linux-kernel - [PATCH 1/6] KVM: x86: Fix tracing of CPUID.function when function is out-of-range

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Date:   Mon,  2 Mar 2020 11:57:31 -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, Jan Kiszka <jan.kiszka@...mens.com>,
        Xiaoyao Li <xiaoyao.li@...el.com>
Subject: [PATCH 1/6] KVM: x86: Fix tracing of CPUID.function when function is out-of-range

Rework kvm_cpuid() to query entry->function when adjusting the output
values so that the original function (in the aptly named "function") is
preserved for tracing.  This fixes a bug where trace_kvm_cpuid() will
trace the max function for a range instead of the requested function if
the requested function is out-of-range and an entry for the max function
exists.

Fixes: 43561123ab37 ("kvm: x86: Improve emulation of CPUID leaves 0BH and 1FH")
Reported-by: Jan Kiszka <jan.kiszka@...mens.com>
Cc: Jim Mattson <jmattson@...gle.com>
Cc: Xiaoyao Li <xiaoyao.li@...el.com>
Signed-off-by: Sean Christopherson <sean.j.christopherson@...el.com>
---
 arch/x86/kvm/cpuid.c | 15 +++++++--------
 1 file changed, 7 insertions(+), 8 deletions(-)

diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
index b1c469446b07..6be012937eba 100644
--- a/arch/x86/kvm/cpuid.c
+++ b/arch/x86/kvm/cpuid.c
@@ -997,12 +997,12 @@ static bool cpuid_function_in_range(struct kvm_vcpu *vcpu, u32 function)
 	return max && function <= max->eax;
 }
 
+/* Returns true if the requested leaf/function exists in guest CPUID. */
 bool kvm_cpuid(struct kvm_vcpu *vcpu, u32 *eax, u32 *ebx,
 	       u32 *ecx, u32 *edx, bool check_limit)
 {
-	u32 function = *eax, index = *ecx;
+	const u32 function = *eax, index = *ecx;
 	struct kvm_cpuid_entry2 *entry;
-	struct kvm_cpuid_entry2 *max;
 	bool found;
 
 	entry = kvm_find_cpuid_entry(vcpu, function, index);
@@ -1015,18 +1015,17 @@ bool kvm_cpuid(struct kvm_vcpu *vcpu, u32 *eax, u32 *ebx,
 	 */
 	if (!entry && check_limit && !guest_cpuid_is_amd(vcpu) &&
 	    !cpuid_function_in_range(vcpu, function)) {
-		max = kvm_find_cpuid_entry(vcpu, 0, 0);
-		if (max) {
-			function = max->eax;
-			entry = kvm_find_cpuid_entry(vcpu, function, index);
-		}
+		entry = kvm_find_cpuid_entry(vcpu, 0, 0);
+		if (entry)
+			entry = kvm_find_cpuid_entry(vcpu, entry->eax, index);
 	}
 	if (entry) {
 		*eax = entry->eax;
 		*ebx = entry->ebx;
 		*ecx = entry->ecx;
 		*edx = entry->edx;
-		if (function == 7 && index == 0) {
+
+		if (entry->function == 7 && index == 0) {
 			u64 data;
 		        if (!__kvm_get_msr(vcpu, MSR_IA32_TSX_CTRL, &data, true) &&
 			    (data & TSX_CTRL_CPUID_CLEAR))
-- 
2.24.1