Re: [kvm-unit-tests PATCH v2 3/3] lib: s390x: better smp interrupt checks

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

On 6/24/22 16:45, Claudio Imbrenda wrote:
> Use per-CPU flags and callbacks for Program and Extern 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.
> 
> This will significantly improve error reporting and debugging when
> things go wrong.
> 
> Both program interrupts and extern interrupts are now CPU-bound, even
> though some extern interrupts are floating (notably, the SCLP
> interrupt). In those cases, the testcases should mask interrupts and/or
> expect them appropriately according to need.
> 
> Signed-off-by: Claudio Imbrenda <imbrenda@linux.ibm.com>
> ---
>   lib/s390x/asm/arch_def.h | 17 +++++++++++-
>   lib/s390x/smp.h          |  8 +-----
>   lib/s390x/interrupt.c    | 57 +++++++++++++++++++++++++++++-----------
>   lib/s390x/smp.c          | 11 ++++++++
>   4 files changed, 70 insertions(+), 23 deletions(-)
[...]
>   
> +struct lowcore *smp_get_lowcore(uint16_t idx)
> +{
> +	if (THIS_CPU->idx == idx)
> +		return &lowcore;
> +
> +	check_idx(idx);
> +	return cpus[idx].lowcore;
> +}

This function is unused.

> +
>   int smp_sigp(uint16_t idx, uint8_t order, unsigned long parm, uint32_t *status)
>   {
>   	check_idx(idx);
> @@ -253,6 +262,7 @@ static int smp_cpu_setup_nolock(uint16_t idx, struct psw psw)
>   
>   	/* Copy all exception psws. */
>   	memcpy(lc, cpus[0].lowcore, 512);
> +	lc->this_cpu = cpus + idx;

Why not:
lc->this_cpu = &cpus[idx];

>   
>   	/* Setup stack */
>   	cpus[idx].stack = (uint64_t *)alloc_pages(2);
> @@ -325,6 +335,7 @@ void smp_setup(void)
>   	for (i = 0; i < num; i++) {
>   		cpus[i].addr = entry[i].address;
>   		cpus[i].active = false;
> +		cpus[i].idx = i;
>   		/*
>   		 * Fill in the boot CPU. If the boot CPU is not at index 0,
>   		 * swap it with the one at index 0. This guarantees that the