LKML Archive on lore.kernel.org
help / color / mirror / Atom feed
From: Sean Christopherson <seanjc@google.com>
To: Ben Gardon <bgardon@google.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>,
	Vitaly Kuznetsov <vkuznets@redhat.com>,
	Wanpeng Li <wanpengli@tencent.com>,
	Jim Mattson <jmattson@google.com>, Joerg Roedel <joro@8bytes.org>,
	kvm <kvm@vger.kernel.org>, LKML <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH 2/2] KVM: x86/mmu: Don't step down in the TDP iterator when zapping all SPTEs
Date: Thu, 12 Aug 2021 17:07:36 +0000	[thread overview]
Message-ID: <YRVVWC31fuZiw9tT@google.com> (raw)
In-Reply-To: <CANgfPd8HSYZbqmi21XQ=XeMCndXJ0+Ld0eZNKPWLa1fKtutiBA@mail.gmail.com>

On Thu, Aug 12, 2021, Ben Gardon wrote:
> On Wed, Aug 11, 2021 at 10:07 PM Sean Christopherson <seanjc@google.com> wrote:
> >
> > Set the min_level for the TDP iterator at the root level when zapping all
> > SPTEs so that the _iterator_ only processes top-level SPTEs.  Zapping a
> > non-leaf SPTE will recursively zap all its children, thus there is no
> > need for the iterator to attempt to step down.  This avoids rereading all
> > the top-level SPTEs after they are zapped by causing try_step_down() to
> > short-circuit.
> >
> > Cc: Ben Gardon <bgardon@google.com>
> > Signed-off-by: Sean Christopherson <seanjc@google.com>
> 
> This change looks functionally correct, but I'm not sure it's worth
> adding more code special cased on zap-all for what seems like a small
> performance improvement in a context which shouldn't be particularly
> performance sensitive.

Yeah, I was/am on the fence too, I almost included a blurb in the cover letter
saying as much.  I'll do that for v2 and let Paolo decide.

Thanks!

> Change is a correct optimization though and it's not much extra code,
> so I'm happy to give a:
> Reviewed-by: Ben Gardon <bgardon@google.com>

  reply	other threads:[~2021-08-12 17:07 UTC|newest]

Thread overview: 15+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-08-12  5:07 [PATCH 0/2] KVM: x86/mmu: Fix a TDP MMU leak and optimize zap all Sean Christopherson
2021-08-12  5:07 ` [PATCH 1/2] KVM: x86/mmu: Don't skip non-leaf SPTEs when zapping all SPTEs Sean Christopherson
2021-08-12 16:18   ` Paolo Bonzini
2021-08-12 16:43     ` Sean Christopherson
2021-08-12 18:09       ` Sean Christopherson
2021-08-12  5:07 ` [PATCH 2/2] KVM: x86/mmu: Don't step down in the TDP iterator " Sean Christopherson
2021-08-12 16:47   ` Ben Gardon
2021-08-12 17:07     ` Sean Christopherson [this message]
2021-08-12 17:15       ` Paolo Bonzini
2021-08-12 17:33         ` Sean Christopherson
2021-08-12 17:38           ` Paolo Bonzini
2021-08-12 17:46             ` Sean Christopherson
2021-08-13  7:27               ` Paolo Bonzini
2021-08-13 16:13                 ` Sean Christopherson
2021-08-13 16:38                   ` Paolo Bonzini

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=YRVVWC31fuZiw9tT@google.com \
    --to=seanjc@google.com \
    --cc=bgardon@google.com \
    --cc=jmattson@google.com \
    --cc=joro@8bytes.org \
    --cc=kvm@vger.kernel.org \
    --cc=linux-kernel@vger.kernel.org \
    --cc=pbonzini@redhat.com \
    --cc=vkuznets@redhat.com \
    --cc=wanpengli@tencent.com \
    --subject='Re: [PATCH 2/2] KVM: x86/mmu: Don'\''t step down in the TDP iterator when zapping all SPTEs' \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).