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Subject: Re: [PATCH v2] KVM: x86: use wrpkru directly in
 kvm_load_{guest|host}_xsave_state
To:     Dave Hansen <dave.hansen@intel.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>,
        Yu-cheng Yu <yu-cheng.yu@intel.com>,
        Fenghua Yu <fenghua.yu@intel.com>,
        Tony Luck <tony.luck@intel.com>,
        Petteri Aimonen <jpa@git.mail.kapsi.fi>,
        Kan Liang <kan.liang@linux.intel.com>,
        Uros Bizjak <ubizjak@gmail.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Mike Rapoport <rppt@kernel.org>,
        Benjamin Thiel <b.thiel@posteo.de>,
        Anshuman Khandual <anshuman.khandual@arm.com>,
        Juergen Gross <jgross@suse.com>,
        Fan Yang <Fan_Yang@sjtu.edu.cn>,
        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
References: <20210511155922.36693-1-jon@nutanix.com>
 <ab09f739-89fa-901d-9ee3-27a6c674d9a0@intel.com>
From:   Paolo Bonzini <pbonzini@redhat.com>
Message-ID: <95947b5c-9add-e5d3-16a5-a40ab6d24978@redhat.com>
Date:   Tue, 11 May 2021 19:08:06 +0200
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On 11/05/21 18:45, Dave Hansen wrote:
> On 5/11/21 8:59 AM, Jon Kohler wrote:
>> diff --git a/arch/x86/include/asm/pgtable.h b/arch/x86/include/asm/pgtable.h
>> index b1099f2d9800..20f1fb8be7ef 100644
>> --- a/arch/x86/include/asm/pgtable.h
>> +++ b/arch/x86/include/asm/pgtable.h
>> @@ -151,7 +151,7 @@ static inline void write_pkru(u32 pkru)
>>   	fpregs_lock();
>>   	if (pk)
>>   		pk->pkru = pkru;
>> -	__write_pkru(pkru);
>> +	wrpkru(pkru);
>>   	fpregs_unlock();
>>   }
> 
> This removes the:
> 
> 	if (pkru == rdpkru())
> 		return;
> 
> optimization from a couple of write_pkru() users:
> arch_set_user_pkey_access() and copy_init_pkru_to_fpregs().
> 
> Was that intentional?  Those aren't the hottest paths in the kernel, but
> copy_init_pkru_to_fpregs() is used in signal handling and exeve().

Yeah, you should move it from __write_pkru() to write_pkru() but not 
remove it completely.

Paolo