Il mer 19 nov 2025, 08:12 Zhao Liu <[email protected]> ha scritto: > > > Note, APX_NCI_NDD_NF is documented as always enabled for Intel > > > processors since APX spec (revision v7.0). Now any Intel processor > > > that enumerates support for APX_F (CPUID.(EAX=0x7, ECX=1).EDX[21]) > > > will also enumerate support for APX_NCI_NDD_NF. > > This sentence (from APX spec rev.7) emphasizes the “Intel” vendor, > and its primary goal was to address and explain compatibility concern > for pre-enabling work based on APX spec v6. Prior to v7, APX included > NCI_NDD_NF by default, but this feature has now been separated from > basic APX and requires explicit checking CPUID bit. > > x86 ecosystem advisory group has aligned on APX so it may be possible > for other x86 vendors to implement APX without NCI_NDD_NF and this still > match with the APX spec. >
Oh, I was not aware of that. It is really ugly but I guess that's not our choice. :/ If QEMU ever implements APX emulation it will have NC/NDD/NF though... Paolo > If we default to setting this NCI_NDD_NF bit for APX, then in the future > when we run into other vendors that don't support this feature, we'll not > only have to make it optional again, but we'll also need to do fixes > similar to the ARCH_CAPABILITIES situation - checking vendors, fixing > compatibility issues, and all that stuff. > > Therefore, compared to default setting to constant, I think the optional > NCI_NDD_NF now not only aligns with arch spec but also prevents future > compatibility issues. :) > > Thanks, > Zhao > >
