linux-kernel - Re: [PATCH v3 14/16] powerpc/32: implement fast entry for syscalls on BOOKE

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Date:   Thu, 23 May 2019 16:14:27 +1000
From:   Paul Mackerras <paulus@...abs.org>
To:     Christophe Leroy <christophe.leroy@....fr>
Cc:     Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Michael Ellerman <mpe@...erman.id.au>,
        Nicholas Piggin <npiggin@...il.com>,
        linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org
Subject: Re: [PATCH v3 14/16] powerpc/32: implement fast entry for syscalls
 on BOOKE

On Tue, Apr 30, 2019 at 12:39:03PM +0000, Christophe Leroy wrote:
> This patch implements a fast entry for syscalls.
> 
> Syscalls don't have to preserve non volatile registers except LR.
> 
> This patch then implement a fast entry for syscalls, where
> volatile registers get clobbered.
> 
> As this entry is dedicated to syscall it always sets MSR_EE
> and warns in case MSR_EE was previously off
> 
> It also assumes that the call is always from user, system calls are
> unexpected from kernel.

This is now upstream as commit 1a4b739bbb4f.  On the e500mc test
config that I use, I'm getting this build failure:

arch/powerpc/kernel/head_fsl_booke.o: In function `SystemCall':
arch/powerpc/kernel/head_fsl_booke.S:416: undefined reference to `kvmppc_handler_BOOKE_INTERRUPT_SYSCALL_SPRN_SRR1'
Makefile:1052: recipe for target 'vmlinux' failed

> +.macro SYSCALL_ENTRY trapno intno
> +	mfspr	r10, SPRN_SPRG_THREAD
> +#ifdef CONFIG_KVM_BOOKE_HV
> +BEGIN_FTR_SECTION
> +	mtspr	SPRN_SPRG_WSCRATCH0, r10
> +	stw	r11, THREAD_NORMSAVE(0)(r10)
> +	stw	r13, THREAD_NORMSAVE(2)(r10)
> +	mfcr	r13			/* save CR in r13 for now	   */
> +	mfspr	r11, SPRN_SRR1
> +	mtocrf	0x80, r11	/* check MSR[GS] without clobbering reg */
> +	bf	3, 1975f
> +	b	kvmppc_handler_BOOKE_INTERRUPT_\intno\()_SPRN_SRR1

It seems to me that the "_SPRN_SRR1" on the end of this line
isn't meant to be there...  However, it still fails to link with that
removed.

Paul.