Re: [kvm-unit-tests PATCH] s390x/intercept: Test invalid prefix argument to SET PREFIX

[Janis Schoetterl-Glausch <scgl@linux.ibm.com>]

On 6/27/22 14:52, Claudio Imbrenda wrote:
> On Mon, 27 Jun 2022 14:43:56 +0200
> Janis Schoetterl-Glausch <scgl@linux.ibm.com> wrote:
> 
>> According to the architecture, SET PREFIX must try to access the new
>> prefix area and recognize an addressing exception if the area is not
>> accessible.
>> Test that the exception occurs when we try to set a prefix higher
>> than the available memory.
>>
>> Signed-off-by: Janis Schoetterl-Glausch <scgl@linux.ibm.com>
>> ---
>>  s390x/intercept.c | 14 ++++++++++++++
>>  1 file changed, 14 insertions(+)
>>
>> diff --git a/s390x/intercept.c b/s390x/intercept.c
>> index 86e57e11..0b90e588 100644
>> --- a/s390x/intercept.c
>> +++ b/s390x/intercept.c
>> @@ -74,6 +74,20 @@ static void test_spx(void)
>>  	expect_pgm_int();
>>  	asm volatile(" spx 0(%0) " : : "r"(-8L));
>>  	check_pgm_int_code(PGM_INT_CODE_ADDRESSING);
>> +
>> +	new_prefix = get_ram_size() & 0x7fffe000;
>> +	if (get_ram_size() - new_prefix < 2 * PAGE_SIZE) {
>> +		expect_pgm_int();
>> +		asm volatile("spx	%0 " : : "Q"(new_prefix));
>> +		check_pgm_int_code(PGM_INT_CODE_ADDRESSING);
>> +
>> +		/*
>> +		 * Cannot test inaccessibility of the second page the same way.
>> +		 * If we try to use the last page as first half of the prefix
>> +		 * area and our ram size is a multiple of 8k, after SPX aligns
>> +		 * the address to 8k we have a completely accessible area.
>> +		 */
>> +	}
> 
> please add something like:
> 
> else {
> 	report_skip("Inaccessible prefix");
> }
> 

Yeah, good idea.

Is there any low effort way of generating an invalid prefix other than > ram_size ?
That might then allow for testing the second page also.

>>  }
>>  
>>  /* Test the STORE CPU ADDRESS instruction */
>>
>> base-commit: 110c69492b53f0070e1bbce986fb635e72a423b4
>