Re: [PATCH v1] kvm/x86: Hyper-V tsc page setup

["Denis V. Lunev" <den@openvz.org>]

On 12/24/2015 12:33 PM, Andrey Smetanin wrote:
> Lately tsc page was implemented but filled with empty
> values. This patch setup tsc page scale and offset based
> on vcpu tsc, tsc_khz and  HV_X64_MSR_TIME_REF_COUNT value.
>
> The valid tsc page drops HV_X64_MSR_TIME_REF_COUNT msr
> reads count to zero which potentially improves performance.
>
> The patch applies on top of
> 'kvm: Make vcpu->requests as 64 bit bitmap'
> previously sent.
>
> Signed-off-by: Andrey Smetanin <asmetanin@virtuozzo.com>
> CC: Paolo Bonzini <pbonzini@redhat.com>
> CC: Gleb Natapov <gleb@kernel.org>
> CC: Roman Kagan <rkagan@virtuozzo.com>
> CC: Denis V. Lunev <den@openvz.org>
> CC: qemu-devel@nongnu.org
>
> ---
>   arch/x86/kvm/hyperv.c    | 117 +++++++++++++++++++++++++++++++++++++++++------
>   arch/x86/kvm/hyperv.h    |   2 +
>   arch/x86/kvm/x86.c       |  12 +++++
>   include/linux/kvm_host.h |   1 +
>   4 files changed, 117 insertions(+), 15 deletions(-)
>
> diff --git a/arch/x86/kvm/hyperv.c b/arch/x86/kvm/hyperv.c
> index d50675a..504fdc7 100644
> --- a/arch/x86/kvm/hyperv.c
> +++ b/arch/x86/kvm/hyperv.c
> @@ -753,6 +753,105 @@ static int kvm_hv_msr_set_crash_data(struct kvm_vcpu *vcpu,
>   	return 0;
>   }
>   
> +static u64 calc_tsc_page_scale(u32 tsc_khz)
> +{
> +	/*
> +	 * reftime (in 100ns) = tsc * tsc_scale / 2^64 + tsc_offset
> +	 * so reftime_delta = (tsc_delta * tsc_scale) / 2^64
> +	 * so tsc_scale = (2^64 * reftime_delta)/tsc_delta
> +	 * so tsc_scale = (2^64 * 10 * 10^6) / tsc_hz = (2^64 * 10000) / tsc_khz
> +	 * so tsc_scale = (2^63 * 2 * 10000) / tsc_khz
> +	 */
> +	return mul_u64_u32_div(1ULL << 63, 2 * 10000, tsc_khz);
> +}
> +
> +static int write_tsc_page(struct kvm *kvm, u64 gfn,
> +			  PHV_REFERENCE_TSC_PAGE tsc_ref)
> +{
> +	if (kvm_write_guest(kvm, gfn_to_gpa(gfn),
> +			    tsc_ref, sizeof(*tsc_ref)))
> +		return 1;
> +	mark_page_dirty(kvm, gfn);
> +	return 0;
> +}
> +
> +static int read_tsc_page(struct kvm *kvm, u64 gfn,
> +			 PHV_REFERENCE_TSC_PAGE tsc_ref)
> +{
> +	if (kvm_read_guest(kvm, gfn_to_gpa(gfn),
> +			   tsc_ref, sizeof(*tsc_ref)))
> +		return 1;
> +	return 0;
> +}
> +
> +static u64 calc_tsc_page_time(struct kvm_vcpu *vcpu,
> +			      PHV_REFERENCE_TSC_PAGE tsc_ref)
> +{
> +
> +	u64 tsc = kvm_read_l1_tsc(vcpu, rdtsc());
> +
> +	return mul_u64_u64_shr(tsc, tsc_ref->tsc_scale, 64)
> +		+ tsc_ref->tsc_offset;
> +}
> +
> +static int setup_blank_tsc_page(struct kvm_vcpu *vcpu, u64 gfn)
> +{
> +	HV_REFERENCE_TSC_PAGE tsc_ref;
> +
> +	memset(&tsc_ref, 0, sizeof(tsc_ref));
> +	return write_tsc_page(vcpu->kvm, gfn, &tsc_ref);
> +}
> +
> +int kvm_hv_setup_tsc_page(struct kvm_vcpu *vcpu)
> +{
> +	struct kvm *kvm = vcpu->kvm;
> +	struct kvm_hv *hv = &kvm->arch.hyperv;
> +	HV_REFERENCE_TSC_PAGE tsc_ref;
> +	u32 tsc_khz;
> +	int r;
> +	u64 gfn, ref_time, tsc_scale, tsc_offset, tsc;
> +
> +	if (WARN_ON_ONCE(!(hv->hv_tsc_page & HV_X64_MSR_TSC_REFERENCE_ENABLE)))
> +		return -EINVAL;
> +
> +	gfn = hv->hv_tsc_page >> HV_X64_MSR_TSC_REFERENCE_ADDRESS_SHIFT;
> +	vcpu_debug(vcpu, "tsc page gfn 0x%llx\n", gfn);
> +
> +	tsc_khz = vcpu->arch.virtual_tsc_khz;
> +	if (!tsc_khz) {
> +		vcpu_unimpl(vcpu, "no tsc khz\n");
> +		return setup_blank_tsc_page(vcpu, gfn);
> +	}
> +
> +	r = read_tsc_page(kvm, gfn, &tsc_ref);
> +	if (r) {
