Re: [kvm-unit-tests PATCH v3 2/3] s390x/spec_ex: Add test introducing odd address into PSW

[Nina Schoetterl-Glausch <nsg@linux.ibm.com>]

On Fri, 2023-03-17 at 10:26 +0100, Janosch Frank wrote:
> On 3/15/23 16:54, Nina Schoetterl-Glausch wrote:
> > Instructions on s390 must be halfword aligned.
> > Introducing an odd instruction address into the PSW leads to a
> > specification exception when attempting to execute the instruction at
> > the odd address.
> > Add a test for this.
> > 
> > Signed-off-by: Nina Schoetterl-Glausch <nsg@linux.ibm.com>
> 
> Acked-by: Janosch Frank <frankja@linux.ibm.com>
> 
> Some nits below.
> 
> > ---
> >   s390x/spec_ex.c | 50 ++++++++++++++++++++++++++++++++++++++++++++++++-
> >   1 file changed, 49 insertions(+), 1 deletion(-)
> > 
> > diff --git a/s390x/spec_ex.c b/s390x/spec_ex.c
> > index 2adc5996..83b8c58e 100644
> > --- a/s390x/spec_ex.c
> > +++ b/s390x/spec_ex.c
> > @@ -88,12 +88,23 @@ static void expect_invalid_psw(struct psw psw)
> >   	invalid_psw_expected = true;
> >   }
> >   
> > +static void clear_invalid_psw(void)
> > +{
> > +	expected_psw = PSW(0, 0);
> > +	invalid_psw_expected = false;
> > +}
> > +
> >   static int check_invalid_psw(void)
> >   {
> >   	/* Since the fixup sets this to false we check for false here. */
> >   	if (!invalid_psw_expected) {
> > +		/*
> > +		 * Early exception recognition: pgm_int_id == 0.
> > +		 * Late exception recognition: psw address has been
> > +		 *	incremented by pgm_int_id (unpredictable value)
> > +		 */
> >   		if (expected_psw.mask == invalid_psw.mask &&
> > -		    expected_psw.addr == invalid_psw.addr)
> > +		    expected_psw.addr == invalid_psw.addr - lowcore.pgm_int_id)
> >   			return 0;
> >   		report_fail("Wrong invalid PSW");
> >   	} else {
> > @@ -112,6 +123,42 @@ static int psw_bit_12_is_1(void)
> >   	return check_invalid_psw();
> >   }
> >   
> > +extern char misaligned_code[];
> > +asm (  ".balign	2\n"
> 
> Is the double space intended?

Yes, so stuff lines up.
> Looking at the file itself some asm blocks have no space before the "(" 
> and some have one.

In spec_ex.c? Where?

> 
> > +"	. = . + 1\n"
> > +"misaligned_code:\n"
> > +"	larl	%r0,0\n"
> > +"	br	%r1\n"
> > +);
> 
> Any reason this is not indented?

You mean the whole asm block, so it looks more like a function body to the misaligned_code symbol?
I'm indifferent about it, can do that if you think it's nicer.

> 
> > +
> > +static int psw_odd_address(void)
> > +{
> > +	struct psw odd = PSW_WITH_CUR_MASK((uint64_t)&misaligned_code);
> > +	uint64_t executed_addr;
> > +
> > +	expect_invalid_psw(odd);
> > +	fixup_psw.mask = extract_psw_mask();
> > +	asm volatile ( "xr	%%r0,%%r0\n"
> 
> While it will likely never make a difference I'd still use xgr here 
> instead of xr.

Yes, needs xgr.
> 
> > +		"	larl	%%r1,0f\n"
> > +		"	stg	%%r1,%[fixup_addr]\n"
> > +		"	lpswe	%[odd_psw]\n"
> > +		"0:	lr	%[executed_addr],%%r0\n"
> > +	: [fixup_addr] "=&T" (fixup_psw.addr),
> > +	  [executed_addr] "=d" (executed_addr)
> > +	: [odd_psw] "Q" (odd)
> > +	: "cc", "%r0", "%r1"
> > +	);
> > +
> > +	if (!executed_addr) {
> > +		return check_invalid_psw();
> > +	} else {
> > +		assert(executed_addr == odd.addr);
> > +		clear_invalid_psw();
> > +		report_fail("did not execute unaligned instructions");
> > +		return 1;
> > +	}
> > +}
> > +
> >   /* A short PSW needs to have bit 12 set to be valid. */
> >   static int short_psw_bit_12_is_0(void)
> >   {
> > @@ -170,6 +217,7 @@ struct spec_ex_trigger {
> >   static const struct spec_ex_trigger spec_ex_triggers[] = {
> >   	{ "psw_bit_12_is_1", &psw_bit_12_is_1, false, &fixup_invalid_psw },
> >   	{ "short_psw_bit_12_is_0", &short_psw_bit_12_is_0, false, &fixup_invalid_psw },
> > +	{ "psw_odd_address", &psw_odd_address, false, &fixup_invalid_psw },
> >   	{ "bad_alignment", &bad_alignment, true, NULL },
> >   	{ "not_even", &not_even, true, NULL },
> >   	{ NULL, NULL, false, NULL },
>