From 8953e599b13320239ced8e2422f95a1286847d93 Mon Sep 17 00:00:00 2001
Message-Id: <8953e599b13320239ced8e2422f95a1286847d93@dist-git>
From: Jiri Denemark <jdenemar@redhat.com>
Date: Tue, 4 Jun 2019 13:04:29 +0200
Subject: [PATCH] util: Add virHostCPUGetTscInfo
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On a KVM x86_64 host which supports invariant TSC this function can be
used to detect the TSC frequency and the availability of TSC scaling.

The magic MSR numbers required to check if VMX scaling is supported on
the host are documented in Volume 3 of the Intel® 64 and IA-32
Architectures Software Developer’s Manual.

Signed-off-by: Jiri Denemark <jdenemar@redhat.com>
(cherry picked from commit f0f6faba63becfab38c928905ac6ed79f9a318b8)

https://bugzilla.redhat.com/show_bug.cgi?id=1641702

Conflicts:
	src/util/virhostcpu.h
            - virenum.h doesn't exist downstream, the content is still
              in virutil.h
            - the comment after #endif changed upstream

Signed-off-by: Jiri Denemark <jdenemar@redhat.com>
Message-Id: <b44a5f67b95fde34eacabf86c47c1c278d4cf03f.1559646067.git.jdenemar@redhat.com>
Reviewed-by: Ján Tomko <jtomko@redhat.com>
---
 src/util/virhostcpu.c | 71 +++++++++++++++++++++++++++++++++++++++++++
 src/util/virhostcpu.h | 11 +++++++
 2 files changed, 82 insertions(+)

diff --git a/src/util/virhostcpu.c b/src/util/virhostcpu.c
index 1b6570568c..0f84780e09 100644
--- a/src/util/virhostcpu.c
+++ b/src/util/virhostcpu.c
@@ -1364,6 +1364,69 @@ virHostCPUGetMSR(unsigned long index,
     return virHostCPUGetMSRFromKVM(index, msr);
 }
 
+
+# define VMX_PROCBASED_CTLS2_MSR 0x48b
+# define VMX_USE_TSC_SCALING (1 << 25)
+
+/*
+ * This function should only be called when the host CPU supports invariant TSC
+ * (invtsc CPUID feature).
+ *
+ * Returns pointer to the TSC info structure on success,
+ *         NULL when TSC cannot be probed otherwise.
+ */
+virHostCPUTscInfoPtr
+virHostCPUGetTscInfo(void)
+{
+    virHostCPUTscInfoPtr info;
+    VIR_AUTOCLOSE kvmFd = -1;
+    VIR_AUTOCLOSE vmFd = -1;
+    VIR_AUTOCLOSE vcpuFd = -1;
+    uint64_t msr = 0;
+    int rc;
+
+    if ((kvmFd = open(KVM_DEVICE, O_RDONLY)) < 0) {
+        virReportSystemError(errno, _("Unable to open %s"), KVM_DEVICE);
+        return NULL;
+    }
+
+    if ((vmFd = ioctl(kvmFd, KVM_CREATE_VM, 0)) < 0) {
+        virReportSystemError(errno, "%s",
+                             _("Unable to create KVM VM for TSC probing"));
+        return NULL;
+    }
+
+    if ((vcpuFd = ioctl(vmFd, KVM_CREATE_VCPU, 0)) < 0) {
+        virReportSystemError(errno, "%s",
+                             _("Unable to create KVM vCPU for TSC probing"));
+        return NULL;
+    }
+
+    if ((rc = ioctl(vcpuFd, KVM_GET_TSC_KHZ)) < 0) {
+        virReportSystemError(errno, "%s",
+                             _("Unable to probe TSC frequency"));
+        return NULL;
+    }
+
+    if (VIR_ALLOC(info) < 0)
+        return NULL;
+
+    info->frequency = rc * 1000ULL;
+
+    if (virHostCPUGetMSR(VMX_PROCBASED_CTLS2_MSR, &msr) == 0) {
+        /* High 32 bits of the MSR value indicate whether specific control
+         * can be set to 1. */
+        msr >>= 32;
+
+        info->scaling = virTristateBoolFromBool(!!(msr & VMX_USE_TSC_SCALING));
+    }
+
+    VIR_DEBUG("Detected TSC frequency %llu Hz, scaling %s",
+              info->frequency, virTristateBoolTypeToString(info->scaling));
+
+    return info;
+}
+
 #else
 
 int
@@ -1375,6 +1438,14 @@ virHostCPUGetMSR(unsigned long index ATTRIBUTE_UNUSED,
     return -1;
 }
 
+virHostCPUTscInfoPtr
+virHostCPUGetTscInfo(void)
+{
+    virReportSystemError(ENOSYS, "%s",
+                         _("Probing TSC is not supported on this platform"));
+    return NULL;
+}
+
 #endif /* HAVE_LINUX_KVM_H && defined(KVM_GET_MSRS) && \
           (defined(__i386__) || defined(__x86_64__)) && \
           (defined(__linux__) || defined(__FreeBSD__)) */
diff --git a/src/util/virhostcpu.h b/src/util/virhostcpu.h
index e705623d4f..ee9d755c83 100644
--- a/src/util/virhostcpu.h
+++ b/src/util/virhostcpu.h
@@ -27,6 +27,15 @@
 # include "internal.h"
 # include "virarch.h"
 # include "virbitmap.h"
+# include "virutil.h"
+
+
+typedef struct _virHostCPUTscInfo virHostCPUTscInfo;
+typedef virHostCPUTscInfo *virHostCPUTscInfoPtr;
+struct _virHostCPUTscInfo {
+    unsigned long long frequency;
+    virTristateBool scaling;
+};
 
 
 int virHostCPUGetStats(int cpuNum,
@@ -71,4 +80,6 @@ unsigned int virHostCPUGetMicrocodeVersion(void);
 int virHostCPUGetMSR(unsigned long index,
                      uint64_t *msr);
 
+virHostCPUTscInfoPtr virHostCPUGetTscInfo(void);
+
 #endif /* __VIR_HOSTCPU_H__*/
-- 
2.21.0