On 06/11/17 15:50, Paolo Bonzini wrote:
On 06/11/2017 14:25, Liran Alon wrote:
What is the caller of x86_emulate_instruction that you are interested
in? #UD is not affected, because emulation_type has EMULTYPE_TRAP_UD
set and therefore x86_emulate_instruction exits before invoking
handle_emulation_failure.
I think this patch is still correct from a number of reasons:
1) If I understand the code correctly, semantically it doesn't make
sense to fill kvm_run struct without exiting to user-mode. Therefore, if
emulator filled kvm_run, it makes sense that it needs to return
EMULATE_USER_EXIT.
2) EMULTYPE_TRAP_UD only causes the emulator to return EMULATE_FAIL in
case emulation fails on instruction decoding. However, consider a case
where #UD intercept happens on a valid instruction (such as VMMCALL AMD
opcode on physical Intel CPU). In that case, instruction decoding
doesn't fail but we could still fail on instruction emulation at
x86_emulate_insn(). In this case, EMULTYPE_TRAP_UD flag is not
considered anymore and failure will reach handle_emulation_failure().
(1) is true, but (2) more or less answers my question. So
Reviewed-by: Paolo Bonzini <pbonzini@xxxxxxxxxx>
3) We have another KVM commits series (not upstream yet) that adds
intercept on #GP which calls the x86 emulator. This is done to allow
access to I/O ports even though they aren't allowed via guest's TSS I/O
permissions bitmap.
vmport?... :)
Yep. Stay tuned. :)
Paolo
