2014-11-13 03:01:12

by Chris J Arges

Subject: [PATCH] kvm: svm: move WARN_ON in svm_adjust_tsc_offset

When running the tsc_adjust kvm-unit-test on an AMD processor with the
IA32_TSC_ADJUST feature enabled, the WARN_ON in svm_adjust_tsc_offset can be
triggered. This WARN_ON checks for a negative adjustment in case __scale_tsc
is called; however it may trigger unnecessary warnings.

This patch moves the WARN_ON to trigger only if __scale_tsc will actually be
called from svm_adjust_tsc_offset. In addition make adj in kvm_set_msr_common
s64 since this can have signed values.

Signed-off-by: Chris J Arges <[email protected]>
---
arch/x86/kvm/svm.c | 8 +++++---
arch/x86/kvm/x86.c | 2 +-
2 files changed, 6 insertions(+), 4 deletions(-)

diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c
index d4f3aaa..6b411ad 100644
--- a/arch/x86/kvm/svm.c
+++ b/arch/x86/kvm/svm.c
@@ -1056,9 +1056,11 @@ static void svm_adjust_tsc_offset(struct kvm_vcpu *vcpu, s64 adjustment, bool ho
{
struct vcpu_svm *svm = to_svm(vcpu);

- WARN_ON(adjustment < 0);
- if (host)
- adjustment = svm_scale_tsc(vcpu, adjustment);
+ if (host) {
+ if (svm->tsc_ratio != TSC_RATIO_DEFAULT)
+ WARN_ON(adjustment < 0);
+ adjustment = svm_scale_tsc(vcpu, (u64)adjustment);
+ }

svm->vmcb->control.tsc_offset += adjustment;
if (is_guest_mode(vcpu))
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index f85da5c..1cd1376 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -2141,7 +2141,7 @@ int kvm_set_msr_common(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
case MSR_IA32_TSC_ADJUST:
if (guest_cpuid_has_tsc_adjust(vcpu)) {
if (!msr_info->host_initiated) {
- u64 adj = data - vcpu->arch.ia32_tsc_adjust_msr;
+ s64 adj = data - vcpu->arch.ia32_tsc_adjust_msr;
kvm_x86_ops->adjust_tsc_offset(vcpu, adj, true);
}
vcpu->arch.ia32_tsc_adjust_msr = data;
--
1.9.1

2014-11-13 10:56:35

by Paolo Bonzini

Subject: Re: [PATCH] kvm: svm: move WARN_ON in svm_adjust_tsc_offset

On 13/11/2014 04:00, Chris J Arges wrote:
> When running the tsc_adjust kvm-unit-test on an AMD processor with the
> IA32_TSC_ADJUST feature enabled, the WARN_ON in svm_adjust_tsc_offset can be
> triggered. This WARN_ON checks for a negative adjustment in case __scale_tsc
> is called; however it may trigger unnecessary warnings.
>
> This patch moves the WARN_ON to trigger only if __scale_tsc will actually be
> called from svm_adjust_tsc_offset. In addition make adj in kvm_set_msr_common
> s64 since this can have signed values.
>
> Signed-off-by: Chris J Arges <[email protected]>
> ---
> arch/x86/kvm/svm.c | 8 +++++---
> arch/x86/kvm/x86.c | 2 +-
> 2 files changed, 6 insertions(+), 4 deletions(-)
>
> diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c
> index d4f3aaa..6b411ad 100644
> --- a/arch/x86/kvm/svm.c
> +++ b/arch/x86/kvm/svm.c
> @@ -1056,9 +1056,11 @@ static void svm_adjust_tsc_offset(struct kvm_vcpu *vcpu, s64 adjustment, bool ho
> {
> struct vcpu_svm *svm = to_svm(vcpu);
>
> - WARN_ON(adjustment < 0);
> - if (host)
> - adjustment = svm_scale_tsc(vcpu, adjustment);
> + if (host) {
> + if (svm->tsc_ratio != TSC_RATIO_DEFAULT)
> + WARN_ON(adjustment < 0);
> + adjustment = svm_scale_tsc(vcpu, (u64)adjustment);
> + }
>
> svm->vmcb->control.tsc_offset += adjustment;
> if (is_guest_mode(vcpu))
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index f85da5c..1cd1376 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -2141,7 +2141,7 @@ int kvm_set_msr_common(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
> case MSR_IA32_TSC_ADJUST:
> if (guest_cpuid_has_tsc_adjust(vcpu)) {
> if (!msr_info->host_initiated) {
> - u64 adj = data - vcpu->arch.ia32_tsc_adjust_msr;
> + s64 adj = data - vcpu->arch.ia32_tsc_adjust_msr;
> kvm_x86_ops->adjust_tsc_offset(vcpu, adj, true);
> }
> vcpu->arch.ia32_tsc_adjust_msr = data;
>

Applied, thanks!

Paolo