Subject: Re: [PATCH v2] powerpc/64: system call implement the bulk of the logic in C

From: Michael Ellerman <[email-masked]>
Date: Thu, 05 Sep 2019 14:14:38 +1000

Nicholas Piggin <[email-masked]> writes:
> System call entry and particularly exit code is beyond the limit of what
> is reasonable to implement in asm.
>
> This conversion moves all conditional branches out of the asm code,
> except for the case that all GPRs should be restored at exit.
>
> Null syscall test is about 5% faster after this patch, because the exit
> work is handled under local_irq_disable, and the hard mask and pending
> interrupt replay is handled after that, which avoids games with MSR.
>
> Signed-off-by: Nicholas Piggin <[email-masked]>
> ---
> Since v1:
> - Fix big endian build (mpe)
> - Fix order of exit tracing to after the result registers have been set.
> - Move ->softe store before MSR[EE] is set, fix the now obsolete comment.
> - More #ifdef tidyups and writing the accounting helpers nicer (Christophe)
> - Minor things like move the TM debug store into C

This doesn't build in a few configs.

It needed:

+#else
+static inline void kuap_check_amr(void) { }

In kup-radix.h to fix the KUAP=n build.

It still fails to build on ppc64e with:

  arch/powerpc/kernel/syscall_64.c:161:2: error: implicit declaration of function '__mtmsrd' [-Werror=implicit-function-declaration]

  http://kisskb.ellerman.id.au/kisskb/buildresult/13946972/

Which I haven't debugged yet.

cheers