linux-kernel - Re: [PATCH] KVM: x86: add hint to skip hidden rdpkru under kvm_load_host_xsave

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Date:   Fri, 7 May 2021 09:58:38 -0700
From:   Dave Hansen <dave.hansen@...el.com>
To:     Paolo Bonzini <pbonzini@...hat.com>, Jon Kohler <jon@...anix.com>
Cc:     Babu Moger <babu.moger@....com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        x86@...nel.org, "H. Peter Anvin" <hpa@...or.com>,
        Sean Christopherson <seanjc@...gle.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>,
        Fenghua Yu <fenghua.yu@...el.com>,
        Yu-cheng Yu <yu-cheng.yu@...el.com>,
        Tony Luck <tony.luck@...el.com>,
        Uros Bizjak <ubizjak@...il.com>,
        Petteri Aimonen <jpa@....mail.kapsi.fi>,
        Kan Liang <kan.liang@...ux.intel.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Mike Rapoport <rppt@...nel.org>,
        Benjamin Thiel <b.thiel@...teo.de>,
        Fan Yang <Fan_Yang@...u.edu.cn>,
        Juergen Gross <jgross@...e.com>,
        Dave Jiang <dave.jiang@...el.com>,
        "Peter Zijlstra (Intel)" <peterz@...radead.org>,
        Ricardo Neri <ricardo.neri-calderon@...ux.intel.com>,
        Arvind Sankar <nivedita@...m.mit.edu>,
        linux-kernel@...r.kernel.org, kvm@...r.kernel.org
Subject: Re: [PATCH] KVM: x86: add hint to skip hidden rdpkru under
 kvm_load_host_xsave_state

On 5/7/21 9:52 AM, Paolo Bonzini wrote:
> This can be optimized as well, can't it?  This means that the only case
> that needs the rdpkru is in switch_fpu_finish, and __write_pkru can be
> removed completely:
> 
> - do the rdpkru+wrpkru in switch_fpu_finish
> 
> - just use wrpkru in KVM

I was going to suggest exactly the same thing.  It doesn't require the
compiler to be smart, and wrpkru() is available in the same header as
__write_pkru().

I also detest the mysterious true/false arguments to functions where you
have no clue what they're doing at the call site without comments.