Re: [kvm-unit-tests PATCH v5 01/10] s390x: saving regs for interrupts

[Janosch Frank <frankja@linux.ibm.com>]

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On 2/20/20 1:00 PM, Pierre Morel wrote:
> If we use multiple source of interrupts, for example, using SCLP
> console to print information while using I/O interrupts, we need
> to have a re-entrant register saving interruption handling.
> 
> Instead of saving at a static memory address, let's save the base
> registers and the floating point registers on the stack.
> 
> Note that we keep the static register saving to recover from the
> RESET tests.
> 
> Signed-off-by: Pierre Morel <pmorel@linux.ibm.com>
> ---
>  s390x/cstart64.S | 23 +++++++++++++++++++++--
>  1 file changed, 21 insertions(+), 2 deletions(-)
> 
> diff --git a/s390x/cstart64.S b/s390x/cstart64.S
> index 9af6bb3..45da523 100644
> --- a/s390x/cstart64.S
> +++ b/s390x/cstart64.S
> @@ -118,6 +118,25 @@ memsetxc:
>  	lmg	%r0, %r15, GEN_LC_SW_INT_GRS
>  	.endm
>  
> +/* Save registers on the stack, so we can have stacked interrupts. */
> +	.macro SAVE_IRQ_REGS
> +	slgfi   %r15, 15 * 8
> +	stmg    %r0, %r14, 0(%r15)

So this is just making some space on the stack and storing r0 - r14, right?

Same is done for the floating point registers below.

Could you add a comment above slgfi and stmg and explain what they do?
A few words are enough.

> +	slgfi   %r15, 16 * 8
> +	.irp i, 0,1,2,3,4,5,6,7,8,9,10,11,12,13,14,15
> +	std	\i, \i * 8(%r15)
> +	.endr
> +	.endm
> +
> +	.macro RESTORE_IRQ_REGS
> +	.irp i, 0,1,2,3,4,5,6,7,8,9,10,11,12,13,14,15
> +	ld	\i, \i * 8(%r15)
> +	.endr
> +	algfi   %r15, 16 * 8
> +	lmg     %r0, %r14, 0(%r15)
> +	algfi   %r15, 15 * 8
> +	.endm
> +
>  .section .text
>  /*
>   * load_reset calling convention:
> @@ -182,9 +201,9 @@ mcck_int:
>  	lpswe	GEN_LC_MCCK_OLD_PSW
>  
>  io_int:
> -	SAVE_REGS
> +	SAVE_IRQ_REGS
>  	brasl	%r14, handle_io_int
> -	RESTORE_REGS
> +	RESTORE_IRQ_REGS
>  	lpswe	GEN_LC_IO_OLD_PSW
>  
>  svc_int:
> 



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