Re: [kvm-unit-tests PATCH v1 4/4] s390x: add a test for SIE without MSO/MSL

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

On 4/5/23 21:55, Nina Schoetterl-Glausch wrote:
> On Mon, 2023-03-27 at 10:21 +0200, Nico Boehr wrote:
>> Since we now have the ability to run guests without MSO/MSL, add a test
>> to make sure this doesn't break.
>>
>> Signed-off-by: Nico Boehr <nrb@linux.ibm.com>
>> ---

[...]

>> +static inline void force_exit_value(uint64_t val)
>> +{
>> +	asm volatile(
>> +		"	diag	%[val],0,0x9c\n"
>> +		: : [val] "d"(val)
>> +	);
>> +}
>> +
>> +__attribute__((section(".text"))) int main(void)
> 
> Why is the attribute necessary? I know all the snippets have it, but I don't see
> why it's necessary.
> @Janosch ?

"Historical growth" :)

If it doesn't work without it then we need to find a way to fix it.
If it does work without it then we should remove the attribute from all 
snippets.

But this issue is a low priority for me.

> 
>> +{
>> +	uint8_t *invalid_ptr;
>> +
>> +	memset(test_page, 0, sizeof(test_page));
>> +	/* tell the host the page's physical address (we're running DAT off) */
>> +	force_exit_value((uint64_t)test_page);
>> +
>> +	/* write some value to the page so the host can verify it */
>> +	for (size_t i = 0; i < TEST_PAGE_COUNT; i++)
>> +		test_page[i * PAGE_SIZE] = 42 + i;
>> +
>> +	/* indicate we've written all pages */
>> +	force_exit();
>> +
>> +	/* the first unmapped address */
>> +	invalid_ptr = (uint8_t *)(TOTAL_PAGE_COUNT * PAGE_SIZE);
> 
> Why not just use an address high enough you know it will not be mapped?
> -1 should do just fine.
> 
>> +	*invalid_ptr = 42;
>> +
>> +	/* indicate we've written the non-allowed page (should never get here) */
>> +	force_exit();
>> +
>> +	return 0;
>> +}
>> diff --git a/s390x/unittests.cfg b/s390x/unittests.cfg
>> index d97eb5e943c8..aab0e670f2d4 100644
>> --- a/s390x/unittests.cfg
>> +++ b/s390x/unittests.cfg
>> @@ -215,3 +215,6 @@ file = migration-skey.elf
>>   smp = 2
>>   groups = migration
>>   extra_params = -append '--parallel'
>> +
>> +[sie-dat]
>> +file = sie-dat.elf
>