From: Ben Gardon <bgardon@google.com>
To: Paolo Bonzini <pbonzini@redhat.com>
Cc: LKML <linux-kernel@vger.kernel.org>, kvm <kvm@vger.kernel.org>,
Peter Xu <peterx@redhat.com>,
Sean Christopherson <seanjc@google.com>,
Peter Shier <pshier@google.com>,
Peter Feiner <pfeiner@google.com>,
Junaid Shahid <junaids@google.com>,
Jim Mattson <jmattson@google.com>,
Yulei Zhang <yulei.kernel@gmail.com>,
Wanpeng Li <kernellwp@gmail.com>,
Vitaly Kuznetsov <vkuznets@redhat.com>,
Xiao Guangrong <xiaoguangrong.eric@gmail.com>
Subject: Re: [PATCH 12/13] KVM: x86/mmu: Fast invalidation for TDP MMU
Date: Thu, 1 Apr 2021 09:50:05 -0700 [thread overview]
Message-ID: <CANgfPd_wFMFQgqSG9gi5zo3=WMGVST-66DkNJTopvTBZoangmQ@mail.gmail.com> (raw)
In-Reply-To: <79548215-b86f-99de-9322-c76ba5a1802d@redhat.com>
On Thu, Apr 1, 2021 at 3:36 AM Paolo Bonzini <pbonzini@redhat.com> wrote:
>
> On 31/03/21 23:08, Ben Gardon wrote:
> >
> > + if (is_tdp_mmu_enabled(kvm))
> > + kvm_tdp_mmu_invalidate_roots(kvm);
> > +
> > /*
> > * Toggle mmu_valid_gen between '0' and '1'. Because slots_lock is
> > * held for the entire duration of zapping obsolete pages, it's
> > @@ -5451,9 +5454,6 @@ static void kvm_mmu_zap_all_fast(struct kvm *kvm)
> >
> > kvm_zap_obsolete_pages(kvm);
> >
> > - if (is_tdp_mmu_enabled(kvm))
> > - kvm_tdp_mmu_zap_all(kvm);
> > -
>
> This is just cosmetic, but I'd prefer to keep the call to
> kvm_tdp_mmu_invalidate_roots at the original place, so that it's clear
> in the next patch that it's two separate parts because of the different
> locking requirements.
I'm not sure exactly what you mean and I could certainly do a better
job explaining in the commit description, but it's actually quite
important that kvm_tdp_mmu_invalidate_roots at least precede
kvm_zap_obsolete_pages as kvm_zap_obsolete_pages drops the lock and
yields. If kvm_tdp_mmu_invalidate_roots doesn't go first then vCPUs
could wind up dropping their ref on an old root and then picking it up
again before the last root had a chance to drop its ref.
Explaining in the description that kvm_tdp_mmu_zap_all is being
dropped because it is no longer necessary (as opposed to being moved)
might help make that cleaner.
Alternatively I could just leave kvm_tdp_mmu_zap_all and replace it in
the next patch.
>
> Paolo
>
next prev parent reply other threads:[~2021-04-01 18:33 UTC|newest]
Thread overview: 32+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-03-31 21:08 [PATCH 00/13] More parallel operations for the TDP MMU Ben Gardon
2021-03-31 21:08 ` [PATCH 01/13] KVM: x86/mmu: Re-add const qualifier in kvm_tdp_mmu_zap_collapsible_sptes Ben Gardon
2021-03-31 21:08 ` [PATCH 02/13] KVM: x86/mmu: Move kvm_mmu_(get|put)_root to TDP MMU Ben Gardon
2021-03-31 21:08 ` [PATCH 03/13] KVM: x86/mmu: use tdp_mmu_free_sp to free roots Ben Gardon
2021-03-31 21:08 ` [PATCH 04/13] KVM: x86/mmu: Merge TDP MMU put and free root Ben Gardon
2021-03-31 21:08 ` [PATCH 05/13] KVM: x86/mmu: comment for_each_tdp_mmu_root requires MMU write lock Ben Gardon
2021-03-31 21:08 ` [PATCH 06/13] KVM: x86/mmu: Refactor yield safe root iterator Ben Gardon
2021-03-31 21:08 ` [PATCH 07/13] KVM: x86/mmu: Make TDP MMU root refcount atomic Ben Gardon
2021-03-31 22:21 ` Sean Christopherson
2021-04-01 16:50 ` Ben Gardon
2021-03-31 21:08 ` [PATCH 08/13] KVM: x86/mmu: Protect the tdp_mmu_roots list with RCU Ben Gardon
2021-04-01 9:37 ` Paolo Bonzini
2021-04-01 16:48 ` Ben Gardon
2021-04-01 13:16 ` kernel test robot
2021-04-01 16:50 ` Ben Gardon
2021-03-31 21:08 ` [PATCH 09/13] KVM: x86/mmu: Allow zap gfn range to operate under the mmu read lock Ben Gardon
2021-04-01 9:58 ` Paolo Bonzini
2021-04-01 16:50 ` Ben Gardon
2021-03-31 21:08 ` [PATCH 10/13] KVM: x86/mmu: Allow zapping collapsible SPTEs to use MMU " Ben Gardon
2021-04-01 10:12 ` Paolo Bonzini
2021-03-31 21:08 ` [PATCH 11/13] KVM: x86/mmu: Allow enabling / disabling dirty logging under " Ben Gardon
2021-03-31 21:08 ` [PATCH 12/13] KVM: x86/mmu: Fast invalidation for TDP MMU Ben Gardon
2021-03-31 22:27 ` Sean Christopherson
2021-04-01 16:50 ` Ben Gardon
2021-04-01 10:36 ` Paolo Bonzini
2021-04-01 16:50 ` Ben Gardon [this message]
2021-04-01 17:02 ` Paolo Bonzini
2021-03-31 21:08 ` [PATCH 13/13] KVM: x86/mmu: Tear down roots in fast invalidation thread Ben Gardon
2021-03-31 22:29 ` Sean Christopherson
2021-04-01 10:41 ` Paolo Bonzini
2021-04-01 10:37 ` Paolo Bonzini
2021-04-01 10:43 ` [PATCH 00/13] More parallel operations for the TDP MMU Paolo Bonzini
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