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Date: Wed, 16 Jun 2010 16:10:10 +0800
From: Jason Wang <jasowang@...hat.com>
To: Zachary Amsden <zamsden@...hat.com>
CC: avi@...hat.com, mtosatti@...hat.com, glommer@...hat.com,
kvm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [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@...hat.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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