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From: Sean Christopherson <seanjc@google.com>
To: Mathias Krause <minipli@grsecurity.net>
Cc: kvm@vger.kernel.org, linux-kernel@vger.kernel.org,
	Paolo Bonzini <pbonzini@redhat.com>
Subject: Re: [PATCH v3 4/6] KVM: x86: Make use of kvm_read_cr*_bits() when testing bits
Date: Tue, 21 Mar 2023 08:57:37 -0700	[thread overview]
Message-ID: <ZBnT8XhO9WuQFFK0@google.com> (raw)
In-Reply-To: <7b428c85-5f20-a077-70b6-f361d2e7ffe7@grsecurity.net>

On Mon, Mar 20, 2023, Mathias Krause wrote:
> On 15.03.23 23:18, Sean Christopherson wrote:
> > On Wed, Feb 01, 2023, Mathias Krause wrote:
> >> Make use of the kvm_read_cr{0,4}_bits() helper functions when we only
> >> want to know the state of certain bits instead of the whole register.
> >>
> >> This not only makes the intend cleaner, it also avoids a VMREAD in case
> >> the tested bits aren't guest owned.
> >>
> >> Signed-off-by: Mathias Krause <minipli@grsecurity.net>
> >> ---
> >>  arch/x86/kvm/pmu.c     | 4 ++--
> >>  arch/x86/kvm/vmx/vmx.c | 4 ++--
> >>  2 files changed, 4 insertions(+), 4 deletions(-)
> >>
> >> diff --git a/arch/x86/kvm/pmu.c b/arch/x86/kvm/pmu.c
> >> index d939d3b84e6f..d9922277df67 100644
> >> --- a/arch/x86/kvm/pmu.c
> >> +++ b/arch/x86/kvm/pmu.c
> >> @@ -439,9 +439,9 @@ int kvm_pmu_rdpmc(struct kvm_vcpu *vcpu, unsigned idx, u64 *data)
> >>  	if (!pmc)
> >>  		return 1;
> >>  
> >> -	if (!(kvm_read_cr4(vcpu) & X86_CR4_PCE) &&
> >> +	if (!(kvm_read_cr4_bits(vcpu, X86_CR4_PCE)) &&
> > 
> > Purely as an FYI, I proposed adding helpers to query single CR0/CR4 bits in a
> > separate thread[*].  No need to do anything on your end, I'll plan on applying
> > this patch first and will handle whatever conflicts arise.
> > 
> > [*] https://lore.kernel.org/all/ZAuRec2NkC3+4jvD@google.com
> 
> Unfortunately, not all users of kvm_read_cr*_bits() only want to read a
> single bit. There are a very few that read bit masks -- but you're
> probably fully aware of this.

Yeah, we won't be able to get rid of kvm_read_cr*_bits() entirely, the goal is
purely to make code that does query a single bit slightly more readable/obvious.

  reply	other threads:[~2023-03-21 15:57 UTC|newest]

Thread overview: 24+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2023-02-01 19:45 [PATCH v3 0/6] KVM: MMU: performance tweaks for heavy CR0.WP users Mathias Krause
2023-02-01 19:45 ` [PATCH v3 1/6] KVM: x86/mmu: Avoid indirect call for get_cr3 Mathias Krause
2023-02-01 19:46 ` [PATCH v3 2/6] KVM: VMX: Avoid retpoline call for control register caused exits Mathias Krause
2023-03-15 21:38   ` Sean Christopherson
2023-03-20 20:43     ` Mathias Krause
2023-02-01 19:46 ` [PATCH v3 3/6] KVM: x86: Do not unload MMU roots when only toggling CR0.WP Mathias Krause
2023-02-07 13:36   ` Zhi Wang
2023-02-08  9:52     ` Mathias Krause
2023-03-15 21:22       ` Sean Christopherson
2023-03-15 22:11   ` Sean Christopherson
2023-03-20 21:13     ` Mathias Krause
2023-02-01 19:46 ` [PATCH v3 4/6] KVM: x86: Make use of kvm_read_cr*_bits() when testing bits Mathias Krause
2023-02-07 13:05   ` Zhi Wang
2023-02-08  9:11     ` Mathias Krause
2023-02-14 11:08       ` Zhi Wang
2023-03-15 22:18   ` Sean Christopherson
2023-03-20 21:34     ` Mathias Krause
2023-03-21 15:57       ` Sean Christopherson [this message]
2023-02-01 19:46 ` [PATCH v3 5/6] KVM: x86/mmu: Fix comment typo Mathias Krause
2023-02-01 19:46 ` [PATCH v3 6/6] KVM: VMX: Make CR0.WP a guest owned bit Mathias Krause
2023-03-15 22:30   ` Sean Christopherson
2023-03-20 21:31     ` Mathias Krause
2023-03-06  6:34 ` [PATCH v3 0/6] KVM: MMU: performance tweaks for heavy CR0.WP users Mathias Krause
2023-03-06 18:07   ` Sean Christopherson

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