x14: {
 		int t, times = entry->eax;
 
-		if (!f_intel_pt)
+		if (!f_intel_pt) {
+			entry->eax = entry->ebx = entry->ecx = entry->edx = 0;
 			break;
+		}
 
 		for (t = 1; t <= times; ++t) {
 			if (*nent >= maxnent)
-- 
2.24.1