Re: [patch V4 part 3 01/29] x86/traps: Mark fixup_bad_iret() noinstr

Mathieu Desnoyers
2020-05-14T00:41:51Z

----- On May 12, 2020, at 9:51 PM, rostedt rostedt@goodmis.org wrote:

> On Fri, 8 May 2020 17:39:00 -0700
> Andy Lutomirski <luto@kernel.org> wrote:
>
>> On Tue, May 5, 2020 at 7:15 AM Thomas Gleixner <tglx@linutronix.de> wrote:
>> >
>> > This is called from deep entry ASM in a situation where instrumentation
>> > will cause more harm than providing useful information.
>> >
>>
>> Acked-by: Andy Lutomirski <luto@kernel.org>
>>
>> Maybe add to changelog:
>>
>> Switch from memmove() to memcpy() because memmove() can't be called
>> from noinstr code.
>
> Yes please, because I was about to say that there was changes that
> didn't seem to fit the change log.
>
> I would also add a comment in the code saying that we need the temp
> variable to use memcpy as memmove can't be used in noinstr code.

Looking at an updated version of the tree, I see the acked-by from Andy,
but not comment about switching from memmove to memcpy.

Also, I notice a significant undocumented change in this patch: it changes
a this_cpu_read() (which presumes preemption is enabled) to a __this_cpu_read().

So the 100$ question: is preemption enabled or not in fixup_bad_iret() ? And of
course that change should be documented in the commit message.

Thanks,

Mathieu

--
Mathieu Desnoyers
EfficiOS Inc.