linux-kernel - Re: [PATCH 11/11] KVM/MMU: Flush tlb in the kvm_age

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Date:   Mon, 7 Jan 2019 11:42:59 +0800
From:   Tianyu Lan <lantianyu1986@...il.com>
To:     Sean Christopherson <sean.j.christopherson@...el.com>
Cc:     Lan Tianyu <Tianyu.Lan@...rosoft.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Radim Krcmar <rkrcmar@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, bp@...en8.de,
        "H. Peter Anvin" <hpa@...or.com>,
        "the arch/x86 maintainers" <x86@...nel.org>,
        kvm <kvm@...r.kernel.org>,
        "linux-kernel@...r kernel org" <linux-kernel@...r.kernel.org>,
        michael.h.kelley@...rosoft.com, kys@...rosoft.com,
        vkuznets@...hat.com, linux@...linux.org.uk
Subject: Re: [PATCH 11/11] KVM/MMU: Flush tlb in the kvm_age_rmapp()

Hi Sean:
             Thanks for your review.

On Sat, Jan 5, 2019 at 12:12 AM Sean Christopherson
<sean.j.christopherson@...el.com> wrote:
>
> On Fri, Jan 04, 2019 at 04:54:05PM +0800, lantianyu1986@...il.com wrote:
> > From: Lan Tianyu <Tianyu.Lan@...rosoft.com>
> >
> > This patch is to flush tlb in the kvm_age_rmapp() when tlb range flush
> > is available and flush request is true.
> >
> > Signed-off-by: Lan Tianyu <Tianyu.Lan@...rosoft.com>
> > ---
> >  arch/x86/kvm/mmu.c | 7 +++++++
> >  1 file changed, 7 insertions(+)
> >
> > diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c
> > index a5728f51bf7d..bc402a72956a 100644
> > --- a/arch/x86/kvm/mmu.c
> > +++ b/arch/x86/kvm/mmu.c
> > @@ -1958,10 +1958,17 @@ static int kvm_age_rmapp(struct kvm *kvm, struct kvm_rmap_head *rmap_head,
> >       u64 *sptep;
> >       struct rmap_iterator uninitialized_var(iter);
> >       int young = 0;
> > +     bool flush = (bool)data;
> >
> >       for_each_rmap_spte(rmap_head, &iter, sptep)
> >               young |= mmu_spte_age(sptep);
> >
> > +     if (young && flush) {
> > +             kvm_flush_remote_tlbs_with_address(kvm, gfn,
> > +                             KVM_PAGES_PER_HPAGE(level));
> > +             young = 0;
> > +     }
> > +
>
> young shouldn't be cleared, the tracing will be wrong and the caller
> might actually care about the return value.

Yes, this is wrong and will update.

> I'm assuming you're
> clearing young to avoid the flush in kvm_mmu_notifier_clear_flush_young(),
> but keeping that flush is silly since it will never be invoked.  Just
> squash this patch with patch 10/11 so that you can remove the unnecessary
> flush in kvm_mmu_notifier_clear_flush_young() and preserve young.
>

The platform may provide tlb flush with address range as granularity. My changes
are to use range flush when it's available. kvm_mmu_notifier_clear_flush_young()
is common function for all platforms and most platforms still need the
flush in the
kvm_mmu_notifier_clear_flush_young(). I think it's better to separate
flush request and
"young" from return value of kvm_age_hva(). New flush parameter I
added in the patch 10
can be changed to a pointer and kvm_age_hva() can use it to return
flush request.

-- 
Best regards
Tianyu Lan