From: Sean Christopherson <seanjc@google.com>
To: Paolo Bonzini <pbonzini@redhat.com>
Cc: Ben Gardon <bgardon@google.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 17:33:30 +0000 [thread overview]
Message-ID: <YRVbamoQhvPmrEgK@google.com> (raw)
In-Reply-To: <928be04d-e60e-924c-1f3a-cb5fef8b0042@redhat.com>
On Thu, Aug 12, 2021, Paolo Bonzini wrote:
> On 12/08/21 19:07, Sean Christopherson wrote:
> > 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.
>
> I think it makes sense to have it. You can even use the ternary operator
Hah, yeah, I almost used a ternary op. Honestly don't know why I didn't, guess
my brain flipped a coin.
>
> /*
> * When zapping everything, all entries at the top level
> * ultimately go away, and the levels below go down with them.
> * So do not bother iterating all the way down to the leaves.
The subtle part is that try_step_down() won't actually iterate down because it
explicitly rereads and rechecks the SPTE.
if (iter->level == iter->min_level)
return false;
/*
* Reread the SPTE before stepping down to avoid traversing into page
* tables that are no longer linked from this entry.
*/
iter->old_spte = READ_ONCE(*rcu_dereference(iter->sptep)); \
---> this is the code that is avoided
child_pt = spte_to_child_pt(iter->old_spte, iter->level); /
if (!child_pt)
return false;
My comment wasn't all that accurate either. Maybe this?
/*
* No need to try to step down in the iterator when zapping all SPTEs,
* zapping the top-level non-leaf SPTEs will recurse on their children.
*/
int min_level = zap_all ? root->role.level : PG_LEVEL_4K;
> */
> int min_level = zap_all ? root->role.level : PG_LEVEL_4K;
>
> Paolo
>
next prev parent reply other threads:[~2021-08-12 17:33 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
2021-08-12 17:15 ` Paolo Bonzini
2021-08-12 17:33 ` Sean Christopherson [this message]
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=YRVbamoQhvPmrEgK@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 \
/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
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
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).