[PATCH 2/3] KVM: x86: Virtualize HWCR.TscFreqSel[bit 24]

[Jim Mattson <jmattson@google.com>]

On certain CPUs, Linux guests expect HWCR.TscFreqSel[bit 24] to be
set. If it isn't set, they complain:
	[Firmware Bug]: TSC doesn't count with P0 frequency!

Eliminate this complaint by setting the bit on virtual processors for
which Linux guests expect it to be set.

Note that this bit is read-only on said processors.

Signed-off-by: Jim Mattson <jmattson@google.com>
---
 arch/x86/kvm/cpuid.c | 10 ++++++++++
 arch/x86/kvm/x86.c   |  7 +++++++
 2 files changed, 17 insertions(+)

diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
index 0544e30b4946..2d7dcd13dcc3 100644
--- a/arch/x86/kvm/cpuid.c
+++ b/arch/x86/kvm/cpuid.c
@@ -373,6 +373,16 @@ static void kvm_vcpu_after_set_cpuid(struct kvm_vcpu *vcpu)
 	vcpu->arch.maxphyaddr = cpuid_query_maxphyaddr(vcpu);
 	vcpu->arch.reserved_gpa_bits = kvm_vcpu_reserved_gpa_bits_raw(vcpu);
 
+	/*
+	 * HWCR.TscFreqSel[bit 24] has a reset value of 1 on some processors.
+	 */
+	if (guest_cpuid_is_amd_or_hygon(vcpu) &&
+	    guest_cpuid_has(vcpu, X86_FEATURE_CONSTANT_TSC) &&
+	    (guest_cpuid_family(vcpu) > 0x10 ||
+	     (guest_cpuid_family(vcpu) == 0x10 &&
+	      guest_cpuid_model(vcpu) >= 2)))
+		vcpu->arch.msr_hwcr |= BIT(24);
+
 	kvm_pmu_refresh(vcpu);
 	vcpu->arch.cr4_guest_rsvd_bits =
 	    __cr4_reserved_bits(guest_cpuid_has, vcpu);
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 3421ed7fcee0..cb02a7c2938b 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -3699,12 +3699,19 @@ int kvm_set_msr_common(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
 		data &= ~(u64)0x40;	/* ignore flush filter disable */
 		data &= ~(u64)0x100;	/* ignore ignne emulation enable */
 		data &= ~(u64)0x8;	/* ignore TLB cache disable */
+		data &= ~(u64)0x1000000;/* ignore TscFreqSel */
 
 		/* Handle McStatusWrEn */
 		if (data & ~BIT_ULL(18)) {
 			kvm_pr_unimpl_wrmsr(vcpu, msr, data);
 			return 1;
 		}
+
+		/*
+		 * When set, TscFreqSel is read-only. Attempts to
+		 * clear it are ignored.
+		 */
+		data |= vcpu->arch.msr_hwcr & BIT_ULL(24);
 		vcpu->arch.msr_hwcr = data;
 		break;
 	case MSR_FAM10H_MMIO_CONF_BASE:
-- 
2.42.0.515.g380fc7ccd1-goog