On Mon, 17 Aug 2026 22:29:22 +0100,
Dongli Zhang <[email protected]> wrote:
>
>
>
> On Mon, Aug 17, 2026 1:42:20AM -0700, Marc Zyngier wrote:
> > On Sun, 16 Aug 2026 06:33:03 +0100,
> > Dongli Zhang <[email protected]> wrote:
[...]
> >> diff --git a/arch/arm64/kvm/pvtime.c b/arch/arm64/kvm/pvtime.c
> >> index 4ceabaa4c30b..000bf49cc0fd 100644
> >> --- a/arch/arm64/kvm/pvtime.c
> >> +++ b/arch/arm64/kvm/pvtime.c
> >> @@ -32,6 +32,11 @@ void kvm_update_stolen_time(struct kvm_vcpu *vcpu)
> >> srcu_read_unlock(&kvm->srcu, idx);
> >> }
> >>
> >> +void kvm_reset_stolen_time(struct kvm_vcpu *vcpu)
> >> +{
> >> + vcpu->arch.steal.last_steal = current->sched_info.run_delay;
> >> +}
> >> +
> >> long kvm_hypercall_pv_features(struct kvm_vcpu *vcpu)
> >> {
> >> u32 feature = smccc_get_arg1(vcpu);
> >
> > Why isn't this common code? I really don't see the point in making
> > this arch-specific code. I'd expect something like this (untested):
> >
> > diff --git a/arch/arm64/include/asm/kvm_host.h
> > b/arch/arm64/include/asm/kvm_host.h
> > index ace5801a592f..3fb77360af01 100644
> > --- a/arch/arm64/include/asm/kvm_host.h
> > +++ b/arch/arm64/include/asm/kvm_host.h
> > @@ -950,6 +950,8 @@ struct kvm_vcpu_arch {
> > pid_t pid;
> > };
> >
> > +#define kvm_arch_vcpu_last_steal(v) (v)->arch.steal.last_steal
> > +
> > /*
> > * Each 'flag' is composed of a comma-separated triplet:
> > *
> > diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
> > index 45e784462ec6..117aeb49231a 100644
> > --- a/virt/kvm/kvm_main.c
> > +++ b/virt/kvm/kvm_main.c
> > @@ -4459,6 +4459,9 @@ static long kvm_vcpu_ioctl(struct file *filp,
> > if (r)
> > break;
> >
> > + if (IS_ENABLED(CONFIG_HAVE_PV_STEAL_CLOCK_GEN))
> > + kvm_arch_vcpu_last_steal(vcpu) =
> > current->sched_info.run_delay;
> > +
> > newpid = get_task_pid(current, PIDTYPE_PID);
> > write_lock(&vcpu->pid_lock);
> > vcpu->pid = newpid;
> >
> > where each architecture that implements steal time provides an
> > accessor, and the core code is in charge of the adjustment.
> >
> > It also makes sure that we don't leave any architecture behind.
> >
> Or how about making it something like below?
>
> if (IS_ENABLED(CONFIG_HAVE_PV_STEAL_CLOCK_GEN))
> kvm_arch_vcpu_reset_last_steal(vcpu);
>
> That would still move the policy to common KVM code, while leaving the exact
> arch state to the architecture implementation.
I don't think architectures should have a say in this. Steal time, as
a PV service, should not involve the architectures at all. After all,
that's the whole point of a PV service: hypervisor-specific hacks that
do not fit in the architectural envelope.
Bonus points if you move the last_steal field in the main vcpu
structure instead of some arch-specific one.
> For x86, the hook can reset vcpu->arch.st.last_steal for regular KVM steal
> time.
> If we also decide to cover Xen runstate in this series, the same x86 hook can
> additionally reset vcpu->arch.xen.last_steal.
For arch-specific stuff, there is the pid change hook already.
M.
--
Without deviation from the norm, progress is not possible.
