Re: [PATCH 4/6] target/i386: Add feature dependencies for AVX10

[Paolo Bonzini <pbonzini@redhat.com>]

On 10/28/24 11:02, Tao Su wrote:
> On Mon, Oct 28, 2024 at 09:45:39AM +0100, Paolo Bonzini wrote:
>> On 10/28/24 03:45, Tao Su wrote:
>>> Since the highest supported vector length for a processor implies that
>>> all lesser vector lengths are also supported, add the dependencies of
>>> the supported vector lengths. If all vector lengths aren't supported,
>>> clear AVX10 enable bit as well.
>>>
>>> Note that the order of AVX10 related dependencies should be kept as:
>>>           CPUID_24_0_EBX_AVX10_128     -> CPUID_24_0_EBX_AVX10_256,
>>>           CPUID_24_0_EBX_AVX10_256     -> CPUID_24_0_EBX_AVX10_512,
>>>           CPUID_24_0_EBX_AVX10_VL_MASK -> CPUID_7_1_EDX_AVX10,
>>
>> I think you need to add a set of dependencies so that avx10 cannot be set,
>> unless all the older AVX features that it's composed of are available.  From
>> the manual these are
>>
>> AVX512F, AVX512CD, AVX512VW, AVX512DQ, AVX512_VBMI, AVX512_IFMA,
>> AVX512_VNNI, AVX512_BF16, AVX512_VPOPCNTDQ, AVX512_VBMI2, VAES, GFNI,
>> VPCLMULQDQ, AVX512_BITALG, AVX512_FP16.
> 
> Thanks for such a quick review!!
> 
> AVX10.1 spec said:
> Intel AVX-512 will continue to be supported on P-core-only processors for
> the foreseeable future to support legacy applications. However, new vector
> ISA features will only be added to the Intel AVX10 ISA moving forward.
> While Intel AVX10/512 includes all Intel AVX-512 instructions, it
> important to note that applications compiled to Intel AVX-512 with vector
> length limited to 256 bits are not guaranteed to be compatible on an Intel
> AVX10/256 processor.
> 
> I.e. AVX10/256 processors will support old AVX-512 instructions
> (limited to 256 bits and enumerated by AVX10) but not set AVX-512 related
> CPUIDs. So, I think we can't add these dependencies…

Of course you're right about AVX10 in general, you still need to add the 
dependency but only for CPUID_24_0_EBX_AVX10_512.

Paolo