Re: [PATCH v3 19/22] x86emul: support TILELOADD{,T1} and TILESTORE

[Jan Beulich <jbeulich@xxxxxxxx>]

On 26.04.2021 09:12, Paul Durrant wrote:
> On 22/04/2021 16:11, Jan Beulich wrote:
>> On 22.04.2021 17:06, Jan Beulich wrote:
>>> On 22.04.2021 16:55, Jan Beulich wrote:
>>>> +        do {
>>>> +            /* Limit rows to just as many to cover the next one to 
>>>> access. */
>>>> +            cfg->start_row = i;
>>>> +            cfg->rows[modrm_reg] = i + 1;
>>>> +            write_tilecfg(cfg);
>>>> +
>>>> +            if ( vex.pfx != vex_f3 )
>>>> +                rc = ops->read(ea.mem.seg,
>>>> +                               truncate_ea(ea.mem.off + i * ea.val),
>>>> +                               row, cfg->colsb[modrm_reg], ctxt);
>>>> +
>>>> +            invoke_stub("", "", "=m" (dummy) : "a" (row));
>>>> +
>>>> +            if ( vex.pfx == vex_f3 )
>>>> +                rc = ops->write(ea.mem.seg,
>>>> +                                truncate_ea(ea.mem.off + i * ea.val),
>>>> +                                row, cfg->colsb[modrm_reg], ctxt);
>>>> +        } while ( rc == X86EMUL_OKAY && ++i < n );
>>>
>>> in principle tiles could have rows larger than 64 bytes without any
>>> separate CPUID feature flag qualifying this. struct hvm_mmio_cache,
>>> otoh, is having a fixed-size 64-byte buffer right now. Therefore I'm
>>> wondering whether we'd want to switch to dynamically allocating that
>>> to the minimum of 64 bytes and the size of a tile row, just as a
>>> precautionary measure.
>>
>> Actually, as it occurred to me only after sending, enlarging tile size
>> would under almost all circumstances require a new XSTATE component,
>> which we'd need to enable first. I consider it less likely that they'd
>> permit a wider range of layouts without increasing tile size. But we
>> might still want to play safe.
>>
> 
> I guess on-demand reallocation to a larger size would be fine. Certainly 
> we want to be sure we don't overflow.

Okay, I've added a patch doing not just this, but (perhaps even more
important) also increase struct hvmemul_cache's capacity on such
hardware.

Jan