linux-kernel - Re: [PATCH v4 3/6] KVM: arm64: Implement kvm_arch_flush_remote_tlbs

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Message-ID: <CAJHc60x0iFWOFxcCYpH6bG+CinBM2TmYxvADKwOqDsUFJCr0AA@mail.gmail.com>
Date:   Tue, 30 May 2023 14:22:23 -0700
From:   Raghavendra Rao Ananta <rananta@...gle.com>
To:     Marc Zyngier <maz@...nel.org>
Cc:     Oliver Upton <oliver.upton@...ux.dev>,
        James Morse <james.morse@....com>,
        Suzuki K Poulose <suzuki.poulose@....com>,
        Ricardo Koller <ricarkol@...gle.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Jing Zhang <jingzhangos@...gle.com>,
        Colton Lewis <coltonlewis@...gle.com>,
        linux-arm-kernel@...ts.infradead.org, kvmarm@...ts.linux.dev,
        linux-kernel@...r.kernel.org, kvm@...r.kernel.org
Subject: Re: [PATCH v4 3/6] KVM: arm64: Implement kvm_arch_flush_remote_tlbs_range()

On Mon, May 29, 2023 at 7:00 AM Marc Zyngier <maz@...nel.org> wrote:
>
> On Fri, 19 May 2023 01:52:28 +0100,
> Raghavendra Rao Ananta <rananta@...gle.com> wrote:
> >
> > Implement kvm_arch_flush_remote_tlbs_range() for arm64
> > to invalidate the given range in the TLB.
> >
> > Signed-off-by: Raghavendra Rao Ananta <rananta@...gle.com>
> > ---
> >  arch/arm64/include/asm/kvm_host.h |  3 +++
> >  arch/arm64/kvm/hyp/nvhe/tlb.c     |  4 +---
> >  arch/arm64/kvm/mmu.c              | 11 +++++++++++
> >  3 files changed, 15 insertions(+), 3 deletions(-)
> >
> > diff --git a/arch/arm64/include/asm/kvm_host.h b/arch/arm64/include/asm/kvm_host.h
> > index 81ab41b84f436..343fb530eea9c 100644
> > --- a/arch/arm64/include/asm/kvm_host.h
> > +++ b/arch/arm64/include/asm/kvm_host.h
> > @@ -1081,6 +1081,9 @@ struct kvm *kvm_arch_alloc_vm(void);
> >  #define __KVM_HAVE_ARCH_FLUSH_REMOTE_TLBS
> >  int kvm_arch_flush_remote_tlbs(struct kvm *kvm);
> >
> > +#define __KVM_HAVE_ARCH_FLUSH_REMOTE_TLBS_RANGE
> > +int kvm_arch_flush_remote_tlbs_range(struct kvm *kvm, gfn_t start_gfn, u64 pages);
> > +
> >  static inline bool kvm_vm_is_protected(struct kvm *kvm)
> >  {
> >       return false;
> > diff --git a/arch/arm64/kvm/hyp/nvhe/tlb.c b/arch/arm64/kvm/hyp/nvhe/tlb.c
> > index d4ea549c4b5c4..d2c7c1bc6d441 100644
> > --- a/arch/arm64/kvm/hyp/nvhe/tlb.c
> > +++ b/arch/arm64/kvm/hyp/nvhe/tlb.c
> > @@ -150,10 +150,8 @@ void __kvm_tlb_flush_vmid_range(struct kvm_s2_mmu *mmu,
> >               return;
> >       }
> >
> > -     dsb(ishst);
> > -
> >       /* Switch to requested VMID */
> > -     __tlb_switch_to_guest(mmu, &cxt);
> > +     __tlb_switch_to_guest(mmu, &cxt, false);
>
> This hunk is in the wrong patch, isn't it?
>
Ah, you are right. It should be part of the previous patch. I think I
introduced it accidentally when I rebased the series. I'll remove it
in the next spin.


> >
> >       __flush_tlb_range_op(ipas2e1is, start, pages, stride, 0, 0, false);
> >
> > diff --git a/arch/arm64/kvm/mmu.c b/arch/arm64/kvm/mmu.c
> > index d0a0d3dca9316..e3673b4c10292 100644
> > --- a/arch/arm64/kvm/mmu.c
> > +++ b/arch/arm64/kvm/mmu.c
> > @@ -92,6 +92,17 @@ int kvm_arch_flush_remote_tlbs(struct kvm *kvm)
> >       return 0;
> >  }
> >
> > +int kvm_arch_flush_remote_tlbs_range(struct kvm *kvm, gfn_t start_gfn, u64 pages)
> > +{
> > +     phys_addr_t start, end;
> > +
> > +     start = start_gfn << PAGE_SHIFT;
> > +     end = (start_gfn + pages) << PAGE_SHIFT;
> > +
> > +     kvm_call_hyp(__kvm_tlb_flush_vmid_range, &kvm->arch.mmu, start, end);
>
> So that's the point that I think is not right. It is the MMU code that
> should drive the invalidation method, and not the HYP code. The HYP
> code should be as dumb as possible, and the logic should be kept in
> the MMU code.
>
> So when a range invalidation is forwarded to HYP, it's a *valid* range
> invalidation. not something that can fallback to VMID-wide invalidation.
>
I'm guessing that you are referring to patch-2. Do you recommend
moving the 'pages >= MAX_TLBI_RANGE_PAGES' logic here and simply
return an error? How about for the other check:
system_supports_tlb_range()?
The idea was for __kvm_tlb_flush_vmid_range() to also implement a
fallback mechanism in case the system doesn't support the range-based
instructions. But if we end up calling __kvm_tlb_flush_vmid_range()
from multiple cases, we'd end up duplicating the checks. WDYT?


> Thanks,
>
>         M.
>
> --
> Without deviation from the norm, progress is not possible.