vmx: inherit default capability bits from the hypervisor

There have been some observed initialisation failures on new hypervisors
/ hardware, caused by us not recognising a new hypervisor feature.
Previously the code would print an error and exit if it encountered an
unknown feature.

However the hypervisor is able to provide a safe default, so we should
use that instead. Setting the features we want is a VMCS write and
querying the default fields is a VMCS read.

Therefore this patch

- moves the capability probing into the vCPU setup where a VMCS read is possible
- initialises the feature bits with a VMCS read (previously these were all 0)
- removes the failure case when we encounter an unknown feature bit (since the default will be safe)

Signed-off-by: David Scott <dave@recoil.org>

Author: djs55

src/lib/vmm/intel/vmx.c

@@ -596,6 +596,7 @@ vmx_vcpu_init(void *arg, int vcpuid) {
 	vmx_msr_guest_init(vmx, vcpuid);
 
 	/* Check support for primary processor-based VM-execution controls */
+	procbased_ctls = (uint32_t) vmcs_read(vcpuid, HV_VMX_CAP_PROCBASED);
 	error = vmx_set_ctlreg(HV_VMX_CAP_PROCBASED,
 			       PROCBASED_CTLS_ONE_SETTING,
 			       PROCBASED_CTLS_ZERO_SETTING, &procbased_ctls);
@@ -609,6 +610,7 @@ vmx_vcpu_init(void *arg, int vcpuid) {
 	procbased_ctls &= ~PROCBASED_CTLS_WINDOW_SETTING;
 
 	/* Check support for secondary processor-based VM-execution controls */
+	procbased_ctls2 = (uint32_t) vmcs_read(vcpuid, HV_VMX_CAP_PROCBASED2);
 	error = vmx_set_ctlreg(HV_VMX_CAP_PROCBASED2,
 			       PROCBASED_CTLS2_ONE_SETTING,
 			       PROCBASED_CTLS2_ZERO_SETTING, &procbased_ctls2);
@@ -619,6 +621,7 @@ vmx_vcpu_init(void *arg, int vcpuid) {
 	}
 
 	/* Check support for pin-based VM-execution controls */
+	pinbased_ctls = (uint32_t) vmcs_read(vcpuid, HV_VMX_CAP_PINBASED);
 	error = vmx_set_ctlreg(HV_VMX_CAP_PINBASED,
 			       PINBASED_CTLS_ONE_SETTING,
 			       PINBASED_CTLS_ZERO_SETTING, &pinbased_ctls);
@@ -629,6 +632,7 @@ vmx_vcpu_init(void *arg, int vcpuid) {
 	}
 
 	/* Check support for VM-exit controls */
+	exit_ctls = (uint32_t) vmcs_read(vcpuid, HV_VMX_CAP_EXIT);
 	error = vmx_set_ctlreg(HV_VMX_CAP_EXIT,
 			       VM_EXIT_CTLS_ONE_SETTING,
 			       VM_EXIT_CTLS_ZERO_SETTING,
@@ -640,6 +644,7 @@ vmx_vcpu_init(void *arg, int vcpuid) {
 	}
 
 	/* Check support for VM-entry controls */
+	entry_ctls = (uint32_t) vmcs_read(vcpuid, HV_VMX_CAP_ENTRY);
 	error = vmx_set_ctlreg(HV_VMX_CAP_ENTRY,
 	    VM_ENTRY_CTLS_ONE_SETTING, VM_ENTRY_CTLS_ZERO_SETTING,
 	    &entry_ctls);

src/lib/vmm/intel/vmx_msr.c

@@ -96,17 +96,17 @@ int vmx_set_ctlreg(hv_vmx_capability_t cap_field, uint32_t ones_mask,
 			}
 			*retval |= 1 << i;
 		} else {
-			/* don't care */
+			/* Hypervisor doesn't care */
 			if (zeros_mask & (1 << i)){
 				*retval &= ~(1 << i);
 			} else if (ones_mask & (1 << i)) {
 				*retval |= 1 << i;
 			} else {
-				/* XXX: don't allow unspecified don't cares */
+				/* We don't care either: inherit the system default */
 				fprintf(stderr,
 					"vmx_set_ctlreg: cap_field: %d bit: %d unspecified "
-					"don't care\n", cap_field, i);
-				return (EINVAL);
+					"don't care: bit is %d\n", cap_field, i,
+					(*retval & (1 << i))?1:0);
 			}
 		}
 	}