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Date: Thu, 18 Feb 2016 19:51:16 +0100 From: Ingo Molnar <mingo@...nel.org> To: Linus Torvalds <torvalds@...ux-foundation.org> Cc: Tony Luck <tony.luck@...el.com>, Linux Kernel Mailing List <linux-kernel@...r.kernel.org>, Peter Zijlstra <a.p.zijlstra@...llo.nl>, Thomas Gleixner <tglx@...utronix.de>, "H. Peter Anvin" <hpa@...or.com> Subject: Re: [PATCH v11 3/4] x86, mce: Add __mcsafe_copy() * Linus Torvalds <torvalds@...ux-foundation.org> wrote: > On Wed, Feb 17, 2016 at 10:20 AM, Tony Luck <tony.luck@...el.com> wrote: > > > > If we faulted during the copy, then 'trapnr' will say which type > > of trap (X86_TRAP_PF or X86_TRAP_MC) and 'remain' says how many > > bytes were not copied. > > So apart from the naming, a couple of questions: > > - I'd like to see the actual *use* case explained, not just what it does. > > - why does this use the complex - and slower, on modern machines - > unrolled manual memory copy, when you might as well just use a single > > rep ; movsb > > which not only makes it smaller, but makes the exception fixup trivial. > > - why not make the "bytes remaining" the same as for a user-space > copy (ie return it as the return value)? > > - at that point, it ends up looking a *lot* like uaccess_try/catch, > which gets the error code from current_thread_info()->uaccess_err > > Hmm? memcpy_try()/memcpy_catch() definitely has a nice ring to it. Thanks, Ingo
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