From: Sean Christopherson <seanjc@google.com>
To: Vipin Sharma <vipinsh@google.com>
Cc: Ben Gardon <bgardon@google.com>,
David Matlack <dmatlack@google.com>,
pbonzini@redhat.com, kvm@vger.kernel.org,
linux-kernel@vger.kernel.org
Subject: Re: [Patch] KVM: x86/mmu: Make optimized __handle_changed_spte() for clear dirty log
Date: Mon, 30 Jan 2023 18:09:32 +0000 [thread overview]
Message-ID: <Y9gH3OHA4ftegU7X@google.com> (raw)
In-Reply-To: <CAHVum0cd=YKvEKi7xZZHCTBn9XAxiax92JHV_W47R8rYvvnF-g@mail.gmail.com>
On Sat, Jan 28, 2023, Vipin Sharma wrote:
> On Wed, Jan 25, 2023 at 5:49 PM Sean Christopherson <seanjc@google.com> wrote:
> > -static void handle_changed_spte(struct kvm *kvm, int as_id, gfn_t gfn,
> > - u64 old_spte, u64 new_spte, int level,
> > - bool shared)
> > -{
> > - __handle_changed_spte(kvm, as_id, gfn, old_spte, new_spte, level,
> > - shared);
> > handle_changed_spte_acc_track(old_spte, new_spte, level);
> > - handle_changed_spte_dirty_log(kvm, as_id, gfn, old_spte,
> > - new_spte, level);
> > +
> > + /* COMMENT GOES HERE. */
>
> Current "shared" callers are not making a page dirty. If a new
> "shared" caller makes a page dirty then make sure
> handle_changed_spte_dirty_log is called.
>
> How is this?
I was hoping for a more definitive "rule" than "KVM doesn't currently do XYZ".
> > + if (!shared)
> > + handle_changed_spte_dirty_log(kvm, as_id, gfn, old_spte,
> > + new_spte, level);
> > }
> >
> > /*
> > * tdp_mmu_set_spte_atomic - Set a TDP MMU SPTE atomically
> > - * and handle the associated bookkeeping. Do not mark the page dirty
> > - * in KVM's dirty bitmaps.
> > + * and handle the associated bookkeeping.
> > *
> > * If setting the SPTE fails because it has changed, iter->old_spte will be
> > * refreshed to the current value of the spte.
...
> > @@ -1703,9 +1657,11 @@ static void clear_dirty_pt_masked(struct kvm *kvm, struct kvm_mmu_page *root,
> > new_spte = iter.old_spte & ~shadow_dirty_mask;
> > else
> > continue;
> > +
> > + kvm_set_pfn_dirty(spte_to_pfn(iter.old_spte));
> > }
> >
>
> Shouldn't we handle spte_ad_need_write_protect(iter.old_spte)
> separately and if this function returns true then on clearing
> PT_WRITABLE_MASK, kvm_set_pfn_dirty be called?
> My understanding is that the spte_ad_need_write_protect() will return
> true for nested VM sptes when PML mode is enabled.
Ah rats. I missed that is_dirty_spte() checks WRITABLE in that case. So yeah,
kvm_set_pfn_dirty() should be called in both paths. I was thinking KVM would mark
the page dirty when faulting the PFN for write, but I have my flows all mixed up.
next prev parent reply other threads:[~2023-01-30 18:09 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-01-25 21:38 [Patch] KVM: x86/mmu: Make optimized __handle_changed_spte() for clear dirty log Vipin Sharma
2023-01-25 22:00 ` David Matlack
2023-01-25 22:25 ` Ben Gardon
2023-01-26 0:40 ` Vipin Sharma
2023-01-26 1:49 ` Sean Christopherson
2023-01-28 17:20 ` Vipin Sharma
2023-01-30 18:09 ` Sean Christopherson [this message]
2023-01-30 20:17 ` Vipin Sharma
2023-01-30 22:49 ` Sean Christopherson
2023-01-30 22:12 ` David Matlack
2023-01-30 23:49 ` Sean Christopherson
2023-01-31 17:41 ` David Matlack
2023-01-31 18:01 ` Vipin Sharma
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