Add support for "VMWRITE to any supported field in the VMCS" and
enable this feature by default in L1's IA32_VMX_MISC MSR. If userspace
clears the VMX capability bit, the old behavior will be restored.
Note that this feature is a prerequisite for kvm in L1 to use VMCS
shadowing, once that feature is available.
Signed-off-by: Jim Mattson <jmattson@xxxxxxxxxx>
---
arch/x86/kvm/vmx.c | 69 ++++++++++++++++++++++++++++++++++++++++------
1 file changed, 60 insertions(+), 9 deletions(-)
diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
index 5ea57442fef9..8a87caf452a3 100644
--- a/arch/x86/kvm/vmx.c
+++ b/arch/x86/kvm/vmx.c
@@ -1694,6 +1694,17 @@ static inline unsigned nested_cpu_vmx_misc_cr3_count(struct kvm_vcpu *vcpu)
return vmx_misc_cr3_count(to_vmx(vcpu)->nested.msrs.misc_low);
}
+/*
+ * Do the virtual VMX capability MSRs specify that L1 can use VMWRITE
+ * to modify any valid field of the VMCS, or are the VM-exit
+ * information fields read-only?
+ */
+static inline bool nested_cpu_has_vmwrite_any_field(struct kvm_vcpu *vcpu)
+{
+ return to_vmx(vcpu)->nested.msrs.misc_low &
+ MSR_IA32_VMX_MISC_VMWRITE_SHADOW_RO_FIELDS;
+}
+
static inline bool nested_cpu_has(struct vmcs12 *vmcs12, u32 bit)
{
return vmcs12->cpu_based_vm_exec_control & bit;
@@ -3311,6 +3322,7 @@ static void nested_vmx_setup_ctls_msrs(struct nested_vmx_msrs *msrs, bool apicv)
msrs->misc_high);
msrs->misc_low &= VMX_MISC_SAVE_EFER_LMA;
msrs->misc_low |=
+ MSR_IA32_VMX_MISC_VMWRITE_SHADOW_RO_FIELDS |
VMX_MISC_EMULATED_PREEMPTION_TIMER_RATE |
VMX_MISC_ACTIVITY_HLT;
msrs->misc_high = 0;
@@ -3484,6 +3496,15 @@ static int vmx_restore_vmx_misc(struct vcpu_vmx *vmx, u64 data)
vmx->nested.msrs.misc_low = data;
vmx->nested.msrs.misc_high = data >> 32;
+
+ /*
+ * If L1 has read-only VM-exit information fields, use the
+ * less permissive vmx_vmwrite_bitmap to specify write
+ * permissions for the shadow VMCS.
+ */
+ if (enable_shadow_vmcs && !nested_cpu_has_vmwrite_any_field(&vmx->vcpu))
+ vmcs_write64(VMWRITE_BITMAP, __pa(vmx_vmwrite_bitmap));
+
return 0;
}
@@ -6154,8 +6175,14 @@ static void vmx_vcpu_setup(struct vcpu_vmx *vmx)
int i;
if (enable_shadow_vmcs) {
+ /*
+ * At vCPU creation, "VMWRITE to any supported field
+ * in the VMCS" is supported, so use the more
+ * permissive vmx_vmread_bitmap to specify both read
+ * and write permissions for the shadow VMCS.
+ */
vmcs_write64(VMREAD_BITMAP, __pa(vmx_vmread_bitmap));
- vmcs_write64(VMWRITE_BITMAP, __pa(vmx_vmwrite_bitmap));
+ vmcs_write64(VMWRITE_BITMAP, __pa(vmx_vmread_bitmap));
}
if (cpu_has_vmx_msr_bitmap())
vmcs_write64(MSR_BITMAP, __pa(vmx->vmcs01.msr_bitmap));
@@ -8136,23 +8163,42 @@ static inline int vmcs12_write_any(struct kvm_vcpu *vcpu,
}
+/*
+ * Copy the writable VMCS shadow fields back to the VMCS12, in case
+ * they have been modified by the L1 guest. Note that the "read-only"
+ * VM-exit information fields are actually writable if the vCPU is
+ * configured to support "VMWRITE to any supported field in the VMCS."
+ */
static void copy_shadow_to_vmcs12(struct vcpu_vmx *vmx)
{
- int i;
+ const u16 *fields[] = {
+ shadow_read_write_fields,
+ shadow_read_only_fields
+ };
+ const int max_fields[] = {
+ max_shadow_read_write_fields,
+ max_shadow_read_only_fields
+ };
+ int i, q;
unsigned long field;
u64 field_value;
struct vmcs *shadow_vmcs = vmx->vmcs01.shadow_vmcs;
- const u16 *fields = shadow_read_write_fields;
- const int num_fields = max_shadow_read_write_fields;
preempt_disable();
vmcs_load(shadow_vmcs);
- for (i = 0; i < num_fields; i++) {
- field = fields[i];
- field_value = __vmcs_readl(field);
- vmcs12_write_any(&vmx->vcpu, field, field_value);
+ for (q = 0; q < ARRAY_SIZE(fields); q++) {
+ for (i = 0; i < max_fields[q]; i++) {
+ field = fields[q][i];
+ field_value = __vmcs_readl(field);
+ vmcs12_write_any(&vmx->vcpu, field, field_value);
+ }
+ /*
+ * Skip the VM-exit information fields if they are read-only.
+ */
+ if (!nested_cpu_has_vmwrite_any_field(&vmx->vcpu))
+ break;
}
vmcs_clear(shadow_vmcs);
@@ -8286,7 +8332,12 @@ static int handle_vmwrite(struct kvm_vcpu *vcpu)
field = kvm_register_readl(vcpu, (((vmx_instruction_info) >> 28) & 0xf));
- if (vmcs_field_readonly(field)) {
+ /*
+ * If the vCPU supports "VMWRITE to any supported field in the
+ * VMCS," then the "read-only" fields are actually read/write.
+ */
+ if (vmcs_field_readonly(field) &&
+ !nested_cpu_has_vmwrite_any_field(vcpu)) {
nested_vmx_failValid(vcpu,
VMXERR_VMWRITE_READ_ONLY_VMCS_COMPONENT);
return kvm_skip_emulated_instruction(vcpu);
