lkml.org 
[lkml]   [2015]   [Oct]   [6]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
SubjectRe: [PATCH v2 22/36] x86/entry: Add C code for fast system call entries
From
On Tue, Oct 6, 2015 at 9:25 AM, Linus Torvalds
<torvalds@linux-foundation.org> wrote:
>
>> + local_irq_enable();
>> + if (get_user(*(u32 *)&regs->cx,
>> + (u32 __user __force *)(unsigned long)(u32)regs->sp)) {
> ...
>> + local_irq_disable();
>
> this is expensive. Since we now do it in C code and can easily do
> this, why does the code not do this all with interrupts disabled,
> which is valid for user accesses but disables page faults, and then in
> the unlikely situation where that fails, we do it the slow and careful
> way?

Ok. I notice that then a later patch removes the local_irq_disable()
and calls do_syscall_32_irqs_on().

So I guess that "just run get_user with interrupts disabled"
optimization is pointless, because we'll just end up enabling
interrupts at some point anyway, and it can just be done before the
get_user().

So never mind.

Linus


\
 
 \ /
  Last update: 2015-10-06 10:41    [W:0.658 / U:0.140 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site