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From:   Paolo Bonzini <pbonzini@redhat.com>
Date:   Mon, 30 Oct 2023 18:00:49 +0100
Message-ID: <CABgObfYM4nyb1K3xJVGvV+eQmZoLPAmz2-=1CG8++pCwvVW7Qg@mail.gmail.com>
Subject: Re: [PATCH v13 03/35] KVM: Use gfn instead of hva for mmu_notifier_retry
To:     David Matlack <dmatlack@google.com>
Cc:     Sean Christopherson <seanjc@google.com>,
        Marc Zyngier <maz@kernel.org>,
        Oliver Upton <oliver.upton@linux.dev>,
        Huacai Chen <chenhuacai@kernel.org>,
        Michael Ellerman <mpe@ellerman.id.au>,
        Anup Patel <anup@brainfault.org>,
        Paul Walmsley <paul.walmsley@sifive.com>,
        Palmer Dabbelt <palmer@dabbelt.com>,
        Albert Ou <aou@eecs.berkeley.edu>,
        Alexander Viro <viro@zeniv.linux.org.uk>,
        Christian Brauner <brauner@kernel.org>,
        "Matthew Wilcox (Oracle)" <willy@infradead.org>,
        Andrew Morton <akpm@linux-foundation.org>, kvm@vger.kernel.org,
        linux-arm-kernel@lists.infradead.org, kvmarm@lists.linux.dev,
        linux-mips@vger.kernel.org, linuxppc-dev@lists.ozlabs.org,
        kvm-riscv@lists.infradead.org, linux-riscv@lists.infradead.org,
        linux-fsdevel@vger.kernel.org, linux-mm@kvack.org,
        linux-kernel@vger.kernel.org, Xiaoyao Li <xiaoyao.li@intel.com>,
        Xu Yilun <yilun.xu@intel.com>,
        Chao Peng <chao.p.peng@linux.intel.com>,
        Fuad Tabba <tabba@google.com>,
        Jarkko Sakkinen <jarkko@kernel.org>,
        Anish Moorthy <amoorthy@google.com>,
        Yu Zhang <yu.c.zhang@linux.intel.com>,
        Isaku Yamahata <isaku.yamahata@intel.com>,
        =?UTF-8?B?TWlja2HDq2wgU2FsYcO8bg==?= <mic@digikod.net>,
        Vlastimil Babka <vbabka@suse.cz>,
        Vishal Annapurve <vannapurve@google.com>,
        Ackerley Tng <ackerleytng@google.com>,
        Maciej Szmigiero <mail@maciej.szmigiero.name>,
        David Hildenbrand <david@redhat.com>,
        Quentin Perret <qperret@google.com>,
        Michael Roth <michael.roth@amd.com>,
        Wang <wei.w.wang@intel.com>,
        Liam Merwick <liam.merwick@oracle.com>,
        Isaku Yamahata <isaku.yamahata@gmail.com>,
        "Kirill A . Shutemov" <kirill.shutemov@linux.intel.com>
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On Mon, Oct 30, 2023 at 5:53=E2=80=AFPM David Matlack <dmatlack@google.com>=
 wrote:
>
> On 2023-10-27 11:21 AM, Sean Christopherson wrote:
> > From: Chao Peng <chao.p.peng@linux.intel.com>
> >
> > Currently in mmu_notifier invalidate path, hva range is recorded and
> > then checked against by mmu_notifier_retry_hva() in the page fault
> > handling path. However, for the to be introduced private memory, a page
>                           ^^^^^^^^^^^^^^^^^^^^^^^^
>
> Is there a missing word here?

No but there could be missing hyphens ("for the to-be-introduced
private memory"); possibly a "soon" could help parsing and that is
what you were talking about?

> >       if (likely(kvm->mmu_invalidate_in_progress =3D=3D 1)) {
> > +             kvm->mmu_invalidate_range_start =3D INVALID_GPA;
> > +             kvm->mmu_invalidate_range_end =3D INVALID_GPA;
>
> I don't think this is incorrect, but I was a little suprised to see this
> here rather than in end() when mmu_invalidate_in_progress decrements to
> 0.

I think that would be incorrect on the very first start?

> > +     }
> > +}
> > +
> > +void kvm_mmu_invalidate_range_add(struct kvm *kvm, gfn_t start, gfn_t =
end)
> > +{
> > +     lockdep_assert_held_write(&kvm->mmu_lock);
>
> Does this compile/function on KVM architectures with
> !KVM_HAVE_MMU_RWLOCK?

Yes:

#define lockdep_assert_held_write(l)    \
        lockdep_assert(lockdep_is_held_type(l, 0))

where 0 is the lock-held type used by lock_acquire_exclusive. In turn
is what you get for a spinlock or mutex, in addition to a rwlock or
rwsem that is taken for write.

Instead, lockdep_assert_held() asserts that the lock is taken without
asserting a particular lock-held type.

> > @@ -834,6 +851,12 @@ void kvm_mmu_invalidate_end(struct kvm *kvm, unsig=
ned long start,
>
> Let's add a lockdep_assert_held_write(&kvm->mmu_lock) here too while
> we're at it?

Yes, good idea.

Paolo