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Subject: Re: [PATCH] KVM: x86: add hint to skip hidden rdpkru under
 kvm_load_host_xsave_state
To:     Paolo Bonzini <pbonzini@redhat.com>, Jon Kohler <jon@nutanix.com>
Cc:     Babu Moger <babu.moger@amd.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
        x86@kernel.org, "H. Peter Anvin" <hpa@zytor.com>,
        Sean Christopherson <seanjc@google.com>,
        Vitaly Kuznetsov <vkuznets@redhat.com>,
        Wanpeng Li <wanpengli@tencent.com>,
        Jim Mattson <jmattson@google.com>,
        Joerg Roedel <joro@8bytes.org>,
        Fenghua Yu <fenghua.yu@intel.com>,
        Yu-cheng Yu <yu-cheng.yu@intel.com>,
        Tony Luck <tony.luck@intel.com>,
        Uros Bizjak <ubizjak@gmail.com>,
        Petteri Aimonen <jpa@git.mail.kapsi.fi>,
        Kan Liang <kan.liang@linux.intel.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Mike Rapoport <rppt@kernel.org>,
        Benjamin Thiel <b.thiel@posteo.de>,
        Fan Yang <Fan_Yang@sjtu.edu.cn>,
        Juergen Gross <jgross@suse.com>,
        Dave Jiang <dave.jiang@intel.com>,
        "Peter Zijlstra (Intel)" <peterz@infradead.org>,
        Ricardo Neri <ricardo.neri-calderon@linux.intel.com>,
        Arvind Sankar <nivedita@alum.mit.edu>,
        linux-kernel@vger.kernel.org, kvm@vger.kernel.org
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 <16af038e-5b30-2509-4e3b-3b3ed9d4b81e@redhat.com>
From:   Dave Hansen <dave.hansen@intel.com>
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Message-ID: <709442d7-68e8-32a8-05b4-8a16748d9f11@intel.com>
Date:   Fri, 7 May 2021 09:58:38 -0700
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Precedence: bulk

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.