From 6094ea6111dd57274b6037e76f662a06b8e5c9d1 Mon Sep 17 00:00:00 2001

Message-Id: <6094ea6111dd57274b6037e76f662a06b8e5c9d1@dist-git>

From: Jiri Denemark <jdenemar@redhat.com>

Date: Fri, 21 Jun 2019 09:25:43 +0200

Subject: [PATCH] vircpuhost: Add support for reading MSRs

MIME-Version: 1.0

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The new virHostCPUGetMSR internal API will try to read the MSR from

/dev/cpu/0/msr and if it is not possible (the device does not exist or

libvirt is running unprivileged), it will fallback to asking KVM for the

MSR using KVM_GET_MSRS ioctl.

Signed-off-by: Jiri Denemark <jdenemar@redhat.com>

Reviewed-by: Ján Tomko <jtomko@redhat.com>

(cherry picked from commit df4b46737f43a1a67f9b5de2840213a1bd2b3cce)

https://bugzilla.redhat.com/show_bug.cgi?id=1697627

Conflicts:

	src/util/virhostcpu.h

            - different header file guard symbol

Signed-off-by: Jiri Denemark <jdenemar@redhat.com>

Message-Id: <0d4c18704c435cccc2b18ebd55f4f914caf05d13.1561068591.git.jdenemar@redhat.com>

Reviewed-by: Ján Tomko <jtomko@redhat.com>

---

 src/libvirt_private.syms |  1 +

 src/util/virhostcpu.c    | 80 ++++++++++++++++++++++++++++++++++++++++

 src/util/virhostcpu.h    |  3 ++

 3 files changed, 84 insertions(+)

diff --git a/src/libvirt_private.syms b/src/libvirt_private.syms

index 347667b17c..9ebc5384fb 100644

--- a/src/libvirt_private.syms

+++ b/src/libvirt_private.syms

@@ -1974,6 +1974,7 @@ virHostCPUGetInfo;

 virHostCPUGetKVMMaxVCPUs;

 virHostCPUGetMap;

 virHostCPUGetMicrocodeVersion;

+virHostCPUGetMSR;

 virHostCPUGetOnline;

 virHostCPUGetOnlineBitmap;

 virHostCPUGetPresentBitmap;

diff --git a/src/util/virhostcpu.c b/src/util/virhostcpu.c

index effe04ca3a..d0c47faa18 100644

--- a/src/util/virhostcpu.c

+++ b/src/util/virhostcpu.c

@@ -64,6 +64,7 @@

 VIR_LOG_INIT("util.hostcpu");

 #define KVM_DEVICE "/dev/kvm"

+#define MSR_DEVICE "/dev/cpu/0/msr"

 #if defined(__FreeBSD__) || defined(__APPLE__)

@@ -1266,3 +1267,82 @@ virHostCPUGetMicrocodeVersion(void)

 }

 #endif /* __linux__ */

+

+

+#if HAVE_LINUX_KVM_H && defined(KVM_GET_MSRS)

+static int

+virHostCPUGetMSRFromKVM(unsigned long index,

+                        uint64_t *result)

+{

+    VIR_AUTOCLOSE fd = -1;

+    struct {

+        struct kvm_msrs header;

+        struct kvm_msr_entry entry;

+    } msr = {

+        .header = { .nmsrs = 1 },

+        .entry = { .index = index },

+    };

+

+    if ((fd = open(KVM_DEVICE, O_RDONLY)) < 0) {

+        virReportSystemError(errno, _("Unable to open %s"), KVM_DEVICE);

+        return -1;

+    }

+

+    if (ioctl(fd, KVM_GET_MSRS, &msr) < 0) {

+        VIR_DEBUG("Cannot get MSR 0x%lx from KVM", index);

+        return 1;

+    }

+

+    *result = msr.entry.data;

+    return 0;

+}

+

+#else

+

+static int

+virHostCPUGetMSRFromKVM(unsigned long index ATTRIBUTE_UNUSED,

+                        uint64_t *result ATTRIBUTE_UNUSED)

+{

+    virReportSystemError(ENOSYS, "%s",

+                         _("Reading MSRs via KVM is not supported on this platform"));

+    return -1;

+}

+#endif /* HAVE_LINUX_KVM_H && defined(KVM_GET_MSRS) */

+

+

+/*

+ * Returns 0 on success,

+ *         1 when the MSR is not supported by the host CPU,

+*         -1 on error.

+ */

+int

+virHostCPUGetMSR(unsigned long index,

+                 uint64_t *msr)

+{

+    VIR_AUTOCLOSE fd = -1;

+    char ebuf[1024];

+

+    *msr = 0;

+

+    if ((fd = open(MSR_DEVICE, O_RDONLY)) < 0) {

+        VIR_DEBUG("Unable to open %s: %s",

+                  MSR_DEVICE, virStrerror(errno, ebuf, sizeof(ebuf)));

+    } else {

+        int rc = pread(fd, msr, sizeof(*msr), index);

+

+        if (rc == sizeof(*msr))

+            return 0;

+

+        if (rc < 0 && errno == EIO) {

+            VIR_DEBUG("CPU does not support MSR 0x%lx", index);

+            return 1;

+        }

+

+        VIR_DEBUG("Cannot read MSR 0x%lx from %s: %s",

+                  index, MSR_DEVICE, virStrerror(errno, ebuf, sizeof(ebuf)));

+    }

+

+    VIR_DEBUG("Falling back to KVM ioctl");

+

+    return virHostCPUGetMSRFromKVM(index, msr);

+}

diff --git a/src/util/virhostcpu.h b/src/util/virhostcpu.h

index f9f3359288..e705623d4f 100644

--- a/src/util/virhostcpu.h

+++ b/src/util/virhostcpu.h

@@ -68,4 +68,7 @@ int virHostCPUGetOnline(unsigned int cpu, bool *online);

 unsigned int virHostCPUGetMicrocodeVersion(void);

+int virHostCPUGetMSR(unsigned long index,

+                     uint64_t *msr);

+

 #endif /* __VIR_HOSTCPU_H__*/

-- 

2.22.0