[PATCH v2 2/2] KVM: VMX: untangle VMXON revision_id setting when using eVMCS

Vitaly Kuznetsov
2020-03-05T18:37:45Z

As stated in alloc_vmxon_regions(), VMXON region needs to be tagged with
revision id from MSR_IA32_VMX_BASIC even in case of eVMCS. The logic to
do so is not very straightforward: first, we set
hdr.revision_id = KVM_EVMCS_VERSION in alloc_vmcs_cpu() just to reset it
back to vmcs_config.revision_id in alloc_vmxon_regions(). Simplify this by
introducing 'enum vmcs_type' parameter to alloc_vmcs_cpu().

No functional change intended.

Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
---
arch/x86/kvm/vmx/vmx.c | 32 ++++++++++++++------------------
arch/x86/kvm/vmx/vmx.h | 12 +++++++++---
2 files changed, 23 insertions(+), 21 deletions(-)

diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index dab19e4e5f2b..697be8823576 100644
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -2554,7 +2554,7 @@ static __init int setup_vmcs_config(struct vmcs_config *vmcs_conf,
return 0;
}

-struct vmcs *alloc_vmcs_cpu(bool shadow, int cpu, gfp_t flags)
+struct vmcs *alloc_vmcs_cpu(enum vmcs_type type, int cpu, gfp_t flags)
{
int node = cpu_to_node(cpu);
struct page *pages;
@@ -2566,13 +2566,21 @@ struct vmcs *alloc_vmcs_cpu(bool shadow, int cpu, gfp_t flags)
vmcs = page_address(pages);
memset(vmcs, 0, vmcs_config.size);

- /* KVM supports Enlightened VMCS v1 only */
- if (static_branch_unlikely(&enable_evmcs))
+ /*
+ * When eVMCS is enabled, vmcs->revision_id needs to be set to the
+ * supported eVMCS version (KVM_EVMCS_VERSION) instead of revision_id
+ * reported by MSR_IA32_VMX_BASIC.
+ *
+ * However, even though not explicitly documented by TLFS, VMXArea
+ * passed as VMXON argument should still be marked with revision_id
+ * reported by physical CPU.
+ */
+ if (type != VMXON_REGION && static_branch_unlikely(&enable_evmcs))
vmcs->hdr.revision_id = KVM_EVMCS_VERSION;
else
vmcs->hdr.revision_id = vmcs_config.revision_id;

- if (shadow)
+ if (type == SHADOW_VMCS_REGION)
vmcs->hdr.shadow_vmcs = 1;
return vmcs;
}
@@ -2652,25 +2660,13 @@ static __init int alloc_vmxon_regions(void)
for_each_possible_cpu(cpu) {
struct vmcs *vmcs;

- vmcs = alloc_vmcs_cpu(false, cpu, GFP_KERNEL);
+ /* The VMXON region is really just a special type of VMCS. */
+ vmcs = alloc_vmcs_cpu(VMXON_REGION, cpu, GFP_KERNEL);
if (!vmcs) {
free_vmxon_regions();
return -ENOMEM;
}

- /*
- * When eVMCS is enabled, alloc_vmcs_cpu() sets
- * vmcs->revision_id to KVM_EVMCS_VERSION instead of
- * revision_id reported by MSR_IA32_VMX_BASIC.
- *
- * However, even though not explicitly documented by
- * TLFS, VMXArea passed as VMXON argument should
- * still be marked with revision_id reported by
- * physical CPU.
- */
- if (static_branch_unlikely(&enable_evmcs))
- vmcs->hdr.revision_id = vmcs_config.revision_id;
-
per_cpu(vmxarea, cpu) = vmcs;
}
return 0;
diff --git a/arch/x86/kvm/vmx/vmx.h b/arch/x86/kvm/vmx/vmx.h
index e64da06c7009..4c327030bb9c 100644
--- a/arch/x86/kvm/vmx/vmx.h
+++ b/arch/x86/kvm/vmx/vmx.h
@@ -489,7 +489,13 @@ static inline struct pi_desc *vcpu_to_pi_desc(struct kvm_vcpu *vcpu)
return &(to_vmx(vcpu)->pi_desc);
}

-struct vmcs *alloc_vmcs_cpu(bool shadow, int cpu, gfp_t flags);
+enum vmcs_type {
+ VMXON_REGION,
+ VMCS_REGION,
+ SHADOW_VMCS_REGION,
+};
+
+struct vmcs *alloc_vmcs_cpu(enum vmcs_type type, int cpu, gfp_t flags);
void free_vmcs(struct vmcs *vmcs);
int alloc_loaded_vmcs(struct loaded_vmcs *loaded_vmcs);
void free_loaded_vmcs(struct loaded_vmcs *loaded_vmcs);
@@ -498,8 +504,8 @@ void loaded_vmcs_clear(struct loaded_vmcs *loaded_vmcs);

static inline struct vmcs *alloc_vmcs(bool shadow)
{
- return alloc_vmcs_cpu(shadow, raw_smp_processor_id(),
- GFP_KERNEL_ACCOUNT);
+ return alloc_vmcs_cpu(shadow ? SHADOW_VMCS_REGION : VMCS_REGION,
+ raw_smp_processor_id(), GFP_KERNEL_ACCOUNT);
}

u64 construct_eptp(struct kvm_vcpu *vcpu, unsigned long root_hpa);
--
2.24.1