[PATCH] powerpc/64s: Use relon prolog for EXC_VIRT_OOL_MASKABLE_HV handlers

[Michael Ellerman]

Nicholas Piggin <npiggin at gmail.com> writes:

> Hypervisor Virtualization and Directed Hypervisor Doorbell interrupt
> handlers use the macro EXC_VIRT_OOL_MASKABLE_HV for their relocation-on
> handlers, which calls MASKABLE_RELON_EXCEPTION_HV_OOL, which uses the
> real mode interrupt prolog.
>
> Use the RELON variant instead to reduce overhead.
>
> Fixes: 1707dd1613 ("powerpc: Save CFAR before branching in interrupt entry paths")
> Cc: Paul Mackerras <paulus at samba.org>
> Signed-off-by: Nicholas Piggin <npiggin at gmail.com>
> ---
>
> I was hesitant about using the Fixes: tag on this one because it's not
> a correctness bug as far as I can see.

Fixes can just mean "if you have this other commit you'll most likely
want this one too".

You can clarify the degree of Fixness in the change log, which then
allows a backporter to decide if they want it or not.

In this case I think it's entirely right, this is a fairly unfortunate
bug from a performance point of view if I'm reading it right.

cheers

> diff --git a/arch/powerpc/include/asm/exception-64s.h b/arch/powerpc/include/asm/exception-64s.h
> index 14752eee3d0c..b89c91e27dd0 100644
> --- a/arch/powerpc/include/asm/exception-64s.h
> +++ b/arch/powerpc/include/asm/exception-64s.h
> @@ -522,7 +522,7 @@ END_FTR_SECTION_NESTED(ftr,ftr,943)
>  
>  #define MASKABLE_RELON_EXCEPTION_HV_OOL(vec, label)			\
>  	EXCEPTION_PROLOG_1(PACA_EXGEN, SOFTEN_TEST_HV, vec);		\
> -	EXCEPTION_PROLOG_PSERIES_1(label, EXC_HV)
> +	EXCEPTION_RELON_PROLOG_PSERIES_1(label, EXC_HV)
>  
>  /*
>   * Our exception common code can be passed various "additions"
> -- 
> 2.11.0