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    SubjectRe: [PATCH 03/17] Unify vendor TSC logic
    Zachary Amsden wrote:
    > Move the TSC control logic from the vendor backends into x86.c
    > by adding adjust_tsc_offset to x86 ops. Now all TSC decisions
    > can be done in one place.
    >
    > Also, rename some variable in the VCPU structure to more accurately
    > reflect their actual content.
    >
    > VMX backend would record last observed TSC very late (possibly in an
    > IPI to clear the VMCS from a remote CPU), now it is done earlier.
    >
    > Note this is still not yet perfect. We adjust TSC in both
    > directions when the TSC is unstable, resulting in desynchronized
    > TSCs for SMP guests. A better choice would be to compensate based
    > on a master reference clock.
    >
    > Signed-off-by: Zachary Amsden <zamsden@redhat.com>
    > ---
    > arch/x86/include/asm/kvm_host.h | 5 +++--
    > arch/x86/kvm/svm.c | 25 +++++++++++--------------
    > arch/x86/kvm/vmx.c | 20 ++++++++------------
    > arch/x86/kvm/x86.c | 16 +++++++++++-----
    > 4 files changed, 33 insertions(+), 33 deletions(-)
    >
    > diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
    > index 91631b8..94f6ce8 100644
    > --- a/arch/x86/include/asm/kvm_host.h
    > +++ b/arch/x86/include/asm/kvm_host.h
    > @@ -253,7 +253,6 @@ struct kvm_mmu {
    > };
    >
    > struct kvm_vcpu_arch {
    > - u64 host_tsc;
    > /*
    > * rip and regs accesses must go through
    > * kvm_{register,rip}_{read,write} functions.
    > @@ -334,9 +333,10 @@ struct kvm_vcpu_arch {
    >
    > gpa_t time;
    > struct pvclock_vcpu_time_info hv_clock;
    > - unsigned int hv_clock_tsc_khz;
    > + unsigned int hw_tsc_khz;
    > unsigned int time_offset;
    > struct page *time_page;
    > + u64 last_host_tsc;
    >
    > bool nmi_pending;
    > bool nmi_injected;
    > @@ -530,6 +530,7 @@ struct kvm_x86_ops {
    > u64 (*get_mt_mask)(struct kvm_vcpu *vcpu, gfn_t gfn, bool is_mmio);
    > int (*get_lpage_level)(void);
    > bool (*rdtscp_supported)(void);
    > + void (*adjust_tsc_offset)(struct kvm_vcpu *vcpu, s64 adjustment);
    >
    > void (*set_supported_cpuid)(u32 func, struct kvm_cpuid_entry2 *entry);
    >
    > diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c
    > index 09b2145..ee2cf30 100644
    > --- a/arch/x86/kvm/svm.c
    > +++ b/arch/x86/kvm/svm.c
    > @@ -948,18 +948,6 @@ static void svm_vcpu_load(struct kvm_vcpu *vcpu, int cpu)
    > int i;
    >
    > if (unlikely(cpu != vcpu->cpu)) {
    > - u64 delta;
    > -
    > - if (check_tsc_unstable()) {
    > - /*
    > - * Make sure that the guest sees a monotonically
    > - * increasing TSC.
    > - */
    > - delta = vcpu->arch.host_tsc - native_read_tsc();
    > - svm->vmcb->control.tsc_offset += delta;
    > - if (is_nested(svm))
    > - svm->nested.hsave->control.tsc_offset += delta;
    > - }
    > svm->asid_generation = 0;
    > }
    >
    > @@ -975,8 +963,6 @@ static void svm_vcpu_put(struct kvm_vcpu *vcpu)
    > ++vcpu->stat.host_state_reload;
    > for (i = 0; i < NR_HOST_SAVE_USER_MSRS; i++)
    > wrmsrl(host_save_user_msrs[i], svm->host_user_msrs[i]);
    > -
    > - vcpu->arch.host_tsc = native_read_tsc();
    > }
    >
    > static unsigned long svm_get_rflags(struct kvm_vcpu *vcpu)
    > @@ -3422,6 +3408,15 @@ static bool svm_rdtscp_supported(void)
    > return false;
    > }
    >
    > +static void svm_adjust_tsc_offset(struct kvm_vcpu *vcpu, s64 adjustment)
    > +{
    > + struct vcpu_svm *svm = to_svm(vcpu);
    > +
    > + svm->vmcb->control.tsc_offset += adjustment;
    > + if (is_nested(svm))
    > + svm->nested.hsave->control.tsc_offset += adjustment;
    > +}
    > +
    > static void svm_fpu_deactivate(struct kvm_vcpu *vcpu)
    > {
    > struct vcpu_svm *svm = to_svm(vcpu);
    > @@ -3506,6 +3501,8 @@ static struct kvm_x86_ops svm_x86_ops = {
    > .rdtscp_supported = svm_rdtscp_supported,
    >
    > .set_supported_cpuid = svm_set_supported_cpuid,
    > +
    > + .adjust_tsc_offset = svm_adjust_tsc_offset,
    > };
    >
    > static int __init svm_init(void)
    > diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
    > index a657e08..a993e67 100644
    > --- a/arch/x86/kvm/vmx.c
    > +++ b/arch/x86/kvm/vmx.c
    > @@ -498,7 +498,6 @@ static void __vcpu_clear(void *arg)
    > vmcs_clear(vmx->vmcs);
    > if (per_cpu(current_vmcs, cpu) == vmx->vmcs)
    > per_cpu(current_vmcs, cpu) = NULL;
    > - rdtscll(vmx->vcpu.arch.host_tsc);
    > list_del(&vmx->local_vcpus_link);
    > vmx->vcpu.cpu = -1;
    > vmx->launched = 0;
    > @@ -881,7 +880,6 @@ static void vmx_load_host_state(struct vcpu_vmx *vmx)
    > static void vmx_vcpu_load(struct kvm_vcpu *vcpu, int cpu)
    > {
    > struct vcpu_vmx *vmx = to_vmx(vcpu);
    > - u64 tsc_this, delta, new_offset;
    > u64 phys_addr = __pa(per_cpu(vmxarea, cpu));
    >
    > if (!vmm_exclusive)
    > @@ -914,16 +912,6 @@ static void vmx_vcpu_load(struct kvm_vcpu *vcpu, int cpu)
    >
    > rdmsrl(MSR_IA32_SYSENTER_ESP, sysenter_esp);
    > vmcs_writel(HOST_IA32_SYSENTER_ESP, sysenter_esp); /* 22.2.3 */
    > -
    > - /*
    > - * Make sure the time stamp counter is monotonous.
