From: Sean Christopherson <seanjc@google.com>
To: "Stamatis, Ilias" <ilstam@amazon.com>
Cc: "kvm@vger.kernel.org" <kvm@vger.kernel.org>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
"jmattson@google.com" <jmattson@google.com>,
"Woodhouse, David" <dwmw@amazon.co.uk>,
"vkuznets@redhat.com" <vkuznets@redhat.com>,
"joro@8bytes.org" <joro@8bytes.org>,
"mtosatti@redhat.com" <mtosatti@redhat.com>,
"zamsden@gmail.com" <zamsden@gmail.com>,
"pbonzini@redhat.com" <pbonzini@redhat.com>,
"mlevitsk@redhat.com" <mlevitsk@redhat.com>,
"wanpengli@tencent.com" <wanpengli@tencent.com>
Subject: Re: [PATCH v2 07/10] KVM: X86: Move write_l1_tsc_offset() logic to common code and rename it
Date: Wed, 19 May 2021 15:49:07 +0000 [thread overview]
Message-ID: <YKUzc4WJlxvyzw5B@google.com> (raw)
In-Reply-To: <e9f32ea05762ad8b87b1f8e6821ca2c8a4077bbc.camel@amazon.com>
On Wed, May 19, 2021, Stamatis, Ilias wrote:
> On Wed, 2021-05-19 at 00:05 +0000, Sean Christopherson wrote:
> > On Wed, May 12, 2021, Ilias Stamatis wrote:
> > > diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> > > index 1db6cfc2079f..f3ba1be4d5b9 100644
> > > --- a/arch/x86/kvm/x86.c
> > > +++ b/arch/x86/kvm/x86.c
> > > @@ -2377,8 +2377,23 @@ EXPORT_SYMBOL_GPL(kvm_set_02_tsc_multiplier);
> > >
> > > static void kvm_vcpu_write_tsc_offset(struct kvm_vcpu *vcpu, u64 offset)
> > > {
> > > + trace_kvm_write_tsc_offset(vcpu->vcpu_id,
> > > + vcpu->arch.l1_tsc_offset,
> > > + offset);
> > > +
> > > vcpu->arch.l1_tsc_offset = offset;
> > > - vcpu->arch.tsc_offset = static_call(kvm_x86_write_l1_tsc_offset)(vcpu, offset);
> > > + vcpu->arch.tsc_offset = offset;
> > > +
> > > + if (is_guest_mode(vcpu)) {
> >
> > Unnecessary curly braces.
>
> Really? We are supposed to have a 6-lines body without brackets? I'm not
> opposing, I'm just surprised that that's the coding standard.
Comments don't (technically) count. I usually avoid the ambiguity by putting
the comment above the if statement. That also helps with indentation, e.g.
/*
* This is a comment.
*/
if (is_guest_mode(vcpu))
kvm_set_02_tsc_offset(vcpu);
> > > + /*
> > > + * We're here if L1 chose not to trap WRMSR to TSC and
> > > + * according to the spec this should set L1's TSC (as opposed
> > > + * to setting L1's offset for L2).
> > > + */
> >
> > While we're shuffling code, can we improve this comment? It works for the WRMSR
> > case, but makes no sense in the context of host TSC adjustments. It's not at all
> > clear to me that it's even correct or relevant in those cases.
> >
>
> Do you suggest removing it completely or how do you want it to be? I don't
> mind deleting it.
Heh, I'd happily write the comment, except I have no idea what the logic is in
the non-WRMSR case. I do think we need a comment, IMO none of paths that lead
to changing the TSC offset while L2 is active are obvious.
next prev parent reply other threads:[~2021-05-19 15:49 UTC|newest]
Thread overview: 25+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-05-12 15:09 [PATCH v2 00/10] KVM: Implement nested TSC scaling Ilias Stamatis
2021-05-12 15:09 ` [PATCH v2 01/10] math64.h: Add mul_s64_u64_shr() Ilias Stamatis
2021-05-18 22:36 ` Sean Christopherson
2021-05-12 15:09 ` [PATCH v2 02/10] KVM: X86: Store L1's TSC scaling ratio in 'struct kvm_vcpu_arch' Ilias Stamatis
2021-05-18 22:52 ` Sean Christopherson
2021-05-19 8:54 ` Stamatis, Ilias
2021-05-12 15:09 ` [PATCH v2 03/10] KVM: X86: Add kvm_scale_tsc_l1() and kvm_compute_tsc_offset_l1() Ilias Stamatis
2021-05-18 23:04 ` Sean Christopherson
2021-05-19 9:02 ` Stamatis, Ilias
2021-05-19 15:40 ` Sean Christopherson
2021-05-20 18:27 ` Stamatis, Ilias
2021-05-12 15:09 ` [PATCH v2 04/10] KVM: VMX: Add a TSC multiplier field in VMCS12 Ilias Stamatis
2021-05-12 15:09 ` [PATCH v2 05/10] KVM: X86: Add functions for retrieving L2 TSC fields from common code Ilias Stamatis
2021-05-12 15:09 ` [PATCH v2 06/10] KVM: X86: Add functions that calculate the 02 TSC offset and multiplier Ilias Stamatis
2021-05-18 23:21 ` Sean Christopherson
2021-05-19 10:15 ` Stamatis, Ilias
2021-05-12 15:09 ` [PATCH v2 07/10] KVM: X86: Move write_l1_tsc_offset() logic to common code and rename it Ilias Stamatis
2021-05-19 0:05 ` Sean Christopherson
2021-05-19 11:45 ` Stamatis, Ilias
2021-05-19 15:49 ` Sean Christopherson [this message]
2021-05-12 15:09 ` [PATCH v2 08/10] KVM: VMX: Set the TSC offset and multiplier on nested entry and exit Ilias Stamatis
2021-05-19 0:07 ` Sean Christopherson
2021-05-19 11:55 ` Stamatis, Ilias
2021-05-12 15:09 ` [PATCH v2 09/10] KVM: VMX: Expose TSC scaling to L2 Ilias Stamatis
2021-05-12 15:09 ` [PATCH v2 10/10] KVM: selftests: x86: Add vmx_nested_tsc_scaling_test Ilias Stamatis
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