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


From: Andrey Smetanin
Subject: Re: [Qemu-devel] [PATCH v1] kvm/x86: Hyper-V tsc page setup
Date: Tue, 12 Jan 2016 10:43:50 +0300
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101 Thunderbird/38.0.1

ping
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 <address@hidden>
CC: Paolo Bonzini <address@hidden>
CC: Gleb Natapov <address@hidden>
CC: Roman Kagan <address@hidden>
CC: Denis V. Lunev <address@hidden>
CC: address@hidden

---
  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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