linux-kernel - Re: [PATCH v3] KVM: x86: use wrpkru directly in kvm_load_{guest|host}_xsave

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Date:   Tue, 11 May 2021 12:08:44 -0700
From:   Dave Hansen <dave.hansen@...el.com>
To:     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>,
        Paolo Bonzini <pbonzini@...hat.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>,
        Yu-cheng Yu <yu-cheng.yu@...el.com>,
        Fenghua Yu <fenghua.yu@...el.com>,
        Tony Luck <tony.luck@...el.com>,
        Uros Bizjak <ubizjak@...il.com>,
        Petteri Aimonen <jpa@....mail.kapsi.fi>,
        Al Viro <viro@...iv.linux.org.uk>,
        Kan Liang <kan.liang@...ux.intel.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Mike Rapoport <rppt@...nel.org>,
        Fan Yang <Fan_Yang@...u.edu.cn>,
        Juergen Gross <jgross@...e.com>,
        Benjamin Thiel <b.thiel@...teo.de>,
        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 v3] KVM: x86: use wrpkru directly in
 kvm_load_{guest|host}_xsave_state

On 5/11/21 10:05 AM, Jon Kohler wrote:
> To improve performance, use wrpkru directly in KVM code and simplify
> the uses of __write_pkru such that it can be removed completely.

I don't love the repeated:

+	if (pkru_val != rdpkru())
+		wrpkru(pkru_val);

But, all of the w*pkru() variants were getting confusing, even to me. :)

Being explicit about the "wkpkru suppression" in a limited number of
places looks fine.

Acked-by: Dave Hansen <dave.hansen@...el.com>