Re: [kvm-unit-tests v2 PATCH] s390x/cpumodel: The missing DFP facility on TCG is expected

[David Hildenbrand <david@redhat.com>]

On 07.07.20 13:44, Cornelia Huck wrote:
> On Tue,  7 Jul 2020 12:42:05 +0200
> Thomas Huth <thuth@redhat.com> wrote:
> 
>> When running the kvm-unit-tests with TCG on s390x, the cpumodel test
>> always reports the error about the missing DFP (decimal floating point)
>> facility. This is kind of expected, since DFP is not required for
>> running Linux and thus nobody is really interested in implementing
>> this facility in TCG. Thus let's mark this as an expected error instead,
>> so that we can run the kvm-unit-tests also with TCG without getting
>> test failures that we do not care about.
>>
>> Signed-off-by: Thomas Huth <thuth@redhat.com>
>> ---
>>  v2:
>>  - Rewrote the logic, introduced expected_tcg_fail flag
>>  - Use manufacturer string instead of VM name to detect TCG
>>
>>  s390x/cpumodel.c | 49 ++++++++++++++++++++++++++++++++++++++++++------
>>  1 file changed, 43 insertions(+), 6 deletions(-)
> 
> (...)
> 
>> +static bool is_tcg(void)
>> +{
>> +	const char qemu_ebcdic[] = { 0xd8, 0xc5, 0xd4, 0xe4 };
>> +	bool ret = false;
>> +	uint8_t *buf;
>> +
>> +	buf = alloc_page();
>> +	if (!buf)
>> +		return false;
>> +
>> +	if (stsi(buf, 1, 1, 1)) {
>> +		goto out;
>> +	}
> 
> This does an alloc_page() and a stsi() every time you call it...
> 
>> +
>> +	/*
>> +	 * If the manufacturer string is "QEMU" in EBCDIC, then we are on TCG
>> +	 * (otherwise the string is "IBM" in EBCDIC)
>> +	 */
>> +	if (!memcmp(&buf[32], qemu_ebcdic, sizeof(qemu_ebcdic)))
>> +		ret =  true;
>> +out:
>> +	free_page(buf);
>> +	return ret;
>> +}
>> +
>> +
>>  int main(void)
>>  {
>>  	int i;
>> @@ -46,11 +81,13 @@ int main(void)
>>  
>>  	report_prefix_push("dependency");
> 
> ...so maybe cache the value for is_tcg() here instead of checking
> multiple times in the loop?

Maybe move it to common code and do the detection early during boot? The
n provide is_tcg() or sth. like that. Could be helpful in other context
maybe.


-- 
Thanks,

David / dhildenb