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Date: Thu, 06 Mar 2014 06:34:32 -0800 From: "H. Peter Anvin" <hpa@...or.com> To: Thomas Gleixner <tglx@...utronix.de>, Peter Zijlstra <peterz@...radead.org> CC: Rasmus Villemoes <linux@...musvillemoes.dk>, Khalid Aziz <khalid.aziz@...cle.com>, Ingo Molnar <mingo@...nel.org>, akpm@...ux-foundation.org, andi.kleen@...el.com, rob@...dley.net, viro@...iv.linux.org.uk, oleg@...hat.com, venki@...gle.com, linux-kernel@...r.kernel.org Subject: Re: [RFC] [PATCH] Pre-emption control for userspace The no checking is omitting access_ok(), no? Either way, disabling page faults have to be done explicitly. On March 6, 2014 6:33:04 AM PST, Thomas Gleixner <tglx@...utronix.de> wrote: > > >On Thu, 6 Mar 2014, Peter Zijlstra wrote: > >> On Thu, Mar 06, 2014 at 02:45:00PM +0100, Rasmus Villemoes wrote: >> > Peter Zijlstra <peterz@...radead.org> writes: >> > >> > > On Thu, Mar 06, 2014 at 02:24:43PM +0100, Rasmus Villemoes wrote: >> > >> Is it possible to implement non-sleeping versions of >{get,put}_user()? >> > > >> > > __{get,put}_user() >> > >> > Huh? >> > >> > arch/x86/include/asm/uaccess.h: >> > >> > /** >> > * __get_user: - Get a simple variable from user space, with less >checking. >> > * @x: Variable to store result. >> > * @ptr: Source address, in user space. >> > * >> > * Context: User context only. This function may sleep. >> > >> > What am I missing? >> >> __get_user() -> __get_user_nocheck() -> __get_user_size() -> >__get_user_asm() >> >> And __get_user_asm() seems to generate the required .fixup section >for >> this to work in pagefault_disable() context. > >Well, it still might sleep if you're using it in page fault enabled >context. So the documentation of that function sucks. > >Thanks, > > tglx -- Sent from my mobile phone. Please pardon brevity and lack of formatting. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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