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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>,
	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 6/6] KVM: x86/mmu: Lazily allocate memslot rmaps
Date: Wed, 28 Apr 2021 09:45:56 -0700	[thread overview]
Message-ID: <CANgfPd_o+UA4ry7Kpw3WbcPZYm32r+1o=hQmZdazsrZvO4aynA@mail.gmail.com> (raw)
In-Reply-To: <1b598516-4478-4de2-4241-d4b517ec03fa@redhat.com>

On Wed, Apr 28, 2021 at 3:04 AM Paolo Bonzini <pbonzini@redhat.com> wrote:
>
> On 28/04/21 00:36, Ben Gardon wrote:
> > -static int kvm_alloc_memslot_metadata(struct kvm_memory_slot *slot,
> > +static int kvm_alloc_memslot_metadata(struct kvm *kvm,
> > +                                   struct kvm_memory_slot *slot,
> >                                     unsigned long npages)
> >   {
> >       int i;
> > @@ -10892,7 +10950,7 @@ static int kvm_alloc_memslot_metadata(struct kvm_memory_slot *slot,
> >        */
> >       memset(&slot->arch, 0, sizeof(slot->arch));
> >
> > -     r = alloc_memslot_rmap(slot, npages);
> > +     r = alloc_memslot_rmap(kvm, slot, npages);
> >       if (r)
> >               return r;
> >
>
> I wonder why you need alloc_memslot_rmap at all here in
> kvm_alloc_memslot_metadata, or alternatively why you need to do it in
> kvm_arch_assign_memslots.  It seems like only one of those would be
> necessary.

Oh, that's a good point. We need it in kvm_arch_assign_memslots
because of the race I identified in the thread for patch 5 of this
series, but we could remove it from kvm_alloc_memslot_metadata with
this patch.

Of course, it would be much nicer if we could just keep it in
kvm_alloc_memslot_metadata and find some other way to stop memslots
without rmaps from being inappropriately installed, if anyone has a
simpler way to accomplish that.

>
> Paolo
>

      reply	other threads:[~2021-04-28 16:46 UTC|newest]

Thread overview: 22+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-04-27 22:36 [PATCH 0/6] Lazily allocate memslot rmaps Ben Gardon
2021-04-27 22:36 ` [PATCH 1/6] KVM: x86/mmu: Track if shadow MMU active Ben Gardon
2021-04-27 22:36 ` [PATCH 2/6] KVM: x86/mmu: Skip rmap operations if shadow MMU inactive Ben Gardon
2021-04-27 22:36 ` [PATCH 3/6] KVM: x86/mmu: Deduplicate rmap freeing in allocate_memslot_rmap Ben Gardon
2021-04-28 10:00   ` Paolo Bonzini
2021-04-28 16:23     ` Ben Gardon
2021-04-27 22:36 ` [PATCH 4/6] KVM: x86/mmu: Factor out allocating memslot rmap Ben Gardon
2021-04-27 22:36 ` [PATCH 5/6] KVM: x86/mmu: Protect kvm->memslots with a mutex Ben Gardon
2021-04-28  6:25   ` Paolo Bonzini
2021-04-28 16:40     ` Ben Gardon
2021-04-28 17:46       ` Paolo Bonzini
2021-04-28 20:40         ` Ben Gardon
2021-04-28 21:41           ` Paolo Bonzini
2021-04-28 21:46             ` Ben Gardon
2021-04-28 23:42               ` Paolo Bonzini
2021-04-29  0:40                 ` Sean Christopherson
2021-04-29  1:42                   ` Sean Christopherson
2021-04-29  7:02                   ` Paolo Bonzini
2021-04-29 17:45                     ` Ben Gardon
2021-04-27 22:36 ` [PATCH 6/6] KVM: x86/mmu: Lazily allocate memslot rmaps Ben Gardon
2021-04-28 10:03   ` Paolo Bonzini
2021-04-28 16:45     ` Ben Gardon [this message]

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