linux-kernel - [PATCH] kvm: x86: rewrite kvm_spec_ctrl_valid

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Message-Id: <20200702174455.282252-1-mlevitsk@redhat.com>
Date:   Thu,  2 Jul 2020 20:44:55 +0300
From:   Maxim Levitsky <mlevitsk@...hat.com>
To:     kvm@...r.kernel.org
Cc:     x86@...nel.org (maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)),
        linux-kernel@...r.kernel.org, Joerg Roedel <joro@...tes.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Wanpeng Li <wanpengli@...cent.com>,
        "H. Peter Anvin" <hpa@...or.com>, Borislav Petkov <bp@...en8.de>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Ingo Molnar <mingo@...hat.com>,
        Jim Mattson <jmattson@...gle.com>,
        Sean Christopherson <sean.j.christopherson@...el.com>,
        Maxim Levitsky <mlevitsk@...hat.com>
Subject: [PATCH] kvm: x86: rewrite kvm_spec_ctrl_valid_bits

There are few cases when this function was creating a bogus #GP condition,
for example case when and AMD host supports STIBP but doesn't support SSBD.

Follow the rules for AMD and Intel strictly instead.

AMD #GP rules for IA32_SPEC_CTRL can be found here:
https://bugzilla.kernel.org/show_bug.cgi?id=199889

Fixes: 6441fa6178f5 ("KVM: x86: avoid incorrect writes to host MSR_IA32_SPEC_CTRL")

Signed-off-by: Maxim Levitsky <mlevitsk@...hat.com>
---
 arch/x86/kvm/x86.c | 57 ++++++++++++++++++++++++++++++++++------------
 1 file changed, 42 insertions(+), 15 deletions(-)

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 00c88c2f34e4..a6bed4670b7f 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -10670,27 +10670,54 @@ bool kvm_arch_no_poll(struct kvm_vcpu *vcpu)
 }
 EXPORT_SYMBOL_GPL(kvm_arch_no_poll);
 
-u64 kvm_spec_ctrl_valid_bits(struct kvm_vcpu *vcpu)
+
+static u64 kvm_spec_ctrl_valid_bits_host(void)
+{
+	uint64_t bits = 0;
+
+	if (boot_cpu_has(X86_FEATURE_SPEC_CTRL))
+		bits |= SPEC_CTRL_IBRS;
+	if (boot_cpu_has(X86_FEATURE_INTEL_STIBP))
+		bits |= SPEC_CTRL_STIBP;
+	if (boot_cpu_has(X86_FEATURE_SPEC_CTRL_SSBD))
+		bits |= SPEC_CTRL_SSBD;
+
+	if (boot_cpu_has(X86_FEATURE_AMD_IBRS) || boot_cpu_has(X86_FEATURE_AMD_STIBP))
+		bits |= SPEC_CTRL_STIBP | SPEC_CTRL_IBRS;
+
+	if (boot_cpu_has(X86_FEATURE_AMD_SSBD))
+		bits |= SPEC_CTRL_STIBP | SPEC_CTRL_IBRS | SPEC_CTRL_SSBD;
+
+	return bits;
+}
+
+static u64 kvm_spec_ctrl_valid_bits_guest(struct kvm_vcpu *vcpu)
 {
-	uint64_t bits = SPEC_CTRL_IBRS | SPEC_CTRL_STIBP | SPEC_CTRL_SSBD;
+	uint64_t bits = 0;
 
-	/* The STIBP bit doesn't fault even if it's not advertised */
-	if (!guest_cpuid_has(vcpu, X86_FEATURE_SPEC_CTRL) &&
-	    !guest_cpuid_has(vcpu, X86_FEATURE_AMD_IBRS))
-		bits &= ~(SPEC_CTRL_IBRS | SPEC_CTRL_STIBP);
-	if (!boot_cpu_has(X86_FEATURE_SPEC_CTRL) &&
-	    !boot_cpu_has(X86_FEATURE_AMD_IBRS))
-		bits &= ~(SPEC_CTRL_IBRS | SPEC_CTRL_STIBP);
+	if (guest_cpuid_has(vcpu, X86_FEATURE_SPEC_CTRL))
+		bits |= SPEC_CTRL_IBRS;
+	if (guest_cpuid_has(vcpu, X86_FEATURE_INTEL_STIBP))
+		bits |= SPEC_CTRL_STIBP;
+	if (guest_cpuid_has(vcpu, X86_FEATURE_SPEC_CTRL_SSBD))
+		bits |= SPEC_CTRL_SSBD;
 
-	if (!guest_cpuid_has(vcpu, X86_FEATURE_SPEC_CTRL_SSBD) &&
-	    !guest_cpuid_has(vcpu, X86_FEATURE_AMD_SSBD))
-		bits &= ~SPEC_CTRL_SSBD;
-	if (!boot_cpu_has(X86_FEATURE_SPEC_CTRL_SSBD) &&
-	    !boot_cpu_has(X86_FEATURE_AMD_SSBD))
-		bits &= ~SPEC_CTRL_SSBD;
+	if (guest_cpuid_has(vcpu, X86_FEATURE_AMD_IBRS) ||
+			guest_cpuid_has(vcpu, X86_FEATURE_AMD_STIBP))
+		bits |= SPEC_CTRL_STIBP | SPEC_CTRL_IBRS;
+	if (guest_cpuid_has(vcpu, X86_FEATURE_AMD_SSBD))
+		bits |= SPEC_CTRL_STIBP | SPEC_CTRL_IBRS | SPEC_CTRL_SSBD;
 
 	return bits;
 }
+
+u64 kvm_spec_ctrl_valid_bits(struct kvm_vcpu *vcpu)
+{
+	return kvm_spec_ctrl_valid_bits_host() &
+	       kvm_spec_ctrl_valid_bits_guest(vcpu);
+}
+
+
 EXPORT_SYMBOL_GPL(kvm_spec_ctrl_valid_bits);
 
 EXPORT_TRACEPOINT_SYMBOL_GPL(kvm_exit);
-- 
2.25.4