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 09:00:48 +0200
From:   Christophe Leroy <christophe.leroy@....fr>
To:     Paul Mackerras <paulus@...abs.org>
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



Le 23/05/2019 à 08:14, Paul Mackerras a écrit :
> 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:

Is that a standard defconfig ? If not, can you provide your .config ?

> 
> 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.

This SYSCALL_ENTRY macro is a slimmed version of NORMAL_EXCEPTION_PROLOG()

In NORMAL_EXCEPTION_PROLOG(), we have:
	DO_KVM	BOOKE_INTERRUPT_##intno SPRN_SRR1;	

The _SPRN_SRR1 comes from there


Then in /arch/powerpc/include/asm/kvm_booke_hv_asm.h:

.macro DO_KVM intno srr1
#ifdef CONFIG_KVM_BOOKE_HV
BEGIN_FTR_SECTION
	mtocrf	0x80, r11	/* check MSR[GS] without clobbering reg */
	bf	3, 1975f
	b	kvmppc_handler_\intno\()_\srr1
1975:
END_FTR_SECTION_IFSET(CPU_FTR_EMB_HV)
#endif
.endm


Christophe