linux-kernel - Re: [RFC PATCH v12 02/33] KVM: Use gfn instead of hva for mmu_notifier

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Message-ID: <ZQr5uXhV6Cnx4DYT@google.com>
Date:   Wed, 20 Sep 2023 06:55:05 -0700
From:   Sean Christopherson <seanjc@...gle.com>
To:     Xu Yilun <yilun.xu@...el.com>
Cc:     Paolo Bonzini <pbonzini@...hat.com>, Marc Zyngier <maz@...nel.org>,
        Oliver Upton <oliver.upton@...ux.dev>,
        Huacai Chen <chenhuacai@...nel.org>,
        Michael Ellerman <mpe@...erman.id.au>,
        Anup Patel <anup@...infault.org>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        Palmer Dabbelt <palmer@...belt.com>,
        Albert Ou <aou@...s.berkeley.edu>,
        "Matthew Wilcox (Oracle)" <willy@...radead.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Paul Moore <paul@...l-moore.com>,
        James Morris <jmorris@...ei.org>,
        "Serge E. Hallyn" <serge@...lyn.com>, kvm@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, kvmarm@...ts.linux.dev,
        linux-mips@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
        kvm-riscv@...ts.infradead.org, linux-riscv@...ts.infradead.org,
        linux-fsdevel@...r.kernel.org, linux-mm@...ck.org,
        linux-security-module@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        Chao Peng <chao.p.peng@...ux.intel.com>,
        Fuad Tabba <tabba@...gle.com>,
        Jarkko Sakkinen <jarkko@...nel.org>,
        Anish Moorthy <amoorthy@...gle.com>,
        Yu Zhang <yu.c.zhang@...ux.intel.com>,
        Isaku Yamahata <isaku.yamahata@...el.com>,
        Vlastimil Babka <vbabka@...e.cz>,
        Vishal Annapurve <vannapurve@...gle.com>,
        Ackerley Tng <ackerleytng@...gle.com>,
        Maciej Szmigiero <mail@...iej.szmigiero.name>,
        David Hildenbrand <david@...hat.com>,
        Quentin Perret <qperret@...gle.com>,
        Michael Roth <michael.roth@....com>,
        Wang <wei.w.wang@...el.com>,
        Liam Merwick <liam.merwick@...cle.com>,
        Isaku Yamahata <isaku.yamahata@...il.com>,
        "Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>
Subject: Re: [RFC PATCH v12 02/33] KVM: Use gfn instead of hva for mmu_notifier_retry

On Wed, Sep 20, 2023, Xu Yilun wrote:
> On 2023-09-13 at 18:55:00 -0700, Sean Christopherson wrote:
> > +void kvm_mmu_invalidate_range_add(struct kvm *kvm, gfn_t start, gfn_t end)
> > +{
> > +	lockdep_assert_held_write(&kvm->mmu_lock);
> > +
> > +	WARN_ON_ONCE(!kvm->mmu_invalidate_in_progress);
> > +
> >  	if (likely(kvm->mmu_invalidate_in_progress == 1)) {
> >  		kvm->mmu_invalidate_range_start = start;
> >  		kvm->mmu_invalidate_range_end = end;
> 
> IIUC, Now we only add or override a part of the invalidate range in
> these fields, IOW only the range in last slot is stored when we unlock.

Ouch.  Good catch!

> That may break mmu_invalidate_retry_gfn() cause it can never know the
> whole invalidate range.
> 
> How about we extend the mmu_invalidate_range_start/end everytime so that
> it records the whole invalidate range:
> 
> if (kvm->mmu_invalidate_range_start == INVALID_GPA) {
> 	kvm->mmu_invalidate_range_start = start;
> 	kvm->mmu_invalidate_range_end = end;
> } else {
> 	kvm->mmu_invalidate_range_start =
> 		min(kvm->mmu_invalidate_range_start, start);
> 	kvm->mmu_invalidate_range_end =
> 		max(kvm->mmu_invalidate_range_end, end);
> }

Yeah, that does seem to be the easiest solution.

I'll post a fixup patch, unless you want the honors.