Re: [PATCH] KVM: x86: add hint to skip hidden rdpkru under kvm_load_host_xsave_state

From: Jon Kohler <jon@nutanix.com>
To: Dave Hansen <dave.hansen@intel.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>, Jon Kohler <jon@nutanix.com>,
	Babu Moger <babu.moger@amd.com>,
	Thomas Gleixner <tglx@linutronix.de>,
	Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
	"x86@kernel.org" <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" <linux-kernel@vger.kernel.org>,
	"kvm@vger.kernel.org" <kvm@vger.kernel.org>
Subject: Re: [PATCH] KVM: x86: add hint to skip hidden rdpkru under kvm_load_host_xsave_state
Date: Fri, 7 May 2021 17:13:36 +0000	[thread overview]
Message-ID: <4E9EC06E-4575-44AA-89BC-619439385521@nutanix.com> (raw)
In-Reply-To: <709442d7-68e8-32a8-05b4-8a16748d9f11@intel.com>

> On May 7, 2021, at 12:58 PM, Dave Hansen <dave.hansen@intel.com> wrote:
> 
> 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().

Thanks Paolo, Dave. Good suggestion, I’ll work up a v2 and send it out.

> 
> 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.

Noted, my apologies. Thats a good point, I won’t make that mistake again.