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.
If vCPU runs in guest-mode and L1 don't intercept #GP, forward it
directly to L2. Otherwise, emulate instruction which caused #GP through
emulator.
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: Liran Alon <liran.alon@xxxxxxxxxx>
Reviewed-by: Nikita Leshenko <nikita.leshchenko@xxxxxxxxxx>
Reviewed-by: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>
Signed-off-by: Krish Sadhukhan <krish.sadhukhan@xxxxxxxxxx>
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>
---
arch/x86/kvm/vmx.c | 28 +++++++++++++++++++++++++++-
1 file changed, 27 insertions(+), 1 deletion(-)
diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
index 8eba631c4dbd..08110f39e657 100644
--- a/arch/x86/kvm/vmx.c
+++ b/arch/x86/kvm/vmx.c
@@ -1063,6 +1063,11 @@ 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))
@@ -1905,8 +1910,17 @@ static void update_exception_bitmap(struct kvm_vcpu *vcpu)
*/
if (is_guest_mode(vcpu))
eb |= get_vmcs12(vcpu)->exception_bitmap;
- else
+ else {
eb |= 1u << UD_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);
+ }
vmcs_write32(EXCEPTION_BITMAP, eb);
}
@@ -5930,6 +5944,18 @@ 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);
+ WARN_ON_ONCE(is_guest_mode(vcpu));
+ 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.
--
1.9.1
