linux-kernel - [PATCH v3 01/57] KVM: x86: Use feature_bit() to clear CONSTANT

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Message-ID: <20241128013424.4096668-2-seanjc@google.com>
Date: Wed, 27 Nov 2024 17:33:28 -0800
From: Sean Christopherson <seanjc@...gle.com>
To: Paolo Bonzini <pbonzini@...hat.com>, Sean Christopherson <seanjc@...gle.com>, 
	Vitaly Kuznetsov <vkuznets@...hat.com>, Jarkko Sakkinen <jarkko@...nel.org>
Cc: kvm@...r.kernel.org, linux-sgx@...r.kernel.org, 
	linux-kernel@...r.kernel.org, Maxim Levitsky <mlevitsk@...hat.com>, 
	Hou Wenlong <houwenlong.hwl@...group.com>, Xiaoyao Li <xiaoyao.li@...el.com>, 
	Kechen Lu <kechenl@...dia.com>, Oliver Upton <oliver.upton@...ux.dev>, 
	Binbin Wu <binbin.wu@...ux.intel.com>, Yang Weijiang <weijiang.yang@...el.com>, 
	Robert Hoo <robert.hoo.linux@...il.com>
Subject: [PATCH v3 01/57] KVM: x86: Use feature_bit() to clear CONSTANT_TSC
 when emulating CPUID

When clearing CONSTANT_TSC during CPUID emulation due to a Hyper-V quirk,
use feature_bit() instead of SF() to ensure the bit is actually cleared.
SF() evaluates to zero if the _host_ doesn't support the feature.  I.e.
KVM could keep the bit set if userspace advertised CONSTANT_TSC despite
it not being supported in hardware.

Note, translating from a scattered feature to a the hardware version is
done by __feature_translate(), not SF().  The sole purpose of SF() is to
check kernel support for the scattered feature, *before* translation.

Cc: Vitaly Kuznetsov <vkuznets@...hat.com>
Signed-off-by: Sean Christopherson <seanjc@...gle.com>
---
 arch/x86/kvm/cpuid.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
index 097bdc022d0f..776f24408fa3 100644
--- a/arch/x86/kvm/cpuid.c
+++ b/arch/x86/kvm/cpuid.c
@@ -1630,7 +1630,7 @@ bool kvm_cpuid(struct kvm_vcpu *vcpu, u32 *eax, u32 *ebx,
 				*ebx &= ~(F(RTM) | F(HLE));
 		} else if (function == 0x80000007) {
 			if (kvm_hv_invtsc_suppressed(vcpu))
-				*edx &= ~SF(CONSTANT_TSC);
+				*edx &= ~feature_bit(CONSTANT_TSC);
 		}
 	} else {
 		*eax = *ebx = *ecx = *edx = 0;
-- 
2.47.0.338.g60cca15819-goog