On Mon, Jun 26, 2023 at 10:33:14AM +0200, Paolo Bonzini wrote: > When running qemu-i386 even with -cpu Nehalem (aka x86_64-v2), it raises the > warning > > TCG doesn't support requested feature: CPUID.80000001H:EDX.lm [bit 29] > > Likewise using qemu-x86_64 with -cpu Haswell, it raises warnings for > > TCG doesn't support requested feature: CPUID.01H:ECX.pcid [bit 17] > TCG doesn't support requested feature: CPUID.01H:ECX.x2apic [bit 21] > TCG doesn't support requested feature: CPUID.01H:ECX.tsc-deadline [bit 24] > TCG doesn't support requested feature: CPUID.07H:EBX.invpcid [bit 10] > > Even though x86_64-v3 is the level that qemu-user is supposed to provide.
> These are two related problems: > > - for Haswell, the 4 missing features are only relevant to code running > in kernel mode; we can ignore them and mark them as supported even > though they are not. The supported features are only used to print > the warnings > > - for qemu-i386, the issue is that this emulator is restricted to running > programs on a 32-bit processor, even though it is actually emulating > programs that use the 32-bit kernel ABI on any processor. The behavior > the processor in compatibility (32-bit CS, EFER.LMA=1) mode is mostly > the same as when EFER.LMA=0 and the little code that is needed to handle > 64-bit ring-0 is even present in the qemu-i386 binary, just hidden > behind checks for HF_LMA_MASK. So, LM can also be treated as a feature > that is only relevant in kernel mode; not entirely, so this cannot yet > be extended to bsd-user, but the required changes are minimal. IMHO in this case we should hard block all named CPUs with 'lm' set from qemu-i386. It only makes sense to use named CPU models that were actually from the 32-bit era with qemu-i386. If someone wants Nehalem then they should be using qemu-x86_64. If someone wants qemu-i386 then they should be using an older named CPU model predating 'lm'. With regards, Daniel -- |: https://berrange.com -o- https://www.flickr.com/photos/dberrange :| |: https://libvirt.org -o- https://fstop138.berrange.com :| |: https://entangle-photo.org -o- https://www.instagram.com/dberrange :|
