[Xen-devel] [PATCH v4 3/3] x86/viridian: Add partition time reference counter MSR support

[Paul Durrant <paul.durrant@xxxxxxxxxx>]

This patch optionally re-instates support for the partition time reference
counter that was previously introduced by commit
e36cd2cdc9674a7a4855d21fb7b3e6e17c4bb33b and reverted by commit
1cd4fab14ce25859efa4a2af13475e6650a5506c. The previous implementation was
non-optional and flawed.

This implementation uses the tsc of vcpu0, which is preserved across
save/restore as part of the architectural state, and then converts that
to a 100ns tick using the domain's tsc_khz.

Signed-off-by: Paul Durrant <paul.durrant@xxxxxxxxxx>
Cc: Keir Fraser <keir@xxxxxxx>
Cc: Jan Beulich <jbeulich@xxxxxxxx>
Cc: Ian Campbell <ian.campbell@xxxxxxxxxx>
Cc: Ian Jackson <ian.jackson@xxxxxxxxxxxxx>
Cc: Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>
---
 docs/man/xl.cfg.pod.5            |    7 +++++++
 tools/libxl/libxl_dom.c          |    2 ++
 xen/arch/x86/hvm/viridian.c      |   24 +++++++++++++++++++-----
 xen/include/asm-x86/perfc_defn.h |    1 +
 xen/include/public/hvm/params.h  |    9 ++++++++-
 5 files changed, 37 insertions(+), 6 deletions(-)

diff --git a/docs/man/xl.cfg.pod.5 b/docs/man/xl.cfg.pod.5
index a05e831..e4692982 100644
--- a/docs/man/xl.cfg.pod.5
+++ b/docs/man/xl.cfg.pod.5
@@ -1109,6 +1109,13 @@ This set incorporates the TSC and APIC frequency MSRs.
 This enlightenment can improve performance of Windows 7 and Windows
 Server 2008 R2 onwards.
 
+=item B<time-ref-count>
+
+This set incorporates Partition Time Reference Counter MSR.
+
+This enlightenment can improve performance of Windows 8 and Windows
+Server 2012 onwards.
+
 =back
  
 See the latest version of Microsoft's Hypervisor Top-Level Functional
diff --git a/tools/libxl/libxl_dom.c b/tools/libxl/libxl_dom.c
index cc57931..224a4d9 100644
--- a/tools/libxl/libxl_dom.c
+++ b/tools/libxl/libxl_dom.c
@@ -222,6 +222,8 @@ static void hvm_set_viridian_features(libxl__gc *gc, 
uint32_t domid,
             feature_mask |= HVMPV_base_freq;
         else if (strcmp(*p, "freq") == 0)
             feature_mask &= ~HVMPV_no_freq;
+        else if (strcmp(*p, "time-ref-count") == 0)
+            feature_mask |= HVMPV_time_ref_count;
         p++;
     }
 
diff --git a/xen/arch/x86/hvm/viridian.c b/xen/arch/x86/hvm/viridian.c
index 9000375..b92e46f 100644
--- a/xen/arch/x86/hvm/viridian.c
+++ b/xen/arch/x86/hvm/viridian.c
@@ -36,11 +36,11 @@
 #define HvNotifyLongSpinWait    8
 
 /* Viridian CPUID 4000003, Viridian MSR availability. */
-#define CPUID3A_MSR_REF_COUNT   (1 << 1)
-#define CPUID3A_MSR_APIC_ACCESS (1 << 4)
-#define CPUID3A_MSR_HYPERCALL   (1 << 5)
-#define CPUID3A_MSR_VP_INDEX    (1 << 6)
-#define CPUID3A_MSR_FREQ        (1 << 11)
+#define CPUID3A_MSR_TIME_REF_COUNT (1 << 1)
+#define CPUID3A_MSR_APIC_ACCESS    (1 << 4)
+#define CPUID3A_MSR_HYPERCALL      (1 << 5)
+#define CPUID3A_MSR_VP_INDEX       (1 << 6)
+#define CPUID3A_MSR_FREQ           (1 << 11)
 
 /* Viridian CPUID 4000004, Implementation Recommendations. */
 #define CPUID4A_MSR_BASED_APIC  (1 << 3)
@@ -93,6 +93,8 @@ int cpuid_viridian_leaves(unsigned int leaf, unsigned int 
*eax,
                 CPUID3A_MSR_VP_INDEX);
         if ( !(viridian_feature_mask(d) & HVMPV_no_freq) )
             *eax |= CPUID3A_MSR_FREQ;
+        if ( viridian_feature_mask(d) & HVMPV_time_ref_count )
+            *eax |= CPUID3A_MSR_TIME_REF_COUNT;
         break;
     case 4:
         /* Recommended hypercall usage. */
@@ -351,6 +353,18 @@ int rdmsr_viridian_regs(uint32_t idx, uint64_t *val)
         *val = v->arch.hvm_vcpu.viridian.apic_assist.raw;
         break;
 
+    case VIRIDIAN_MSR_TIME_REF_COUNT:
+    {
+        uint64_t tsc;
+
+        if ( !(viridian_feature_mask(d) & HVMPV_time_ref_count) )
+            return 0;
+
+        perfc_incr(mshv_rdmsr_time_ref_count);
+        tsc = hvm_get_guest_tsc(pt_global_vcpu_target(d));
+        *val = (tsc * 10000ull) / d->arch.tsc_khz;
+        break;
+    }
     default:
         return 0;
     }
diff --git a/xen/include/asm-x86/perfc_defn.h b/xen/include/asm-x86/perfc_defn.h
index 7d802cc..170da00 100644
--- a/xen/include/asm-x86/perfc_defn.h
+++ b/xen/include/asm-x86/perfc_defn.h
@@ -120,6 +120,7 @@ PERFCOUNTER(mshv_rdmsr_hc_page,         "MS Hv rdmsr 
hypercall page")
 PERFCOUNTER(mshv_rdmsr_vp_index,        "MS Hv rdmsr vp index")
 PERFCOUNTER(mshv_rdmsr_tsc_frequency,   "MS Hv rdmsr TSC frequency")
 PERFCOUNTER(mshv_rdmsr_apic_frequency,  "MS Hv rdmsr APIC frequency")
+PERFCOUNTER(mshv_rdmsr_time_ref_count,  "MS Hv rdmsr time ref count")
 PERFCOUNTER(mshv_rdmsr_icr,             "MS Hv rdmsr icr")
 PERFCOUNTER(mshv_rdmsr_tpr,             "MS Hv rdmsr tpr")
 PERFCOUNTER(mshv_rdmsr_apic_assist,     "MS Hv rdmsr APIC assist")
diff --git a/xen/include/public/hvm/params.h b/xen/include/public/hvm/params.h
index 68d26fd..3c51072 100644
--- a/xen/include/public/hvm/params.h
+++ b/xen/include/public/hvm/params.h
@@ -88,7 +88,14 @@
 #define _HVMPV_no_freq 1
 #define HVMPV_no_freq  (1 << _HVMPV_no_freq)
 
-#define HVMPV_feature_mask (HVMPV_base_freq|HVMPV_no_freq)
+/* Enable Partition Time Reference Counter (HV_X64_MSR_TIME_REF_COUNT) */
+#define _HVMPV_time_ref_count 2
+#define HVMPV_time_ref_count  (1 << _HVMPV_time_ref_count)
+
+#define HVMPV_feature_mask \
+       (HVMPV_base_freq | \
+        HVMPV_no_freq | \
+        HVMPV_time_ref_count)
 
 #endif
 
-- 
1.7.10.4


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