Re: [PATCH 13/22] x86: FRED enumerations

[Jan Beulich <jbeulich@xxxxxxxx>]

On 14.08.2025 13:20, Jan Beulich wrote:
> On 08.08.2025 22:23, Andrew Cooper wrote:
>> --- a/xen/include/public/arch-x86/cpufeatureset.h
>> +++ b/xen/include/public/arch-x86/cpufeatureset.h
>> @@ -310,7 +310,10 @@ XEN_CPUFEATURE(ARCH_PERF_MON, 10*32+8) /*   
>> Architectural Perfmon */
>>  XEN_CPUFEATURE(FZRM,         10*32+10) /*A  Fast Zero-length REP MOVSB */
>>  XEN_CPUFEATURE(FSRS,         10*32+11) /*A  Fast Short REP STOSB */
>>  XEN_CPUFEATURE(FSRCS,        10*32+12) /*A  Fast Short REP CMPSB/SCASB */
>> +XEN_CPUFEATURE(FRED,         10*32+17) /*   Fast Return and Event Delivery 
>> */
>> +XEN_CPUFEATURE(LKGS,         10*32+18) /*   Load Kernel GS instruction */
>>  XEN_CPUFEATURE(WRMSRNS,      10*32+19) /*S  WRMSR Non-Serialising */
>> +XEN_CPUFEATURE(NMI_SRC,      10*32+20) /*   NMI-Source Reporting */
>>  XEN_CPUFEATURE(AMX_FP16,     10*32+21) /*   AMX FP16 instruction */
>>  XEN_CPUFEATURE(AVX_IFMA,     10*32+23) /*A  AVX-IFMA Instructions */
>>  XEN_CPUFEATURE(LAM,          10*32+26) /*   Linear Address Masking */
> 
> I'd like to note that we could long have had this if my long-pending emulator
> patch had gone in at some point.

Actually what I further have there, and what in the context of patch 15 I
notice you should have here is

--- a/xen/tools/gen-cpuid.py
+++ b/xen/tools/gen-cpuid.py
@@ -278,7 +278,8 @@ def crunch_numbers(state):
         # superpages, PCID and PKU are only available in 4 level paging.
         # NO_LMSL indicates the absense of Long Mode Segment Limits, which
         # have been dropped in hardware.
-        LM: [CX16, PCID, LAHF_LM, PAGE1GB, PKU, NO_LMSL, AMX_TILE, CMPCCXADD],
+        LM: [CX16, PCID, LAHF_LM, PAGE1GB, PKU, NO_LMSL, AMX_TILE, CMPCCXADD,
+             LKGS],
 
         # AMD K6-2+ and K6-III processors shipped with 3DNow+, beyond the
         # standard 3DNow in the earlier K6 processors.
@@ -347,6 +348,9 @@ def crunch_numbers(state):
         # computational instructions.  All further AMX features are built on 
top
         # of AMX-TILE.
         AMX_TILE: [AMX_BF16, AMX_INT8, AMX_FP16, AMX_COMPLEX],
+
+        # FRED builds on the LKGS instruction.
+        LKGS: [FRED],
     }
 
     deep_features = tuple(sorted(deps.keys()))

Jan