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From: Sean Christopherson <seanjc@google.com>
To: Paolo Bonzini <pbonzini@redhat.com>
Cc: Vitaly Kuznetsov <vkuznets@redhat.com>,
	Wanpeng Li <wanpengli@tencent.com>,
	Jim Mattson <jmattson@google.com>, Joerg Roedel <joro@8bytes.org>,
	kvm@vger.kernel.org, linux-kernel@vger.kernel.org,
	Ben Gardon <bgardon@google.com>
Subject: Re: [PATCH 1/2] KVM: x86/mmu: Don't skip non-leaf SPTEs when zapping all SPTEs
Date: Thu, 12 Aug 2021 18:09:59 +0000	[thread overview]
Message-ID: <YRVj94P6it0ow8J+@google.com> (raw)
In-Reply-To: <YRVPxCv2RtyXi+XO@google.com>

On Thu, Aug 12, 2021, Sean Christopherson wrote:
> On Thu, Aug 12, 2021, Paolo Bonzini wrote:
> > On 12/08/21 07:07, Sean Christopherson wrote:
> > > @@ -739,8 +749,16 @@ static bool zap_gfn_range(struct kvm *kvm, struct kvm_mmu_page *root,
> > >   			  gfn_t start, gfn_t end, bool can_yield, bool flush,
> > >   			  bool shared)
> > >   {
> > > +	bool zap_all = (end == ZAP_ALL_END);
> > >   	struct tdp_iter iter;
> > > +	/*
> > > +	 * Bound the walk at host.MAXPHYADDR, guest accesses beyond that will
> > > +	 * hit a #PF(RSVD) and never get to an EPT Violation/Misconfig / #NPF,
> > > +	 * and so KVM will never install a SPTE for such addresses.
> > > +	 */
> > > +	end = min(end, 1ULL << (shadow_phys_bits - PAGE_SHIFT));
> > 
> > Then zap_all need not have any magic value.  You can use 0/-1ull, it's
> > readable enough.  ZAP_ALL_END is also unnecessary here if you do:
> > 
> > 	gfn_t max_gfn_host = 1ULL << (shadow_phys_bits - PAGE_SHIFT);
> > 	bool zap_all = (start == 0 && end >= max_gfn_host);
> 
> Aha!  Nice.  I was both too clever and yet not clever enough.

And as a bonus, this also works for kvm_post_set_cr0(), which calls the common
kvm_zap_gfn_range() with 0 - ALL_ONES.

  reply	other threads:[~2021-08-12 18:10 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 [this message]
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
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

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