Re: [patch V2 08/17] x86/entry: Move syscall irq tracing to C code

Andy Lutomirski
2019-10-24T16:24:13Z

On Wed, Oct 23, 2019 at 2:30 PM Andy Lutomirski <luto@kernel.org> wrote:
>
> On Wed, Oct 23, 2019 at 5:31 AM Thomas Gleixner <tglx@linutronix.de> wrote:
> >
> > Interrupt state tracing can be safely done in C code. The few stack
> > operations in assembly do not need to be covered.
> >
> > Remove the now pointless indirection via .Lsyscall_32_done and jump to
> > swapgs_restore_regs_and_return_to_usermode directly.
>
> This doesn't look right.

Well, I feel a bit silly. I read this:

>
> > #define SYSCALL_EXIT_WORK_FLAGS \
> > @@ -279,6 +282,9 @@ static void syscall_slow_exit_work(struc

^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

and I applied the diff in my head to the wrong function, and I didn't
notice that it didn't really apply there. Oddly, gitweb gets this
right:

https://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git/commit/?h=WIP.core/entry&id=e3158f93138ded84eb44fa97606197f6adcf9366

Looking at the actual code:

Acked-by: Andy Lutomirski <luto@kernel.org>

with one minor caveat: you are making a subtle and mostly irrelevant
semantic change: with your patch, user mode will be traced as IRQs on
even if a nasty user has used iopl() to turn off interrupts. This is
probably a good thing, but I think you should mention it in the
changelog.

FWIW, the rest of the series looks pretty good, too.