RE: [Qemu-ppc] [RFC PATCH 12/17] PowerPC: booke64: Add DO_KVM kernel hooks

[Caraman Mihai Claudiu-B02008 <B02008@freescale.com>]

>________________________________________
>From: Alexander Graf [agraf@suse.de]
>Sent: Saturday, July 07, 2012 2:11 AM
>To: Caraman Mihai Claudiu-B02008
>Cc: Benjamin Herrenschmidt; <kvm-ppc@vger.kernel.org>; KVM list; linuxppc-dev; qemu-ppc@nongnu.org List
>Subject: Re: [Qemu-ppc] [RFC PATCH 12/17] PowerPC: booke64: Add DO_KVM kernel hooks
>
>On 07.07.2012, at 00:33, Caraman Mihai Claudiu-B02008 wrote:
>
>>> -----Original Message-----
>>> From: Benjamin Herrenschmidt [mailto:benh@kernel.crashing.org]
>>> Sent: Thursday, July 05, 2012 1:26 AM
>>> To: Alexander Graf
>>> Cc: Caraman Mihai Claudiu-B02008; <kvm-ppc@vger.kernel.org>; KVM list;
>>> linuxppc-dev; qemu-ppc@nongnu.org List
>>> Subject: Re: [Qemu-ppc] [RFC PATCH 12/17] PowerPC: booke64: Add DO_KVM
>>> kernel hooks
>>>
>>> You can't but in any case I don't see the point of the conditional here,
>>> we'll eventually have to load srr1 no ? We can move the load up to here
>>> in all cases or can't we ?
>>
>> I like the idea, but there is a problem with addition macros which may clobber
>> r11 and PROLOG_ADDITION_MASKABLE_GEN is such a case.
>
>Mike -v please :)

Ben suggested something like this:
	
 #define EXCEPTION_PROLOG(n, type, addition) \
 	mtspr SPRN_SPRG_##type##_SCRATCH,r13; /* get spare registers */ \
 	mfspr r13,SPRN_SPRG_PACA; /* get PACA */ \
 	std r10,PACA_EX##type+EX_R10(r13); \
 	std r11,PACA_EX##type+EX_R11(r13); \
 	mfcr r10; /* save CR */ \	
+	mfspr r11,SPRN_##type##_SRR1;/* what are we coming from */ \
	DO_KVM	intnum,srr1; \
 	addition; /* additional code for that exc. */ \
 	std r1,PACA_EX##type+EX_R1(r13); /* save old r1 in the PACA */ \
 	stw r10,PACA_EX##type+EX_CR(r13); /* save old CR in the PACA */ \
-	mfspr r11,SPRN_##type##_SRR1;/* what are we coming from */ \
 	type##_SET_KSTACK; /* get special stack if necessary */\
 	andi. r10,r11,MSR_PR; /* save stack pointer */ \

But one of the addition looks like this:
	
 #define PROLOG_ADDITION_MASKABLE_GEN(n) \
 	lbz r11,PACASOFTIRQEN(r13); /* are irqs soft-disabled ? */ \
	cmpwi cr0,r11,0; /* yes -> go out of line */ \
	beq masked_interrupt_book3e_##n	

So for maskable gen we end up with:

 #define EXCEPTION_PROLOG(n, type, addition) \
 	mtspr SPRN_SPRG_##type##_SCRATCH,r13; /* get spare registers */ \
 	mfspr r13,SPRN_SPRG_PACA; /* get PACA */ \
 	std r10,PACA_EX##type+EX_R10(r13); \
 	std r11,PACA_EX##type+EX_R11(r13); \
 	mfcr r10; /* save CR */ \
	mfspr r11,SPRN_##type##_SRR1;/* what are we coming from */ \
 	DO_KVM	intnum,srr1; \
	lbz r11,PACASOFTIRQEN(r13); /* are irqs soft-disabled ? */ \
	cmpwi cr0,r11,0; /* yes -> go out of line */ \
	beq masked_interrupt_book3e_##n	\
	std r1,PACA_EX##type+EX_R1(r13); /* save old r1 in the PACA */ \
 	stw r10,PACA_EX##type+EX_CR(r13); /* save old CR in the PACA */ \
 	type##_SET_KSTACK; /* get special stack if necessary */\
 	andi. r10,r11,MSR_PR; /* save stack pointer */ \
	
This affects the last asm line, we load srr1 into r11 but clobber it in-between.
We need a spare register for maskable gen addition. I think we can free r10 sooner
and used it in addition like this:

 #define EXCEPTION_PROLOG(n, type, addition) \
 	mtspr SPRN_SPRG_##type##_SCRATCH,r13; /* get spare registers */ \
 	mfspr r13,SPRN_SPRG_PACA; /* get PACA */ \		
 	std r10,PACA_EX##type+EX_R10(r13); \
 	std r11,PACA_EX##type+EX_R11(r13); \
+	mfspr r11,SPRN_##type##_SRR1;/* what are we coming from */ \
	mfcr r10; /* save CR */ \
+ 	stw r10,PACA_EX##type+EX_CR(r13); /* save old CR in the PACA */ \
 	DO_KVM	intnum,srr1; \
-	lbz r11,PACASOFTIRQEN(r13); /* are irqs soft-disabled ? */ \
-	cmpwi cr0,r11,0; /* yes -> go out of line */ \
+	lbz r10,PACASOFTIRQEN(r13); /* are irqs soft-disabled ? */ \
+	cmpwi cr0,r10,0; /* yes -> go out of line */ \
	beq masked_interrupt_book3e_##n	\
 	std r1,PACA_EX##type+EX_R1(r13); /* save old r1 in the PACA */ \
- 	stw r10,PACA_EX##type+EX_CR(r13); /* save old CR in the PACA */ \
-	mfspr r11,SPRN_##type##_SRR1;/* what are we coming from */ \
 	type##_SET_KSTACK; /* get special stack if necessary */\
 	andi. r10,r11,MSR_PR; /* save stack pointer */ \
	
-Mike