Re: [PATCH v4 1/3] target-arm: Add support for Fujitsu A64FX

[Richard Henderson <richard.henderson@linaro.org>]

On 8/17/21 5:36 AM, Andrew Jones wrote:
> On Tue, Aug 17, 2021 at 05:23:17AM -1000, Richard Henderson wrote:
>> On 8/17/21 1:56 AM, Andrew Jones wrote:
>>> I guess it's fine. You could easily create a new cpu_arm_set_sve_vq()
>>> which would forbid changing the properties if you wanted to, but then
>>> we need to answer Peter's question in order to see if there's a
>>> precedent for that type of property.
>>
>> I don't see the point in read-only properties.  If the user wants to set
>> non-standard values on the command-line, let them.  What is most important
>> is getting the correct default from '-cpu a64fx'.
>>
> 
> So maybe we should just go ahead and add all sve* properties, but then
> make sure the default vq map is correct.

I think that's the right answer.

Presently we have a kvm_supported variable that's initialized by kvm_arm_sve_get_vls().  I 
think we want to rename that variable and provide a version of that function for tcg. 
Probably we should have done that before, with a trivial function for -cpu max to set all 
bits.

Then eliminate most of the other kvm_enabled() checks in arm_cpu_sve_finalize.  I think 
the only one we keep is the last, where we verify that the final sve_vq_map matches 
kvm_enabled exactly, modulo max_vq.

This should minimize the differences in behaviour between tcg and kvm.

r~