Re: [kvm-unit-tests PATCH v1 3/4] s390x: lib: sie: don't reenter SIE on pgm int

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

On 3/27/23 10:21, Nico Boehr wrote:
> At the moment, when a PGM int occurs while in SIE, we will just reenter
> SIE after the interrupt handler was called.
> 
> This is because sie() has a loop which checks icptcode and re-enters SIE
> if it is zero.
> 
> However, this behaviour is quite undesirable for SIE tests, since it
> doesn't give the host the chance to assert on the PGM int. Instead, we
> will just re-enter SIE, on nullifing conditions even causing the
> exception again.
> 
> Add a flag PROG_PGM_IN_SIE set by the pgm int fixup which indicates a
> program interrupt has occured in SIE. Check for the flag in sie() and if
> it's set return from sie() to give the host the ability to react on the
> exception. The host may check if a PGM int has occured in the guest
> using the new function sie_had_pgm_int().

We could simply check "!lowcore.pgm_int_code" by introducing:
uint16_t read_pgm_int(void)
{
	mb();
	return lowcore.pgm_int_code;
}

into interrupt.c.


Or to be a bit more verbose:
I don't see a reason why we'd want to store a per sblk PGM in SIE bit 
when all we want to know is either: was there a PGM at all (to stop the 
SIE loop) or was there a PGM between the expect and the 
check_pgm_int_code().