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Commit 9718420e authored by Liran Alon's avatar Liran Alon Committed by Paolo Bonzini
Browse files

KVM: x86: SVM: Intercept #GP to support access to VMware backdoor ports 



If KVM enable_vmware_backdoor module parameter is set,
the commit change VMX to now intercept #GP instead of being directly
deliviered from CPU to guest.

It is done to support access to VMware Backdoor I/O ports
even if TSS I/O permission denies it.
In that case:
1. A #GP will be raised and intercepted.
2. #GP intercept handler will simulate I/O port access instruction.
3. I/O port access instruction simulation will allow access to VMware
backdoor ports specifically even if TSS I/O permission bitmap denies it.

Note that the above change introduce slight performance hit as now #GPs
are now not deliviered directly from CPU to guest but instead
cause #VMExit and instruction emulation.
However, this behavior is introduced only when enable_vmware_backdoor
KVM module parameter is set.

Signed-off-by: default avatarLiran Alon <liran.alon@oracle.com>
Reviewed-by: default avatarNikita Leshenko <nikita.leshchenko@oracle.com>
Reviewed-by: default avatarKonrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Reviewed-by: default avatarRadim Krčmář <rkrcmar@redhat.com>
Signed-off-by: default avatarPaolo Bonzini <pbonzini@redhat.com>
parent 9e869480

arch/x86/kvm/svm.c

+26 −0
Original line number Diff line number Diff line
@@ -1364,6 +1364,14 @@ static void init_vmcb(struct vcpu_svm *svm) 
	set_exception_intercept(svm, MC_VECTOR);

	set_exception_intercept(svm, AC_VECTOR);

	set_exception_intercept(svm, DB_VECTOR);

	/*

	 * Guest access to VMware backdoor ports could legitimately

	 * trigger #GP because of TSS I/O permission bitmap.

	 * We intercept those #GP and allow access to them anyway

	 * as VMware does.

	 */

	if (enable_vmware_backdoor)

		set_exception_intercept(svm, GP_VECTOR);



	set_intercept(svm, INTERCEPT_INTR);

	set_intercept(svm, INTERCEPT_NMI);
@@ -2552,6 +2560,23 @@ static int ac_interception(struct vcpu_svm *svm) 
	return 1;

}



static int gp_interception(struct vcpu_svm *svm)

{

	struct kvm_vcpu *vcpu = &svm->vcpu;

	u32 error_code = svm->vmcb->control.exit_info_1;

	int er;



	WARN_ON_ONCE(!enable_vmware_backdoor);



	er = emulate_instruction(vcpu,

		EMULTYPE_VMWARE | EMULTYPE_NO_UD_ON_FAIL);

	if (er == EMULATE_USER_EXIT)

		return 0;

	else if (er != EMULATE_DONE)

		kvm_queue_exception_e(vcpu, GP_VECTOR, error_code);

	return 1;

}



static bool is_erratum_383(void)

{

	int err, i;
@@ -4551,6 +4576,7 @@ static int (*const svm_exit_handlers[])(struct vcpu_svm *svm) = { 
	[SVM_EXIT_EXCP_BASE + PF_VECTOR]	= pf_interception,

	[SVM_EXIT_EXCP_BASE + MC_VECTOR]	= mc_interception,

	[SVM_EXIT_EXCP_BASE + AC_VECTOR]	= ac_interception,

	[SVM_EXIT_EXCP_BASE + GP_VECTOR]	= gp_interception,

	[SVM_EXIT_INTR]				= intr_interception,

	[SVM_EXIT_NMI]				= nmi_interception,

	[SVM_EXIT_SMI]				= nop_on_interception,