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Commit 9e869480 authored by Liran Alon's avatar Liran Alon Committed by Paolo Bonzini
Browse files

KVM: x86: VMX: 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 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 04789b66

arch/x86/kvm/vmx.c

+24 −0
Original line number Diff line number Diff line
@@ -1039,6 +1039,11 @@ static inline bool is_invalid_opcode(u32 intr_info) 
	return is_exception_n(intr_info, UD_VECTOR);

}



static inline bool is_gp_fault(u32 intr_info)

{

	return is_exception_n(intr_info, GP_VECTOR);

}



static inline bool is_external_interrupt(u32 intr_info)

{

	return (intr_info & (INTR_INFO_INTR_TYPE_MASK | INTR_INFO_VALID_MASK))
@@ -1875,6 +1880,14 @@ static void update_exception_bitmap(struct kvm_vcpu *vcpu) 


	eb = (1u << PF_VECTOR) | (1u << UD_VECTOR) | (1u << MC_VECTOR) |

	     (1u << DB_VECTOR) | (1u << AC_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)

		eb |= (1u << GP_VECTOR);

	if ((vcpu->guest_debug &

	     (KVM_GUESTDBG_ENABLE | KVM_GUESTDBG_USE_SW_BP)) ==

	    (KVM_GUESTDBG_ENABLE | KVM_GUESTDBG_USE_SW_BP))
@@ -6180,6 +6193,17 @@ static int handle_exception(struct kvm_vcpu *vcpu) 
	if (intr_info & INTR_INFO_DELIVER_CODE_MASK)

		error_code = vmcs_read32(VM_EXIT_INTR_ERROR_CODE);



	if (!vmx->rmode.vm86_active && is_gp_fault(intr_info)) {

		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;

	}



	/*

	 * The #PF with PFEC.RSVD = 1 indicates the guest is accessing

	 * MMIO, it is better to report an internal error.