    > - */
    > - rdtscll(tsc_this);
    > - if (tsc_this < vcpu->arch.host_tsc) {
    > - delta = vcpu->arch.host_tsc - tsc_this;
    > - new_offset = vmcs_read64(TSC_OFFSET) + delta;
    > - vmcs_write64(TSC_OFFSET, new_offset);
    > - }
    > }
    > }
    >
    > @@ -1153,6 +1141,12 @@ static void guest_write_tsc(u64 guest_tsc, u64 host_tsc)
    > vmcs_write64(TSC_OFFSET, guest_tsc - host_tsc);
    > }
    >
    > +static void vmx_adjust_tsc_offset(struct kvm_vcpu *vcpu, s64 adjustment)
    > +{
    > + u64 offset = vmcs_read64(TSC_OFFSET);
    > + vmcs_write64(TSC_OFFSET, offset + adjustment);
    > +}
    > +
    > /*
    > * Reads an msr value (of 'msr_index') into 'pdata'.
    > * Returns 0 on success, non-0 otherwise.
    > @@ -4340,6 +4334,8 @@ static struct kvm_x86_ops vmx_x86_ops = {
    > .rdtscp_supported = vmx_rdtscp_supported,
    >
    > .set_supported_cpuid = vmx_set_supported_cpuid,
    > +
    > + .adjust_tsc_offset = vmx_adjust_tsc_offset,
    > };
    >
    > static int __init vmx_init(void)
    > diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
    > index 0a102d3..c8289d0 100644
    > --- a/arch/x86/kvm/x86.c
    > +++ b/arch/x86/kvm/x86.c
    > @@ -929,9 +929,9 @@ static int kvm_write_guest_time(struct kvm_vcpu *v)
    > return 1;
    > }
    >
    > - if (unlikely(vcpu->hv_clock_tsc_khz != this_tsc_khz)) {
    > + if (unlikely(vcpu->hw_tsc_khz != this_tsc_khz)) {
    > kvm_set_time_scale(this_tsc_khz, &vcpu->hv_clock);
    > - vcpu->hv_clock_tsc_khz = this_tsc_khz;
    > + vcpu->hw_tsc_khz = this_tsc_khz;
    > }
    >
    > /* Keep irq disabled to prevent changes to the clock */
    > @@ -1805,18 +1805,24 @@ out:
    >
    > void kvm_arch_vcpu_load(struct kvm_vcpu *vcpu, int cpu)
    > {
    > + kvm_x86_ops->vcpu_load(vcpu, cpu);
    > if (unlikely(vcpu->cpu != cpu)) {
    > + /* Make sure TSC doesn't go backwards */
    > + s64 tsc_delta = !vcpu->arch.last_host_tsc ? 0 :
    > + native_read_tsc() - vcpu->arch.last_host_tsc;
    > + if (tsc_delta < 0 || check_tsc_unstable())
    >
    It's better to do the adjustment also when tsc_delta > 0
    > + kvm_x86_ops->adjust_tsc_offset(vcpu, -tsc_delta);
    > kvm_migrate_timers(vcpu);
    > + kvm_request_guest_time_update(vcpu);
    > + vcpu->cpu = cpu;
    > }
    > - kvm_x86_ops->vcpu_load(vcpu, cpu);
    > - kvm_request_guest_time_update(vcpu);
    > - vcpu->cpu = cpu;
    > }
    >
    > void kvm_arch_vcpu_put(struct kvm_vcpu *vcpu)
    > {
    > kvm_x86_ops->vcpu_put(vcpu);
    > kvm_put_guest_fpu(vcpu);
    > + vcpu->arch.last_host_tsc = native_read_tsc();
    > }
    >
    > static int is_efer_nx(void)
    >



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