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Date:   Mon, 28 Mar 2022 14:51:21 +0000
From:   Sean Christopherson <seanjc@google.com>
To:     Jon Kohler <jon@nutanix.com>
Cc:     Paolo Bonzini <pbonzini@redhat.com>,
        Vitaly Kuznetsov <vkuznets@redhat.com>,
        Wanpeng Li <wanpengli@tencent.com>,
        Jim Mattson <jmattson@google.com>,
        Joerg Roedel <joro@8bytes.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
        Dave Hansen <dave.hansen@linux.intel.com>,
        "x86@kernel.org" <x86@kernel.org>,
        "H. Peter Anvin" <hpa@zytor.com>,
        "kvm@vger.kernel.org" <kvm@vger.kernel.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH] KVM: x86: optimize PKU branching in
 kvm_load_{guest|host}_xsave_state
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References: <20220324004439.6709-1-jon@nutanix.com>
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On Mon, Mar 28, 2022, Jon Kohler wrote:
> 
> 
> > On Mar 27, 2022, at 6:43 AM, Paolo Bonzini <pbonzini@redhat.com> wrote:
> > 
> > On 3/26/22 02:37, Jon Kohler wrote:
> >>>>    Flip the ordering of the || condition so that XFEATURE_MASK_PKRU is
> >>>>    checked first, which when instrumented in our environment appeared
> >>>>    to be always true and less overall work than kvm_read_cr4_bits.
> >>> 
> >>> If it's always true, then it should be checked last, not first.  And if
> >> Sean thanks for the review. This would be a left handed || short circuit, so
> >> wouldn’t we want always true to be first?
> > 
> > Yes.
> 
> Ack, thanks.

Yeah, I lost track of whether it was a || or &&.