lkml.org 
[lkml]   [2024]   [Apr]   [18]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
Patch in this message
/
From
Subject[PATCH 05/10] KVM: x86: Explicitly disable TSC scaling without CONSTANT_TSC
Date
From: David Woodhouse <dwmw@amazon.co.uk>

KVM does make an attempt to cope with non-constant TSC, and has notifiers
to handle host TSC frequency changes. However, it *only* adjusts the KVM
clock, and doesn't adjust TSC frequency scaling when the host changes.

This is presumably because non-constant TSCs were fixed in hardware long
before TSC scaling was implemented, so there should never be real CPUs
which have TSC scaling but *not* CONSTANT_TSC.

Such a combination could potentially happen in some odd L1 nesting
environment, but it isn't worth trying to support it. Just make the
dependency explicit.

Signed-off-by: David Woodhouse <dwmw@amazon.co.uk>
---
arch/x86/kvm/svm/svm.c | 3 ++-
arch/x86/kvm/vmx/vmx.c | 2 +-
2 files changed, 3 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
index 0f3b59da0d4a..4d3ec1c3231e 100644
--- a/arch/x86/kvm/svm/svm.c
+++ b/arch/x86/kvm/svm/svm.c
@@ -5202,7 +5202,8 @@ static __init int svm_hardware_setup(void)
kvm_enable_efer_bits(EFER_FFXSR);

if (tsc_scaling) {
- if (!boot_cpu_has(X86_FEATURE_TSCRATEMSR)) {
+ if (!boot_cpu_has(X86_FEATURE_TSCRATEMSR) ||
+ !boot_cpu_has(X86_FEATURE_CONSTANT_TSC)) {
tsc_scaling = false;
} else {
pr_info("TSC scaling supported\n");
diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index 6780313914f8..bee830adf744 100644
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -8428,7 +8428,7 @@ __init int vmx_hardware_setup(void)
if (!enable_apicv || !cpu_has_vmx_ipiv())
enable_ipiv = false;

- if (cpu_has_vmx_tsc_scaling())
+ if (cpu_has_vmx_tsc_scaling() && boot_cpu_has(X86_FEATURE_CONSTANT_TSC))
kvm_caps.has_tsc_control = true;

kvm_caps.max_tsc_scaling_ratio = KVM_VMX_TSC_MULTIPLIER_MAX;
--
2.44.0

\
 
 \ /
  Last update: 2024-04-18 21:43    [W:0.147 / U:0.616 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site