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backport patch to fix TSC scaling for SVM

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The following issue reported on the community forum [0] is likely
fixed by this.

In my case, loading a VM snapshot that originally was taken on an
Intel CPU on my AMD-based host often caused problems in other VMs. In
particular, it often led to CPU stalls, and sometimes clock jumps far
into the future. With this backport applied, everything seems to run
smoothly even after loading the "bad" snapshot 10 times.

The backport from upstream commit 11d39e8cc43e ("KVM: SVM: fix tsc
scaling cache logic consisted of dropping the parts for nested TSC
scaling, which is not yet present in our kernel, renaming the constant
for the default ratio, and some context changes.

[0] https://forum.proxmox.com/threads/112756/

Signed-off-by: Fiona Ebner <f.ebner@proxmox.com>
This commit is contained in:
Fiona Ebner 2022-09-02 14:44:09 +02:00 committed by Thomas Lamprecht
parent 401e4a8b30
commit 198fde3a16
1 changed files with 113 additions and 0 deletions
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113
patches/kernel/0032-KVM-SVM-fix-tsc-scaling-cache-logic.patch Normal file
View File

@ -0,0 +1,113 @@
From 955c2b4d64593baecc87c64d1354cd5786975bd9 Mon Sep 17 00:00:00 2001
From: Maxim Levitsky <mlevitsk@redhat.com>
Date: Mon, 6 Jun 2022 21:11:49 +0300
Subject: [PATCH] KVM: SVM: fix tsc scaling cache logic
SVM uses a per-cpu variable to cache the current value of the
tsc scaling multiplier msr on each cpu.
Commit 1ab9287add5e2
("KVM: X86: Add vendor callbacks for writing the TSC multiplier")
broke this caching logic.
Refactor the code so that all TSC scaling multiplier writes go through
a single function which checks and updates the cache.
This fixes the following scenario:
1. A CPU runs a guest with some tsc scaling ratio.
2. New guest with different tsc scaling ratio starts on this CPU
and terminates almost immediately.
This ensures that the short running guest had set the tsc scaling ratio just
once when it was set via KVM_SET_TSC_KHZ. Due to the bug,
the per-cpu cache is not updated.
3. The original guest continues to run, it doesn't restore the msr
value back to its own value, because the cache matches,
and thus continues to run with a wrong tsc scaling ratio.
Fixes: 1ab9287add5e2 ("KVM: X86: Add vendor callbacks for writing the TSC multiplier")
Signed-off-by: Maxim Levitsky <mlevitsk@redhat.com>
Message-Id: <20220606181149.103072-1-mlevitsk@redhat.com>
Cc: stable@vger.kernel.org
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
[FE: backport, mainly dropped parts for the not yet present
5228eb96a487 ("KVM: x86: nSVM: implement nested TSC scaling")]
Signed-off-by: Fiona Ebner <f.ebner@proxmox.com>
---
arch/x86/kvm/svm/svm.c | 30 +++++++++++++++++++-----------
1 file changed, 19 insertions(+), 11 deletions(-)
diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
index 938b9b24f0ee..ea87d06bdaba 100644
--- a/arch/x86/kvm/svm/svm.c
+++ b/arch/x86/kvm/svm/svm.c
@@ -468,11 +468,24 @@ static int has_svm(void)
return 1;
}
+void __svm_write_tsc_multiplier(u64 multiplier)
+{
+ preempt_disable();
+
+ if (multiplier == __this_cpu_read(current_tsc_ratio))
+ goto out;
+
+ wrmsrl(MSR_AMD64_TSC_RATIO, multiplier);
+ __this_cpu_write(current_tsc_ratio, multiplier);
+out:
+ preempt_enable();
+}
+
static void svm_hardware_disable(void)
{
/* Make sure we clean up behind us */
if (static_cpu_has(X86_FEATURE_TSCRATEMSR))
- wrmsrl(MSR_AMD64_TSC_RATIO, TSC_RATIO_DEFAULT);
+ __svm_write_tsc_multiplier(TSC_RATIO_DEFAULT);
cpu_svm_disable();
@@ -514,8 +527,7 @@ static int svm_hardware_enable(void)
wrmsrl(MSR_VM_HSAVE_PA, __sme_page_pa(sd->save_area));
if (static_cpu_has(X86_FEATURE_TSCRATEMSR)) {
- wrmsrl(MSR_AMD64_TSC_RATIO, TSC_RATIO_DEFAULT);
- __this_cpu_write(current_tsc_ratio, TSC_RATIO_DEFAULT);
+ __svm_write_tsc_multiplier(TSC_RATIO_DEFAULT);
}
@@ -1128,9 +1140,10 @@ static void svm_write_tsc_offset(struct kvm_vcpu *vcpu, u64 offset)
static void svm_write_tsc_multiplier(struct kvm_vcpu *vcpu, u64 multiplier)
{
- wrmsrl(MSR_AMD64_TSC_RATIO, multiplier);
+ __svm_write_tsc_multiplier(multiplier);
}
+
/* Evaluate instruction intercepts that depend on guest CPUID features. */
static void svm_recalc_instruction_intercepts(struct kvm_vcpu *vcpu,
struct vcpu_svm *svm)
@@ -1453,13 +1466,8 @@ static void svm_prepare_guest_switch(struct kvm_vcpu *vcpu)
vmsave(__sme_page_pa(sd->save_area));
}
- if (static_cpu_has(X86_FEATURE_TSCRATEMSR)) {
- u64 tsc_ratio = vcpu->arch.tsc_scaling_ratio;
- if (tsc_ratio != __this_cpu_read(current_tsc_ratio)) {
- __this_cpu_write(current_tsc_ratio, tsc_ratio);
- wrmsrl(MSR_AMD64_TSC_RATIO, tsc_ratio);
- }
- }
+ if (static_cpu_has(X86_FEATURE_TSCRATEMSR))
+ __svm_write_tsc_multiplier(vcpu->arch.tsc_scaling_ratio);
if (likely(tsc_aux_uret_slot >= 0))
kvm_set_user_return_msr(tsc_aux_uret_slot, svm->tsc_aux, -1ull);
--
2.30.2