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

[Alexander Graf]

On 07.07.2012, at 10:39, Caraman Mihai Claudiu-B02008 wrote:

>> ________________________________________
>> From: Alexander Graf address@hidden
>> Sent: Saturday, July 07, 2012 2:11 AM
>> To: Caraman Mihai Claudiu-B02008
>> Cc: Benjamin Herrenschmidt; <address@hidden>; KVM list; linuxppc-dev; 
>> address@hidden 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:address@hidden
>>>> Sent: Thursday, July 05, 2012 1:26 AM
>>>> To: Alexander Graf
>>>> Cc: Caraman Mihai Claudiu-B02008; <address@hidden>; KVM list;
>>>> linuxppc-dev; address@hidden 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:

Ah, makes sense, yes.

> 
> #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); \

Or just free up another register early on, like here.


Alex

> +     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
> --
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