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KVM: x86: Add comments to document various emulation types

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Document the intended usage of each emulation type as each exists to
handle an edge case of one kind or another and can be easily
misinterpreted at first glance.

Cc: Liran Alon <liran.alon@oracle.com>
Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
This commit is contained in:
Sean Christopherson 2019-08-27 14:40:40 -07:00 committed by Paolo Bonzini
parent 1957aa63be
commit 41577ab8bd
1 changed files with 30 additions and 0 deletions
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30
arch/x86/include/asm/kvm_host.h
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@ -1315,6 +1315,36 @@ extern u64 kvm_default_tsc_scaling_ratio;
extern u64 kvm_mce_cap_supported;
/*
* EMULTYPE_NO_DECODE - Set when re-emulating an instruction (after completing
* userspace I/O) to indicate that the emulation context
* should be resued as is, i.e. skip initialization of
* emulation context, instruction fetch and decode.
*
* EMULTYPE_TRAP_UD - Set when emulating an intercepted #UD from hardware.
* Indicates that only select instructions (tagged with
* EmulateOnUD) should be emulated (to minimize the emulator
* attack surface). See also EMULTYPE_TRAP_UD_FORCED.
*
* EMULTYPE_SKIP - Set when emulating solely to skip an instruction, i.e. to
* decode the instruction length. For use *only* by
* kvm_x86_ops->skip_emulated_instruction() implementations.
*
* EMULTYPE_ALLOW_RETRY - Set when the emulator should resume the guest to
* retry native execution under certain conditions.
*
* EMULTYPE_TRAP_UD_FORCED - Set when emulating an intercepted #UD that was
* triggered by KVM's magic "force emulation" prefix,
* which is opt in via module param (off by default).
* Bypasses EmulateOnUD restriction despite emulating
* due to an intercepted #UD (see EMULTYPE_TRAP_UD).
* Used to test the full emulator from userspace.
*
* EMULTYPE_VMWARE_GP - Set when emulating an intercepted #GP for VMware
* backdoor emulation, which is opt in via module param.
* VMware backoor emulation handles select instructions
* and reinjects the #GP for all other cases.
*/
#define EMULTYPE_NO_DECODE (1 << 0)
#define EMULTYPE_TRAP_UD (1 << 1)
#define EMULTYPE_SKIP (1 << 2)