From: David Woodhouse <dwmw2@infradead.org>
To: kvm@vger.kernel.org
Cc: Paolo Bonzini <pbonzini@redhat.com>,
Jonathan Corbet <corbet@lwn.net>,
Sean Christopherson <seanjc@google.com>,
Thomas Gleixner <tglx@linutronix.de>,
Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
Dave Hansen <dave.hansen@linux.intel.com>,
x86@kernel.org, "H. Peter Anvin" <hpa@zytor.com>,
Paul Durrant <paul@xen.org>, Shuah Khan <shuah@kernel.org>,
linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org,
linux-kselftest@vger.kernel.org,
Oliver Upton <oliver.upton@linux.dev>,
Marcelo Tosatti <mtosatti@redhat.com>,
jalliste@amazon.co.uk, sveith@amazon.de, zide.chen@intel.com,
Dongli Zhang <dongli.zhang@oracle.com>
Subject: [PATCH v2 05/15] KVM: x86: Explicitly disable TSC scaling without CONSTANT_TSC
Date: Sat, 27 Apr 2024 12:05:02 +0100 [thread overview]
Message-ID: <20240427111929.9600-6-dwmw2@infradead.org> (raw)
In-Reply-To: <20240427111929.9600-1-dwmw2@infradead.org>
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>
Reviewed-by: Paul Durrant <paul@xen.org>
---
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
next prev parent reply other threads:[~2024-04-27 11:19 UTC|newest]
Thread overview: 22+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-04-27 11:04 [RFC PATCH v2] Cleaning up the KVM clock mess David Woodhouse
2024-04-27 11:04 ` [PATCH v2 01/15] KVM: x86/xen: Do not corrupt KVM clock in kvm_xen_shared_info_init() David Woodhouse
2024-05-04 7:42 ` Marcelo Tosatti
2024-05-07 19:08 ` David Woodhouse
2024-04-27 11:04 ` [PATCH v2 02/15] KVM: x86: Improve accuracy of KVM clock when TSC scaling is in force David Woodhouse
2024-04-27 11:05 ` [PATCH v2 03/15] KVM: x86: Add KVM_[GS]ET_CLOCK_GUEST for accurate KVM clock migration David Woodhouse
2024-04-27 11:05 ` [PATCH v2 04/15] KVM: selftests: Add KVM/PV clock selftest to prove timer correction David Woodhouse
2024-04-27 11:05 ` David Woodhouse [this message]
2024-04-27 11:05 ` [PATCH v2 06/15] KVM: x86: Add KVM_VCPU_TSC_SCALE and fix the documentation on TSC migration David Woodhouse
2024-04-27 11:05 ` [PATCH v2 07/15] KVM: x86: Avoid NTP frequency skew for KVM clock on 32-bit host David Woodhouse
2024-04-27 11:05 ` [PATCH v2 08/15] KVM: x86: Fix KVM clock precision in __get_kvmclock() David Woodhouse
2024-04-27 11:05 ` [PATCH v2 09/15] KVM: x86: Fix software TSC upscaling in kvm_update_guest_time() David Woodhouse
2024-04-27 11:05 ` [PATCH v2 10/15] KVM: x86: Simplify and comment kvm_get_time_scale() David Woodhouse
2024-04-27 11:05 ` [PATCH v2 11/15] KVM: x86: Remove implicit rdtsc() from kvm_compute_l1_tsc_offset() David Woodhouse
2024-04-27 11:05 ` [PATCH v2 12/15] KVM: x86: Improve synchronization in kvm_synchronize_tsc() David Woodhouse
2024-04-27 11:05 ` [PATCH v2 13/15] KVM: x86: Kill cur_tsc_{nsec,offset,write} fields David Woodhouse
2024-05-10 9:03 ` Chenyi Qiang
2024-05-14 13:17 ` David Woodhouse
2024-04-27 11:05 ` [PATCH v2 14/15] KVM: x86: Allow KVM master clock mode when TSCs are offset from each other David Woodhouse
2024-04-27 11:05 ` [PATCH v2 15/15] KVM: x86: Factor out kvm_use_master_clock() David Woodhouse
2024-05-01 17:55 ` Chen, Zide
2024-05-01 20:45 ` David Woodhouse
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