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KVM: x86: Add emulation_type to not raise #UD on emulation failure 

Next commits are going introduce support for accessing VMware backdoor
ports even though guest's TSS I/O permissions bitmap doesn't allow
access. This mimic VMware hypervisor behavior.

In order to support this, next commits will change VMX/SVM to
intercept #GP which was raised by such access and handle it by calling
the x86 emulator to emulate instruction. Since commit "KVM: x86:
Always allow access to VMware backdoor I/O ports", the x86 emulator
handles access to these I/O ports by not checking these ports against
the TSS I/O permission bitmap.

However, there could be cases that CPU rasies a #GP on instruction
that fails to be disassembled by the x86 emulator (Because of
incomplete implementation for example).

In those cases, we would like the #GP intercept to just forward #GP
as-is to guest as if there was no intercept to begin with.
However, current emulator code always queues #UD exception in case
emulator fails (including disassembly failures) which is not what is
wanted in this flow.

This commit addresses this issue by adding a new emulation_type flag
that will allow the #GP intercept handler to specify that it wishes
to be aware when instruction emulation fails and doesn't want #UD
exception to be queued.

Signed-off-by: Liran Alon <liran.alon@oracle.com>
Reviewed-by: Nikita Leshenko <nikita.leshchenko@oracle.com>
Reviewed-by: Radim Krčmář <rkrcmar@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
This commit is contained in:
Liran Alon 2018-03-12 13:12:49 +02:00 committed by Paolo Bonzini
parent 9a29d449e3
commit e236617120
2 changed files with 9 additions and 3 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

1
arch/x86/include/asm/kvm_host.h
View File

@ -1193,6 +1193,7 @@ enum emulation_result {
#define EMULTYPE_SKIP (1 << 2)
#define EMULTYPE_RETRY (1 << 3)
#define EMULTYPE_NO_REEXECUTE (1 << 4)
#define EMULTYPE_NO_UD_ON_FAIL (1 << 5)
int x86_emulate_instruction(struct kvm_vcpu *vcpu, unsigned long cr2,
int emulation_type, void *insn, int insn_len);

11
arch/x86/kvm/x86.c
View File

@ -5670,18 +5670,23 @@ int kvm_inject_realmode_interrupt(struct kvm_vcpu *vcpu, int irq, int inc_eip)
}
EXPORT_SYMBOL_GPL(kvm_inject_realmode_interrupt);
static int handle_emulation_failure(struct kvm_vcpu *vcpu)
static int handle_emulation_failure(struct kvm_vcpu *vcpu, int emulation_type)
{
int r = EMULATE_DONE;
++vcpu->stat.insn_emulation_fail;
trace_kvm_emulate_insn_failed(vcpu);
if (emulation_type & EMULTYPE_NO_UD_ON_FAIL)
return EMULATE_FAIL;
if (!is_guest_mode(vcpu) && kvm_x86_ops->get_cpl(vcpu) == 0) {
vcpu->run->exit_reason = KVM_EXIT_INTERNAL_ERROR;
vcpu->run->internal.suberror = KVM_INTERNAL_ERROR_EMULATION;
vcpu->run->internal.ndata = 0;
r = EMULATE_USER_EXIT;
}
kvm_queue_exception(vcpu, UD_VECTOR);
return r;
@ -5977,7 +5982,7 @@ int x86_emulate_instruction(struct kvm_vcpu *vcpu,
return EMULATE_DONE;
if (emulation_type & EMULTYPE_SKIP)
return EMULATE_FAIL;
return handle_emulation_failure(vcpu);
return handle_emulation_failure(vcpu, emulation_type);
}
}
@ -6012,7 +6017,7 @@ int x86_emulate_instruction(struct kvm_vcpu *vcpu,
emulation_type))
return EMULATE_DONE;
return handle_emulation_failure(vcpu);
return handle_emulation_failure(vcpu, emulation_type);
}
if (ctxt->have_exception) {