From: Lai Jiangshan <jiangshanlai@gmail.com>
To: Sean Christopherson <seanjc@google.com>
Cc: LKML <linux-kernel@vger.kernel.org>,
"open list:KERNEL VIRTUAL MACHINE FOR MIPS (KVM/mips)"
<kvm@vger.kernel.org>, Paolo Bonzini <pbonzini@redhat.com>,
Vitaly Kuznetsov <vkuznets@redhat.com>,
Maxim Levitsky <mlevitsk@redhat.com>,
Lai Jiangshan <jiangshan.ljs@antgroup.com>
Subject: Re: [PATCH 05/12] KVM: X86/MMU: Clear unsync bit directly in __mmu_unsync_walk()
Date: Thu, 21 Jul 2022 17:32:53 +0800 [thread overview]
Message-ID: <CAJhGHyAoM+6cOh7XQUvavgJcUts53FW6BnjM_wqMD6fkoYoB3w@mail.gmail.com> (raw)
In-Reply-To: <YtcLiNskPb8z/2Qc@google.com>
On Wed, Jul 20, 2022 at 3:52 AM Sean Christopherson <seanjc@google.com> wrote:
> > ---
> > arch/x86/kvm/mmu/mmu.c | 22 +++++++++++++---------
> > 1 file changed, 13 insertions(+), 9 deletions(-)
> >
> > diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
> > index f35fd5c59c38..2446ede0b7b9 100644
> > --- a/arch/x86/kvm/mmu/mmu.c
> > +++ b/arch/x86/kvm/mmu/mmu.c
> > @@ -1794,19 +1794,23 @@ static int __mmu_unsync_walk(struct kvm_mmu_page *sp,
> > return -ENOSPC;
> >
> > ret = __mmu_unsync_walk(child, pvec);
> > - if (!ret) {
> > - clear_unsync_child_bit(sp, i);
> > - continue;
> > - } else if (ret > 0) {
> > - nr_unsync_leaf += ret;
> > - } else
> > + if (ret < 0)
> > return ret;
> > - } else if (child->unsync) {
> > + nr_unsync_leaf += ret;
> > + }
> > +
> > + /*
> > + * Clear unsync bit for @child directly if @child is fully
> > + * walked and all the unsync shadow pages descended from
> > + * @child (including itself) are added into @pvec, the caller
> > + * must sync or zap all the unsync shadow pages in @pvec.
> > + */
> > + clear_unsync_child_bit(sp, i);
> > + if (child->unsync) {
> > nr_unsync_leaf++;
> > if (mmu_pages_add(pvec, child, i))
>
> This ordering is wrong, no? If the child itself is unsync and can't be added to
> @pvec, i.e. fails here, then clearing its bit in unsync_child_bitmap is wrong.
mmu_pages_add() can always successfully add the page to @pvec and
the caller needs to guarantee there is enough room to do so.
When it returns true, it means it will fail if you keep adding pages.
>
> I also dislike that that this patch obfuscates that a shadow page can't be unsync
> itself _and_ have unsync children (because only PG_LEVEL_4K can be unsync). In
> other words, keep the
>
> if (child->unsync_children) {
>
> } else if (child->unsync) {
>
> }
>
The code was not streamlined like this just because
I need to add some comments on clear_unsync_child_bit().
Duplicated clear_unsync_child_bit() would require
duplicated comments. I will use "See above" instead.
next prev parent reply other threads:[~2022-07-21 9:33 UTC|newest]
Thread overview: 27+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-06-05 6:43 [PATCH 00/12] KVM: X86/MMU: Simpliy mmu_unsync_walk() Lai Jiangshan
2022-06-05 6:43 ` [PATCH 01/12] KVM: X86/MMU: Warn if sp->unsync_children > 0 in link_shadow_page() Lai Jiangshan
2022-06-05 6:43 ` [PATCH 02/12] KVM: X86/MMU: Rename kvm_unlink_unsync_page() to kvm_mmu_page_clear_unsync() Lai Jiangshan
2022-07-14 22:10 ` Sean Christopherson
2022-06-05 6:43 ` [PATCH 03/12] KVM: X86/MMU: Split a part of kvm_unsync_page() as kvm_mmu_page_mark_unsync() Lai Jiangshan
2022-07-14 22:19 ` Sean Christopherson
2022-06-05 6:43 ` [PATCH 04/12] KVM: X86/MMU: Remove mmu_pages_clear_parents() Lai Jiangshan
2022-07-14 23:15 ` Sean Christopherson
2022-06-05 6:43 ` [PATCH 05/12] KVM: X86/MMU: Clear unsync bit directly in __mmu_unsync_walk() Lai Jiangshan
2022-07-19 19:52 ` Sean Christopherson
2022-07-21 9:32 ` Lai Jiangshan [this message]
2022-07-21 16:26 ` Sean Christopherson
2022-06-05 6:43 ` [PATCH 06/12] KVM: X86/MMU: Rename mmu_unsync_walk() to mmu_unsync_walk_and_clear() Lai Jiangshan
2022-07-19 20:07 ` Sean Christopherson
2022-06-05 6:43 ` [PATCH 07/12] KVM: X86/MMU: Remove the useless struct mmu_page_path Lai Jiangshan
2022-07-19 20:15 ` Sean Christopherson
2022-07-21 9:43 ` Lai Jiangshan
2022-07-21 15:25 ` Sean Christopherson
2022-06-05 6:43 ` [PATCH 08/12] KVM: X86/MMU: Remove the useless idx from struct kvm_mmu_pages Lai Jiangshan
2022-07-19 20:31 ` Sean Christopherson
2022-06-05 6:43 ` [PATCH 09/12] KVM: X86/MMU: Unfold struct mmu_page_and_offset in " Lai Jiangshan
2022-06-05 6:43 ` [PATCH 10/12] KVM: X86/MMU: Don't add parents to " Lai Jiangshan
2022-07-19 20:34 ` Sean Christopherson
2022-06-05 6:43 ` [PATCH 11/12] KVM: X86/MMU: Remove mmu_pages_first() and mmu_pages_next() Lai Jiangshan
2022-07-19 20:40 ` Sean Christopherson
2022-06-05 6:43 ` [PATCH 12/12] KVM: X86/MMU: Rename struct kvm_mmu_pages to struct kvm_mmu_page_vec Lai Jiangshan
2022-07-19 20:45 ` Sean Christopherson
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