From 5df2c49263338da7221f24b3ad67ffd21d88047c Mon Sep 17 00:00:00 2001 From: =?UTF-8?q?Daniel=20P=2E=20Berrang=C3=A9?= Date: Wed, 4 Aug 2021 18:05:59 +0100 Subject: [PATCH] util: directly query KVM for TSC scaling support MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit We currently query the host MSRs to determine if TSC scaling is supported. This works OK when running privileged and can open the /dev/cpu/0/msr. When unprivileged we fallback to querying MSRs from /dev/kvm. This is incorrect because /dev/kvm only reports accurate info for MSRs that are valid to use from inside a guest. The TSC scaling support MSR is not, thus we always end up reporting lack of TSC scaling when unprivileged. The solution to this is easy, because KVM can directly report whether TSC scaling is available, which matches what QEMU will do at startup. Closes: https://gitlab.com/libvirt/libvirt/-/issues/188 Reported-by: Roman Mohr Reviewed-by: Michal Privoznik Signed-off-by: Daniel P. Berrangé --- src/util/virhostcpu.c | 22 +++++++--------------- 1 file changed, 7 insertions(+), 15 deletions(-) diff --git a/src/util/virhostcpu.c b/src/util/virhostcpu.c index 7aa92ad11d..5dd2baf2df 100644 --- a/src/util/virhostcpu.c +++ b/src/util/virhostcpu.c @@ -1336,9 +1336,6 @@ virHostCPUGetMSR(unsigned long index, } -# 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). @@ -1349,11 +1346,10 @@ virHostCPUGetMSR(unsigned long index, virHostCPUTscInfo * virHostCPUGetTscInfo(void) { - virHostCPUTscInfo *info; + g_autofree virHostCPUTscInfo *info = g_new0(virHostCPUTscInfo, 1); 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) { @@ -1378,23 +1374,19 @@ virHostCPUGetTscInfo(void) _("Unable to probe TSC frequency")); return NULL; } - - info = g_new0(virHostCPUTscInfo, 1); - 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)); + if ((rc = ioctl(kvmFd, KVM_CHECK_EXTENSION, KVM_CAP_TSC_CONTROL)) < 0) { + virReportSystemError(errno, "%s", + _("Unable to query TSC scaling support")); + return NULL; } + info->scaling = rc ? VIR_TRISTATE_BOOL_YES : VIR_TRISTATE_BOOL_NO; VIR_DEBUG("Detected TSC frequency %llu Hz, scaling %s", info->frequency, virTristateBoolTypeToString(info->scaling)); - return info; + return g_steal_pointer(&info); } #else