> +		vcpu_err(vcpu, "can't access tsc page gfn 0x%llx\n", gfn);
> +		return r;
> +	}
> +
> +	tsc_scale = calc_tsc_page_scale(tsc_khz);
> +	ref_time = get_time_ref_counter(kvm);
> +	tsc = kvm_read_l1_tsc(vcpu, rdtsc());
> +
> +	/* tsc_offset = reftime - tsc * tsc_scale / 2^64 */
> +	tsc_offset = ref_time - mul_u64_u64_shr(tsc, tsc_scale, 64);
> +	vcpu_debug(vcpu, "tsc khz %u tsc %llu scale %llu offset %llu\n",
> +		   tsc_khz, tsc, tsc_scale, tsc_offset);
> +
> +	tsc_ref.tsc_sequence++;
> +	if (tsc_ref.tsc_sequence == 0)
> +		tsc_ref.tsc_sequence = 1;
> +
> +	tsc_ref.tsc_scale = tsc_scale;
> +	tsc_ref.tsc_offset = tsc_offset;
> +
> +	vcpu_debug(vcpu, "tsc page calibration time %llu vs. reftime %llu\n",
> +		   calc_tsc_page_time(vcpu, &tsc_ref),
> +		   get_time_ref_counter(kvm));
> +
> +	return write_tsc_page(kvm, gfn, &tsc_ref);
> +}
> +
>   static int kvm_hv_set_msr_pw(struct kvm_vcpu *vcpu, u32 msr, u64 data,
>   			     bool host)
>   {
> @@ -790,23 +889,11 @@ static int kvm_hv_set_msr_pw(struct kvm_vcpu *vcpu, u32 msr, u64 data,
>   		mark_page_dirty(kvm, gfn);
>   		break;
>   	}
> -	case HV_X64_MSR_REFERENCE_TSC: {
> -		u64 gfn;
> -		HV_REFERENCE_TSC_PAGE tsc_ref;
> -
> -		memset(&tsc_ref, 0, sizeof(tsc_ref));
> +	case HV_X64_MSR_REFERENCE_TSC:
>   		hv->hv_tsc_page = data;
> -		if (!(data & HV_X64_MSR_TSC_REFERENCE_ENABLE))
> -			break;
> -		gfn = data >> HV_X64_MSR_TSC_REFERENCE_ADDRESS_SHIFT;
> -		if (kvm_write_guest(
> -				kvm,
> -				gfn << HV_X64_MSR_TSC_REFERENCE_ADDRESS_SHIFT,
> -				&tsc_ref, sizeof(tsc_ref)))
> -			return 1;
> -		mark_page_dirty(kvm, gfn);
> +		if (hv->hv_tsc_page & HV_X64_MSR_TSC_REFERENCE_ENABLE)
> +			kvm_make_request(KVM_REQ_HV_TSC_PAGE, vcpu);
>   		break;
> -	}
>   	case HV_X64_MSR_CRASH_P0 ... HV_X64_MSR_CRASH_P4:
>   		return kvm_hv_msr_set_crash_data(vcpu,
>   						 msr - HV_X64_MSR_CRASH_P0,
> diff --git a/arch/x86/kvm/hyperv.h b/arch/x86/kvm/hyperv.h
> index 60eccd4..e7cc446 100644
> --- a/arch/x86/kvm/hyperv.h
> +++ b/arch/x86/kvm/hyperv.h
> @@ -84,4 +84,6 @@ static inline bool kvm_hv_has_stimer_pending(struct kvm_vcpu *vcpu)
>   
>   void kvm_hv_process_stimers(struct kvm_vcpu *vcpu);
>   
> +int kvm_hv_setup_tsc_page(struct kvm_vcpu *vcpu);
> +
>   #endif
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index aedb1a0..1d821f6 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -6500,6 +6500,18 @@ static int vcpu_enter_guest(struct kvm_vcpu *vcpu)
>   		 */
>   		if (kvm_check_request(KVM_REQ_HV_STIMER, vcpu))
>   			kvm_hv_process_stimers(vcpu);
> +
> +		/*
> +		 * KVM_REQ_HV_TSC_PAGE setup should be after
> +		 * KVM_REQ_CLOCK_UPDATE processing because
> +		 * Hyper-V tsc page content depends
> +		 * on kvm->arch.kvmclock_offset value.
> +		 */
> +		if (kvm_check_request(KVM_REQ_HV_TSC_PAGE, vcpu)) {
> +			r = kvm_hv_setup_tsc_page(vcpu);
> +			if (unlikely(r))
> +				goto out;
> +		}
>   	}
>   
>   	/*
> diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
> index 6877b4d7e..93c9e25 100644
> --- a/include/linux/kvm_host.h
> +++ b/include/linux/kvm_host.h
> @@ -145,6 +145,7 @@ static inline bool is_error_page(struct page *page)
>   #define KVM_REQ_HV_RESET          29
>   #define KVM_REQ_HV_EXIT           30
>   #define KVM_REQ_HV_STIMER         31
> +#define KVM_REQ_HV_TSC_PAGE       32
>   
>   #define KVM_REQ_MAX               64
>   
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