On Thu, Jul 31, 2025, Xin Li wrote:
> On 7/31/2025 3:34 AM, Chao Gao wrote:
> > > -fastpath_t handle_fastpath_set_msr_irqoff(struct kvm_vcpu *vcpu)
> > > +static fastpath_t handle_set_msr_irqoff(struct kvm_vcpu *vcpu, u32 msr, int reg)
> >
> > How about __handle_fastpath_set_msr_irqoff()? It's better to keep
> > "fastpath" in the function name to convey that this function is for
> > fastpath only.
>
> This is now a static function with return type fastpath_t, so I guess
> it's okay to remove fastpath from its name (It looks that Sean prefers
> shorter function names if they contains enough information).
>
> But if the protocol is to have "fastpath" in all fast path function
> names, I can change it.
I'm also greedy and want it both ways :-)
Spoiler alert, this is what I ended up with (completely untested at this point):
static fastpath_t __handle_fastpath_wrmsr(struct kvm_vcpu *vcpu, u32 msr,
u64 data)
switch (msr) {
case APIC_BASE_MSR + (APIC_ICR >> 4):
if (!lapic_in_kernel(vcpu) || !apic_x2apic_mode(vcpu->arch.apic) ||
kvm_x2apic_icr_write_fast(vcpu->arch.apic, data))
return EXIT_FASTPATH_NONE;
break;
case MSR_IA32_TSC_DEADLINE:
if (!kvm_can_use_hv_timer(vcpu))
return EXIT_FASTPATH_NONE;
kvm_set_lapic_tscdeadline_msr(vcpu, data);
break;
default:
return EXIT_FASTPATH_NONE;
}
trace_kvm_msr_write(msr, data);
if (!kvm_skip_emulated_instruction(vcpu))
return EXIT_FASTPATH_EXIT_USERSPACE;
return EXIT_FASTPATH_REENTER_GUEST;
}
fastpath_t handle_fastpath_wrmsr(struct kvm_vcpu *vcpu)
{
return __handle_fastpath_wrmsr(vcpu, kvm_rcx_read(vcpu),
kvm_read_edx_eax(vcpu));
}
EXPORT_SYMBOL_GPL(handle_fastpath_set_msr_irqoff);
fastpath_t handle_fastpath_wrmsr_imm(struct kvm_vcpu *vcpu, u32 msr, int reg)
{
return __handle_fastpath_wrmsr(vcpu, msr, kvm_register_read(vcpu, reg));
}
EXPORT_SYMBOL_GPL(handle_fastpath_set_msr_imm_irqoff);
> > > {
> > > - u32 msr = kvm_rcx_read(vcpu);
> > > u64 data;
> > > fastpath_t ret;
> > > bool handled;
> > > @@ -2174,11 +2190,19 @@ fastpath_t handle_fastpath_set_msr_irqoff(struct kvm_vcpu *vcpu)
> > >
> > > switch (msr) {
> > > case APIC_BASE_MSR + (APIC_ICR >> 4):
> > > - data = kvm_read_edx_eax(vcpu);
> > > + if (reg == VCPU_EXREG_EDX_EAX)
> > > + data = kvm_read_edx_eax(vcpu);
> > > + else
> > > + data = kvm_register_read(vcpu, reg);
> >
> > ...
> >
> > > +
> > > handled = !handle_fastpath_set_x2apic_icr_irqoff(vcpu, data);
> > > break;
> > > case MSR_IA32_TSC_DEADLINE:
> > > - data = kvm_read_edx_eax(vcpu);
> > > + if (reg == VCPU_EXREG_EDX_EAX)
> > > + data = kvm_read_edx_eax(vcpu);
> > > + else
> > > + data = kvm_register_read(vcpu, reg);
> > > +
> >
> > Hoist this chunk out of the switch clause to avoid duplication.
>
> I thought about it, but didn't do so because the original code doesn't read
> the MSR data from registers when a MSR is not being handled in the
> fast path, which saves some cycles in most cases.
Can you hold off on doing anything with this series? Mostly to save your time.
Long story short, I unexpectedly dove into the fastpath code this week while sorting
out an issue with the mediated PMU series, and I ended up with a series of patches
to clean things up for both the mediated PMU series and for this series.
With luck, I'll get the cleanups, the mediated PMU series, and a v2 of this series
posted tomorrow (I also have some feedback on VCPU_EXREG_EDX_EAX; we can avoid it
entirely without much fuss).
