[PATCH 00/10] KVM: emulate: enable AVX moves

Paolo Bonzini
2025-11-14T00:36:40Z

Over a year ago, Keith Busch posted an RFC patch to enable VMOVDQA
and VMOVDQU instructions in the KVM emulator. The reason to do so
is that people are using QEMU to emulate fancy devices whose drivers
use those instructions with BARs that, on real hardware, would
presumably support write combining. These same people obviously
would appreciate being able to use KVM instead of emulation, hence
the request.

The original patch was not bad at all, but missed a few details:

- checking in XCR0 if AVX is enabled (which also protects against
*hosts* with AVX disabled)

- 32-bit support

- clearing the high bytes of AVX registers if VEX.L=0

- checking some invalid prefix combinations

The ugly parts are in patch 7, which has to juggle the fact that the
same instruction can decode to SSE and AVX, and we only know which are
valid after all the groups are handled.

While at it I also included a small refactoring taken out of the
APX series, by Chang S. Bae, some cleanups, and an extra MOVNTDQ
instruction.

Paolo

Chang S. Bae (1):
KVM: x86: Refactor REX prefix handling in instruction emulation

Paolo Bonzini (9):
KVM: emulate: add MOVNTDQA
KVM: emulate: move Src2Shift up one bit
KVM: emulate: improve formatting of flags table
KVM: emulate: move op_prefix to struct x86_emulate_ctxt
KVM: emulate: share common register decoding code
KVM: emulate: add get_xcr callback
KVM: emulate: add AVX support to register fetch and writeback
KVM: emulate: decode VEX prefix
KVM: emulate: enable AVX moves

arch/x86/kvm/emulate.c | 320 ++++++++++++++++++++++++++-----------
arch/x86/kvm/fpu.h | 62 +++++++
arch/x86/kvm/kvm_emulate.h | 20 ++-
arch/x86/kvm/x86.c | 9 ++
4 files changed, 311 insertions(+), 100 deletions(-)

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2.43.5