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Commit 72c139ba authored by Ladi Prosek's avatar Ladi Prosek Committed by Paolo Bonzini
Browse files

KVM: hyperv: support HV_X64_MSR_TSC_FREQUENCY and HV_X64_MSR_APIC_FREQUENCY 



It has been experimentally confirmed that supporting these two MSRs is one
of the necessary conditions for nested Hyper-V to use the TSC page. Modern
Windows guests are noticeably slower when they fall back to reading
timestamps from the HV_X64_MSR_TIME_REF_COUNT MSR instead of using the TSC
page.

The newly supported MSRs are advertised with the AccessFrequencyRegs
partition privilege flag and CPUID.40000003H:EDX[8] "Support for
determining timer frequencies is available" (both outside of the scope of
this KVM patch).

Reviewed-by: default avatarRadim Krčmář <rkrcmar@redhat.com>
Signed-off-by: default avatarLadi Prosek <lprosek@redhat.com>
Signed-off-by: default avatarPaolo Bonzini <pbonzini@redhat.com>
parent aae4e7a8

arch/x86/kvm/hyperv.c

+6 −0
Original line number Diff line number Diff line
@@ -1160,6 +1160,12 @@ static int kvm_hv_get_msr(struct kvm_vcpu *vcpu, u32 msr, u64 *pdata) 
		return stimer_get_count(vcpu_to_stimer(vcpu, timer_index),

					pdata);

	}

	case HV_X64_MSR_TSC_FREQUENCY:

		data = (u64)vcpu->arch.virtual_tsc_khz * 1000;

		break;

	case HV_X64_MSR_APIC_FREQUENCY:

		data = APIC_BUS_FREQUENCY;

		break;

	default:

		vcpu_unimpl(vcpu, "Hyper-V unhandled rdmsr: 0x%x\n", msr);

		return 1;

arch/x86/kvm/lapic.c

+0 −2
Original line number Diff line number Diff line
@@ -54,8 +54,6 @@ 
#define PRIu64 "u"

#define PRIo64 "o"



#define APIC_BUS_CYCLE_NS 1



/* #define apic_debug(fmt,arg...) printk(KERN_WARNING fmt,##arg) */

#define apic_debug(fmt, arg...)

arch/x86/kvm/lapic.h

+3 −0
Original line number Diff line number Diff line
@@ -12,6 +12,9 @@ 
#define KVM_APIC_SHORT_MASK	0xc0000

#define KVM_APIC_DEST_MASK	0x800



#define APIC_BUS_CYCLE_NS       1

#define APIC_BUS_FREQUENCY      (1000000000ULL / APIC_BUS_CYCLE_NS)



struct kvm_timer {

	struct hrtimer timer;

	s64 period; 				/* unit: ns */

arch/x86/kvm/x86.c

+1 −0
Original line number Diff line number Diff line
@@ -993,6 +993,7 @@ static u32 emulated_msrs[] = { 
	MSR_KVM_SYSTEM_TIME_NEW, MSR_KVM_WALL_CLOCK_NEW,

	HV_X64_MSR_GUEST_OS_ID, HV_X64_MSR_HYPERCALL,

	HV_X64_MSR_TIME_REF_COUNT, HV_X64_MSR_REFERENCE_TSC,

	HV_X64_MSR_TSC_FREQUENCY, HV_X64_MSR_APIC_FREQUENCY,

	HV_X64_MSR_CRASH_P0, HV_X64_MSR_CRASH_P1, HV_X64_MSR_CRASH_P2,

	HV_X64_MSR_CRASH_P3, HV_X64_MSR_CRASH_P4, HV_X64_MSR_CRASH_CTL,

	HV_X64_MSR_RESET,