linux-kernel - [PATCH 5.10 256/289] KVM: x86: Emulate RDPID only if RDTSCP is supported

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Message-Id: <20210517140313.762996034@linuxfoundation.org>
Date:   Mon, 17 May 2021 16:03:01 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Sean Christopherson <seanjc@...gle.com>,
        Jim Mattson <jmattson@...gle.com>,
        Reiji Watanabe <reijiw@...gle.com>,
        Paolo Bonzini <pbonzini@...hat.com>
Subject: [PATCH 5.10 256/289] KVM: x86: Emulate RDPID only if RDTSCP is supported

From: Sean Christopherson <seanjc@...gle.com>

commit 85d0011264da24be08ae907d7f29983a597ca9b1 upstream.

Do not advertise emulation support for RDPID if RDTSCP is unsupported.
RDPID emulation subtly relies on MSR_TSC_AUX to exist in hardware, as
both vmx_get_msr() and svm_get_msr() will return an error if the MSR is
unsupported, i.e. ctxt->ops->get_msr() will fail and the emulator will
inject a #UD.

Note, RDPID emulation also relies on RDTSCP being enabled in the guest,
but this is a KVM bug and will eventually be fixed.

Fixes: fb6d4d340e05 ("KVM: x86: emulate RDPID")
Cc: stable@...r.kernel.org
Signed-off-by: Sean Christopherson <seanjc@...gle.com>
Message-Id: <20210504171734.1434054-3-seanjc@...gle.com>
Reviewed-by: Jim Mattson <jmattson@...gle.com>
Reviewed-by: Reiji Watanabe <reijiw@...gle.com>
Signed-off-by: Paolo Bonzini <pbonzini@...hat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 arch/x86/kvm/cpuid.c |    3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

--- a/arch/x86/kvm/cpuid.c
+++ b/arch/x86/kvm/cpuid.c
@@ -572,7 +572,8 @@ static int __do_cpuid_func_emulated(stru
 	case 7:
 		entry->flags |= KVM_CPUID_FLAG_SIGNIFCANT_INDEX;
 		entry->eax = 0;
-		entry->ecx = F(RDPID);
+		if (kvm_cpu_cap_has(X86_FEATURE_RDTSCP))
+			entry->ecx = F(RDPID);
 		++array->nent;
 	default:
 		break;