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    SubjectRe: [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@kernel.org> wrote:
    >
    > On Fri, 19 May 2023 01:52:28 +0100,
    > Raghavendra Rao Ananta <rananta@google.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@google.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.

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