linux-kernel - Re: [PATCH v10 6/7] x86/arch_prctl: Add ARCH_[GET|SET]

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Message-ID: <1acdafa1-4557-b147-ef67-069886255e6c@zytor.com>
Date:   Tue, 14 Mar 2017 13:06:53 -0700
From:   "H. Peter Anvin" <hpa@...or.com>
To:     Kyle Huey <me@...ehuey.com>
Cc:     "Robert O'Callahan" <robert@...llahan.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Andy Lutomirski <luto@...nel.org>,
        Ingo Molnar <mingo@...hat.com>,
        "maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)" <x86@...nel.org>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Radim Krčmář <rkrcmar@...hat.com>,
        Jeff Dike <jdike@...toit.com>,
        Richard Weinberger <richard@....at>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        Shuah Khan <shuah@...nel.org>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Borislav Petkov <bp@...e.de>,
        Peter Zijlstra <peterz@...radead.org>,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        Len Brown <len.brown@...el.com>,
        "Rafael J. Wysocki" <rafael.j.wysocki@...el.com>,
        Dmitry Safonov <dsafonov@...tuozzo.com>,
        David Matlack <dmatlack@...gle.com>,
        open list <linux-kernel@...r.kernel.org>,
        "open list:USER-MODE LINUX (UML)" 
        <user-mode-linux-devel@...ts.sourceforge.net>,
        "open list:USER-MODE LINUX (UML)" 
        <user-mode-linux-user@...ts.sourceforge.net>,
        "open list:FILESYSTEMS (VFS and infrastructure)" 
        <linux-fsdevel@...r.kernel.org>,
        "open list:KERNEL SELFTEST FRAMEWORK" 
        <linux-kselftest@...r.kernel.org>, kvm list <kvm@...r.kernel.org>
Subject: Re: [PATCH v10 6/7] x86/arch_prctl: Add ARCH_[GET|SET]_CPUID

On 03/14/17 12:08, Kyle Huey wrote:
> 
> That's largely what we ended up doing.  See
> https://lkml.org/lkml/2017/2/14/80 and the latest version of this
> patch, https://lkml.org/lkml/2017/3/11/197.
> 

Yes, as I said, my mistake.

I would still like to see an early-out when none of these flags are set
(I just discussed this with tglx on IRC):

if (likely(!((tifp|tifn) &
	(_TIF_BLOCKSTEP|_TIF_NOTSC|_TIF_IO_BITMAP|
         _TIF_NOCPUID|_TIF_USER_RETURN_NOTIFY))))
	return;

The USER_RETURN_NOTIFY could really use some sanity: it is a notifier
chain with a single in-kernel user, which is KVM on x86 only, but we
most likely will need to propagate the flag even if it ends up getting
specialized.

	-hpa