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

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

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On 7/7/20 1:45 PM, David Hildenbrand wrote:
> 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.
> 

Well we also already have a check for zvm 6 with stsi 3.2.2 in skey.c
I'm not completely convinced that I want to loose two pages and a few
cycles on every startup for two separate test cases.



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