Re: [RFC PATCH 3/6] KVM: Define kvm_flush_remote_tlbs_range

[Raghavendra Rao Ananta]

On Mon, Jan 9, 2023 at 3:41 PM David Matlack <dmatlack@xxxxxxxxxx> wrote:
>
> On Mon, Jan 09, 2023 at 09:53:44PM +0000, Raghavendra Rao Ananta wrote:
> > Define kvm_flush_remote_tlbs_range() to limit the TLB flush only
> > to a certain range of addresses. Replace this with the existing
> > call to kvm_flush_remote_tlbs() in the MMU notifier path.
> > Architectures such as arm64 can define this to flush only the
> > necessary addresses, instead of the entire range.
> >
> > Signed-off-by: Raghavendra Rao Ananta <rananta@xxxxxxxxxx>
> > ---
> >  arch/arm64/kvm/mmu.c     | 10 ++++++++++
> >  include/linux/kvm_host.h |  1 +
> >  virt/kvm/kvm_main.c      |  7 ++++++-
> >  3 files changed, 17 insertions(+), 1 deletion(-)
> >
> > diff --git a/arch/arm64/kvm/mmu.c b/arch/arm64/kvm/mmu.c
> > index 39d9a334efb57..70f76bc909c5d 100644
> > --- a/arch/arm64/kvm/mmu.c
> > +++ b/arch/arm64/kvm/mmu.c
> > @@ -91,6 +91,16 @@ void kvm_flush_remote_tlbs(struct kvm *kvm)
> >       kvm_call_hyp(__kvm_tlb_flush_vmid, &kvm->arch.mmu);
> >  }
> >
> > +void kvm_flush_remote_tlbs_range(struct kvm *kvm, unsigned long start, unsigned long end)
> > +{
> > +     struct kvm_s2_mmu *mmu = &kvm->arch.mmu;
> > +
> > +     if (system_supports_tlb_range())
> > +             kvm_call_hyp(__kvm_tlb_flush_range_vmid_ipa, mmu, start, end, 0);
> > +     else
> > +             kvm_flush_remote_tlbs(kvm);
> > +}
> > +
> >  static bool kvm_is_device_pfn(unsigned long pfn)
> >  {
> >       return !pfn_is_map_memory(pfn);
> > diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
> > index f51eb9419bfc3..a76cede9dc3bb 100644
> > --- a/include/linux/kvm_host.h
> > +++ b/include/linux/kvm_host.h
> > @@ -1359,6 +1359,7 @@ int kvm_vcpu_yield_to(struct kvm_vcpu *target);
> >  void kvm_vcpu_on_spin(struct kvm_vcpu *vcpu, bool usermode_vcpu_not_eligible);
> >
> >  void kvm_flush_remote_tlbs(struct kvm *kvm);
> > +void kvm_flush_remote_tlbs_range(struct kvm *kvm, unsigned long start, unsigned long end);
> >
> >  #ifdef KVM_ARCH_NR_OBJS_PER_MEMORY_CACHE
> >  int kvm_mmu_topup_memory_cache(struct kvm_mmu_memory_cache *mc, int min);
> > diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
> > index 03e6a38094c17..f538ecc984f5b 100644
> > --- a/virt/kvm/kvm_main.c
> > +++ b/virt/kvm/kvm_main.c
> > @@ -376,6 +376,11 @@ void kvm_flush_remote_tlbs(struct kvm *kvm)
> >               ++kvm->stat.generic.remote_tlb_flush;
> >  }
> >  EXPORT_SYMBOL_GPL(kvm_flush_remote_tlbs);
> > +
> > +void kvm_flush_remote_tlbs_range(struct kvm *kvm, unsigned long start, unsigned long end)
>
> It's ambiguous what start/end represent. Case in point,
> __kvm_handle_hva_range() is passing in HVAs but then patch 4 passes in
> GFNs.
>
> Probably kvm_flush_tlbs_range() should accept GFN and there can be a
> helper wrapper that does the HVA-to-GFN conversion.
>
> > +{
> > +     kvm_flush_remote_tlbs(kvm);
> > +}
>
You are right, that should've been GFNs, and the function should
operate on GPAs. I can think about a wrapper.

> FYI I also proposed a common kvm_flush_remote_tlbs() in my Common MMU
> series [1].
>
> Could I interest you in grabbing patches 29-33 from that series, which
> has the same end result (common kvm_flush_remote_tlbs_range()) but also
> hooks up the KVM/x86 range-based flushing, and folding them into this
> series?
>
Of course! I'll grab them in my next version.

Thank you.
Raghavendra

> [1] https://lore.kernel.org/kvm/20221208193857.4090582-33-dmatlack@xxxxxxxxxx/
>
> >  #endif
> >
> >  static void kvm_flush_shadow_all(struct kvm *kvm)
> > @@ -637,7 +642,7 @@ static __always_inline int __kvm_handle_hva_range(struct kvm *kvm,
> >       }
> >
> >       if (range->flush_on_ret && ret)
> > -             kvm_flush_remote_tlbs(kvm);
> > +             kvm_flush_remote_tlbs_range(kvm, range->start, range->end - 1);
> >
> >       if (locked) {
> >               KVM_MMU_UNLOCK(kvm);
> > --
> > 2.39.0.314.g84b9a713c41-goog
> >