Re: [kvm-unit-tests PATCH v1 2/2] lib: s390x: better smp interrupt checks

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

On 6/3/22 17:40, Claudio Imbrenda wrote:
> Use per-CPU flags and callbacks for Program, Extern, and I/O interrupts
> instead of global variables.
> 
> This allows for more accurate error handling; a CPU waiting for an
> interrupt will not have it "stolen" by a different CPU that was not
> supposed to wait for one, and now two CPUs can wait for interrupts at
> the same time.
> 
> Signed-off-by: Claudio Imbrenda <imbrenda@linux.ibm.com>
> ---
>   lib/s390x/asm/arch_def.h |  7 ++++++-
>   lib/s390x/interrupt.c    | 38 ++++++++++++++++----------------------
>   2 files changed, 22 insertions(+), 23 deletions(-)
> 
> diff --git a/lib/s390x/asm/arch_def.h b/lib/s390x/asm/arch_def.h
> index 72553819..3a0d9c43 100644
> --- a/lib/s390x/asm/arch_def.h
> +++ b/lib/s390x/asm/arch_def.h
> @@ -124,7 +124,12 @@ struct lowcore {
>   	uint8_t		pad_0x0280[0x0308 - 0x0280];	/* 0x0280 */
>   	uint64_t	sw_int_crs[16];			/* 0x0308 */
>   	struct psw	sw_int_psw;			/* 0x0388 */
> -	uint8_t		pad_0x0310[0x11b0 - 0x0398];	/* 0x0398 */
> +	uint32_t	pgm_int_expected;		/* 0x0398 */
> +	uint32_t	ext_int_expected;		/* 0x039c */
> +	void		(*pgm_cleanup_func)(void);	/* 0x03a0 */
> +	void		(*ext_cleanup_func)(void);	/* 0x03a8 */
> +	void		(*io_int_func)(void);		/* 0x03b0 */
> +	uint8_t		pad_0x03b8[0x11b0 - 0x03b8];	/* 0x03b8 */

Before we directly pollute the lowcore I'd much rather have a pointer to 
a struct. We could then either use any area of the lowcore by adding a 
union or we extend the SMP lib per-cpu structs.

I don't want to have to review offset calculations for every change of 
per-cpu data. They are just way too easy to get wrong.