From: Isaku Yamahata <isaku.yamahata@gmail•com>
To: David Stevens <stevensd@chromium•org>
Cc: Marc Zyngier <maz@kernel•org>,
kvm@vger•kernel.org, Sean Christopherson <seanjc@google•com>,
linux-kernel@vger•kernel.org, Peter Xu <peterx@redhat•com>,
Yu Zhang <yu.c.zhang@linux•intel.com>,
linux-arm-kernel@lists•infradead.org, kvmarm@lists•linux.dev,
linuxppc-dev@lists•ozlabs.org,
Isaku Yamahata <isaku.yamahata@gmail•com>
Subject: Re: [PATCH v7 5/8] KVM: x86/mmu: Don't pass FOLL_GET to __kvm_follow_pfn
Date: Mon, 10 Jul 2023 09:34:48 -0700 [thread overview]
Message-ID: <20230710163448.GE3894444@ls.amr.corp.intel.com> (raw)
In-Reply-To: <CAD=HUj6GiK3TSSe7UY8C2Jd+3tjZNBa-TLgk-UodyL=E+qKavg@mail.gmail.com>
On Fri, Jul 07, 2023 at 10:35:02AM +0900,
David Stevens <stevensd@chromium•org> wrote:
> > > > > diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
> > > > > index e44ab512c3a1..b1607e314497 100644
> > > > > --- a/arch/x86/kvm/mmu/mmu.c
> > > > > +++ b/arch/x86/kvm/mmu/mmu.c
> > > >
> > > > ...
> > > >
> > > > > @@ -2937,6 +2943,7 @@ static int mmu_set_spte(struct kvm_vcpu *vcpu, struct kvm_memory_slot *slot,
> > > > > bool host_writable = !fault || fault->map_writable;
> > > > > bool prefetch = !fault || fault->prefetch;
> > > > > bool write_fault = fault && fault->write;
> > > > > + bool is_refcounted = !fault || fault->is_refcounted_page;
> > > >
> > > > Just wonder, what if a non-refcounted page is prefetched? Or is it possible in
> > > > practice?
> > >
> > > Prefetching is still done via gfn_to_page_many_atomic, which sets
> > > FOLL_GET. That's fixable, but it's not something this series currently
> > > does.
> >
> > So if we prefetch a page, REFCOUNTED bit is cleared unconditionally with this
> > hunk. kvm_set_page_{dirty, accessed} won't be called as expected for prefetched
> > spte. If I read the patch correctly, REFCOUNTED bit in SPTE should represent
> > whether the corresponding page is ref-countable or not, right?
> >
> > Because direct_pte_prefetch_many() is for legacy KVM MMU and FNAME(prefetch_pte)
> > is shadow paging, we need to test it with legacy KVM MMU or shadow paging to hit
> > the issue, though.
> >
>
> direct_pte_prefetch_many and prefetch_gpte both pass NULL for the
> fault parameter, so is_refcounted will evaluate to true. So the spte's
> refcounted bit will get set in that case.
Oops, my bad. My point is "unconditionally". Is the bit always set for
non-refcountable pages? Or non-refcountable pages are not prefeched?
--
Isaku Yamahata <isaku.yamahata@gmail•com>
next prev parent reply other threads:[~2023-07-10 16:36 UTC|newest]
Thread overview: 55+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-07-04 7:50 [PATCH v7 0/8] KVM: allow mapping non-refcounted pages David Stevens
2023-07-04 7:50 ` [PATCH v7 1/8] KVM: Assert that a page's refcount is elevated when marking accessed/dirty David Stevens
2023-07-04 7:50 ` [PATCH v7 2/8] KVM: Introduce __kvm_follow_pfn function David Stevens
2023-07-05 3:10 ` Yu Zhang
2023-07-05 9:22 ` David Stevens
2023-07-05 10:53 ` Yu Zhang
2023-07-06 5:29 ` David Stevens
2023-07-06 14:52 ` Yu Zhang
2023-08-04 22:03 ` Sean Christopherson
2023-07-05 8:47 ` Zhi Wang
2023-07-05 9:08 ` David Stevens
2023-07-11 17:37 ` Zhi Wang
2023-07-06 1:34 ` Isaku Yamahata
2023-07-06 5:52 ` David Stevens
2023-08-04 22:13 ` Sean Christopherson
2023-07-04 7:50 ` [PATCH v7 3/8] KVM: Make __kvm_follow_pfn not imply FOLL_GET David Stevens
2023-07-05 7:23 ` Yu Zhang
2023-07-05 11:56 ` Yu Zhang
2023-07-06 6:09 ` David Stevens
2023-07-05 13:19 ` Zhi Wang
2023-07-06 6:49 ` David Stevens
2023-07-11 17:33 ` Zhi Wang
2023-07-11 21:59 ` Sean Christopherson
2023-09-05 8:26 ` David Stevens
2023-09-06 0:45 ` Sean Christopherson
2023-09-06 3:24 ` David Stevens
2023-09-06 22:03 ` Sean Christopherson
2023-07-04 7:50 ` [PATCH v7 4/8] KVM: x86/mmu: Migrate to __kvm_follow_pfn David Stevens
2023-07-05 8:07 ` Yu Zhang
2023-08-04 22:30 ` Sean Christopherson
2023-07-06 1:54 ` Isaku Yamahata
2023-08-24 8:03 ` David Stevens
2023-07-04 7:50 ` [PATCH v7 5/8] KVM: x86/mmu: Don't pass FOLL_GET " David Stevens
2023-07-05 10:18 ` Yu Zhang
2023-07-05 14:17 ` Yu Zhang
2023-07-06 4:52 ` David Stevens
2023-07-06 7:19 ` Yu Zhang
2023-07-06 15:58 ` Isaku Yamahata
2023-07-07 1:35 ` David Stevens
2023-07-10 16:34 ` Isaku Yamahata [this message]
2023-07-11 2:59 ` David Stevens
2023-08-04 22:45 ` Sean Christopherson
2023-07-05 10:25 ` Yu Zhang
2023-08-24 8:03 ` David Stevens
2023-08-24 15:15 ` Sean Christopherson
2023-08-25 1:38 ` David Stevens
2023-08-31 21:18 ` Sean Christopherson
2023-07-06 2:10 ` Isaku Yamahata
2023-07-06 5:18 ` David Stevens
2023-07-19 6:09 ` Yan Zhao
2023-07-19 7:16 ` David Stevens
2023-07-04 7:50 ` [PATCH v7 6/8] KVM: arm64: Migrate " David Stevens
2023-07-04 7:50 ` [PATCH v7 7/8] KVM: PPC: " David Stevens
2023-07-04 7:50 ` [PATCH v7 8/8] KVM: remove __gfn_to_pfn_memslot David Stevens
2023-08-04 22:47 ` [PATCH v7 0/8] KVM: allow mapping non-refcounted pages Sean Christopherson
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