Re: [PATCH 4/8] s390/entry: workaround llvm's IAS limitations

From: Alexander Gordeev <agordeev@linux.ibm.com>
To: Heiko Carstens <hca@linux.ibm.com>
Cc: Nathan Chancellor <nathan@kernel.org>,
	Vasily Gorbik <gor@linux.ibm.com>,
	Jonas Paulsson <paulsson@linux.vnet.ibm.com>,
	Ulrich Weigand <ulrich.weigand@de.ibm.com>,
	Masahiro Yamada <masahiroy@kernel.org>,
	Alexander Egorenkov <egorenar@linux.ibm.com>,
	Sven Schnelle <svens@linux.ibm.com>,
	Andreas Krebbel <krebbel@linux.ibm.com>,
	Nathan Chancellor <natechancellor@gmail.com>,
	Nick Desaulniers <ndesaulniers@google.com>,
	linux-kernel@vger.kernel.org, linux-s390@vger.kernel.org
Subject: Re: [PATCH 4/8] s390/entry: workaround llvm's IAS limitations
Date: Mon, 16 May 2022 11:07:43 +0200	[thread overview]
Message-ID: <YoIUX864ULCwu4pz@tuxmaker.boeblingen.de.ibm.com> (raw)
In-Reply-To: <Yn1CyTcrZk1Kgvoq@osiris>

On Thu, May 12, 2022 at 07:24:25PM +0200, Heiko Carstens wrote:
> From fe4fb0b014378d84ae517deaea338577b2ea6ae0 Mon Sep 17 00:00:00 2001
> From: Heiko Carstens <hca@linux.ibm.com>
> Date: Sat, 7 May 2022 15:00:40 +0200
> Subject: [PATCH 3/7] s390/entry: workaround llvm's IAS limitations
> 
> llvm's integrated assembler cannot handle immediate values which are
> calculated with two local labels:
> 
> <instantiation>:3:13: error: invalid operand for instruction
>  clgfi %r14,.Lsie_done - .Lsie_gmap
> 
> Workaround this by adding clang specific code which reads the specific
> value from memory. Since this code is within the hot paths of the kernel
> and adds an additional memory reference, keep the original code, and add
> ifdef'ed code.
> 
> Signed-off-by: Heiko Carstens <hca@linux.ibm.com>
> ---
>  arch/s390/kernel/entry.S | 14 ++++++++++++--
>  1 file changed, 12 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/s390/kernel/entry.S b/arch/s390/kernel/entry.S
> index a6b45eaa3450..f2f30bfba1e9 100644
> --- a/arch/s390/kernel/entry.S
> +++ b/arch/s390/kernel/entry.S
> @@ -172,9 +172,19 @@ _LPP_OFFSET	= __LC_LPP
>  	lgr	%r14,\reg
>  	larl	%r13,\start
>  	slgr	%r14,%r13
> -	lghi	%r13,\end - \start
> -	clgr	%r14,%r13
> +#ifdef CONFIG_AS_IS_LLVM
> +	clgfrl	%r14,.Lrange_size\@

> +#else
> +	clgfi	%r14,\end - \start
> +#endif
>  	jhe	\outside_label
> +#ifdef CONFIG_CC_IS_CLANG
> +	.section .rodata, "a"
> +	.align 4
> +.Lrange_size\@:
> +	.long	\end - \start

Isn't the machine check handler refers to this memory before checking
unrecoverable storage errors (with CHKSTG macro) as result of this change?

> +	.previous
> +#endif
>  	.endm
>  
>  	.macro SIEEXIT
> -- 
> 2.32.0