[PATCH v2 0/3] target/i386: allow using named CPU modeles with user mode emulation

[Paolo Bonzini]

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.

Other CPU models have warnings for the ARCH_CAPABILITIES MSR; hide
them as well in a similar manner.

Based-on: <20230623131711.96775-1-pbonzini@redhat.com>

Paolo Bonzini (3):
  target/i386: ignore ARCH_CAPABILITIES features in user mode emulation
  target/i386: ignore CPL0-specific features in user mode emulation
  target/i386: emulate 64-bit ring 0 for linux-user if LM feature is set

 linux-user/i386/cpu_loop.c  |  57 ++++++++++----------
 target/i386/cpu.c           | 103 +++++++++++++++++++++++++++++++++---
 target/i386/tcg/translate.c |   6 ++-
 3 files changed, 126 insertions(+), 40 deletions(-)

-- 
2.41.0