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

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

On 3/17/23 11:51, Nina Schoetterl-Glausch wrote:
> 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.
ahhh, right.

>> Looking at the file itself some asm blocks have no space before the "("
>> and some have one.
> 
> In spec_ex.c? Where?

Should have said: "after the (" but seems like the point doesn't matter 
anyway just fixup the xgr.

> 
>>
>>> +"	. = . + 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 },
>>
>