Re: [PATCH v2 2/4] KVM: hyper-v: Collect hypercall params into struct

[Siddharth Chandrasekaran]

On Tue, Apr 13, 2021 at 03:53:01PM +0200, Vitaly Kuznetsov wrote:
> Siddharth Chandrasekaran <sidcha@xxxxxxxxx> writes:
> > As of now there are 7 parameters (and flags) that are used in various
> > hyper-v hypercall handlers. There are 6 more input/output parameters
> > passed from XMM registers which are to be added in an upcoming patch.
> >
> > To make passing arguments to the handlers more readable, capture all
> > these parameters into a single structure.
> >
> > Cc: Alexander Graf <graf@xxxxxxxxxx>
> > Cc: Evgeny Iakovlev <eyakovl@xxxxxxxxx>
> > Signed-off-by: Siddharth Chandrasekaran <sidcha@xxxxxxxxx>
> > ---
> >  arch/x86/kvm/hyperv.c | 147 +++++++++++++++++++++++-------------------
> >  1 file changed, 79 insertions(+), 68 deletions(-)
> >
> > diff --git a/arch/x86/kvm/hyperv.c b/arch/x86/kvm/hyperv.c
> > index f98370a39936..8f6babd1ea0d 100644
> > --- a/arch/x86/kvm/hyperv.c
> > +++ b/arch/x86/kvm/hyperv.c
> > @@ -1623,7 +1623,18 @@ static __always_inline unsigned long *sparse_set_to_vcpu_mask(
> >       return vcpu_bitmap;
> >  }
> >
> > -static u64 kvm_hv_flush_tlb(struct kvm_vcpu *vcpu, u64 ingpa, u16 rep_cnt, bool ex)
> > +struct kvm_hv_hcall {
> > +     u64 param;
> > +     u64 ingpa;
> > +     u64 outgpa;
> > +     u16 code;
> > +     u16 rep_cnt;
> > +     u16 rep_idx;
> > +     bool fast;
> > +     bool rep;
> > +};
> > +
> > +static u64 kvm_hv_flush_tlb(struct kvm_vcpu *vcpu, struct kvm_hv_hcall *hc, bool ex)
> 
> Nitpick: Would it make sense to also pack the fact that we're dealing
> with a hypercall using ExProcessorMasks into 'struct kvm_hv_hcall' and
> get rid of 'bool ex' parameter for both kvm_hv_flush_tlb() and
> kvm_hv_send_ipi()? 'struct kvm_hv_hcall' is already a synthetic
> aggregator for input and output so adding some other information there
> may not be that big of a stretch...

The other members of the struct are all hypercall parameters (or flags)
while the 'bool ex' is our way of handling ExProcessorMasks within the
same method.

Besides, in kvm_hv_hypercall() passing it as a 3rd argument looks
better than setting 'hc.ex = true' and than immediately calling the
method :-).

> >  {
> >       struct kvm *kvm = vcpu->kvm;
> >       struct kvm_vcpu_hv *hv_vcpu = to_hv_vcpu(vcpu);
> > @@ -1638,7 +1649,7 @@ static u64 kvm_hv_flush_tlb(struct kvm_vcpu *vcpu, u64 ingpa, u16 rep_cnt, bool
> >       bool all_cpus;
> >
> >       if (!ex) {
> > -             if (unlikely(kvm_read_guest(kvm, ingpa, &flush, sizeof(flush))))
> > +             if (unlikely(kvm_read_guest(kvm, hc->ingpa, &flush, sizeof(flush))))
> >                       return HV_STATUS_INVALID_HYPERCALL_INPUT;
> >
> >               trace_kvm_hv_flush_tlb(flush.processor_mask,
> > @@ -1657,7 +1668,7 @@ static u64 kvm_hv_flush_tlb(struct kvm_vcpu *vcpu, u64 ingpa, u16 rep_cnt, bool
> >               all_cpus = (flush.flags & HV_FLUSH_ALL_PROCESSORS) ||
> >                       flush.processor_mask == 0;
> >       } else {
> > -             if (unlikely(kvm_read_guest(kvm, ingpa, &flush_ex,
> > +             if (unlikely(kvm_read_guest(kvm, hc->ingpa, &flush_ex,
> >                                           sizeof(flush_ex))))
> >                       return HV_STATUS_INVALID_HYPERCALL_INPUT;
> >
> > @@ -1679,8 +1690,8 @@ static u64 kvm_hv_flush_tlb(struct kvm_vcpu *vcpu, u64 ingpa, u16 rep_cnt, bool
> >
> >               if (!all_cpus &&
> >                   kvm_read_guest(kvm,
> > -                                ingpa + offsetof(struct hv_tlb_flush_ex,
> > -                                                 hv_vp_set.bank_contents),
> > +                                hc->ingpa + offsetof(struct hv_tlb_flush_ex,
> > +                                                     hv_vp_set.bank_contents),
> >                                  sparse_banks,
> >                                  sparse_banks_len))
> >                       return HV_STATUS_INVALID_HYPERCALL_INPUT;
> > @@ -1700,9 +1711,9 @@ static u64 kvm_hv_flush_tlb(struct kvm_vcpu *vcpu, u64 ingpa, u16 rep_cnt, bool
> >                                   NULL, vcpu_mask, &hv_vcpu->tlb_flush);
> >
> >  ret_success:
> > -     /* We always do full TLB flush, set rep_done = rep_cnt. */
> > +     /* We always do full TLB flush, set rep_done = hc->rep_cnt. */
> 
> Nitpicking: I'd suggest we word it a bit differently:
> 
> "We always do full TLB flush, set 'Reps completed' = 'Rep Count'."
> 
> so it matches TLFS rather than KVM internals.

Makes sense. Changed.

Thanks for your reviews.

~ Sid.



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