[PATCH v2 06/28] KVM: nVMX: Introduce KVM_CAP_HYPERV_ENLIGHTENED_VMCS2

From: Vitaly Kuznetsov
Date: Wed Jun 29 2022 - 11:07:10 EST

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Turns out Enlightened VMCS can gain new fields without version change
and KVM_CAP_HYPERV_ENLIGHTENED_VMCS which KVM currently has cant's
handle this reliably. In particular, just updating the current definition
of eVMCSv1 with the new fields and adjusting the VMX MSR filtering will
inevitably break live migration to older KVMs. Note: enabling eVMCS and
setting VMX feature MSR can happen in any order.

Introduce a notion of KVM internal "Enlightened VMCS revision" and add
a new capability allowing to add fields to Enlightened VMCS while keeping
its version.

Signed-off-by: Vitaly Kuznetsov <vkuznets@xxxxxxxxxx>
---
Documentation/virt/kvm/api.rst | 43 ++++++++++++++++++++++++++++++++-
arch/x86/include/asm/kvm_host.h | 2 +-
arch/x86/kvm/vmx/evmcs.c | 20 ++++++++++-----
arch/x86/kvm/vmx/evmcs.h | 13 ++++++++--
arch/x86/kvm/vmx/nested.c | 10 ++++----
arch/x86/kvm/vmx/vmx.c | 2 +-
arch/x86/kvm/vmx/vmx.h | 15 ++++++------
arch/x86/kvm/x86.c | 15 +++++++++++-
include/uapi/linux/kvm.h | 3 ++-
9 files changed, 98 insertions(+), 25 deletions(-)

diff --git a/Documentation/virt/kvm/api.rst b/Documentation/virt/kvm/api.rst
index bafaeedd455c..1e55855724e5 100644
--- a/Documentation/virt/kvm/api.rst
+++ b/Documentation/virt/kvm/api.rst
@@ -4974,7 +4974,7 @@ version has the following quirks:

- HYPERV_CPUID_NESTED_FEATURES leaf and HV_X64_ENLIGHTENED_VMCS_RECOMMENDED
feature bit are only exposed when Enlightened VMCS was previously enabled
- on the corresponding vCPU (KVM_CAP_HYPERV_ENLIGHTENED_VMCS).
+ on the corresponding vCPU (KVM_CAP_HYPERV_ENLIGHTENED_VMCS2).
- HV_STIMER_DIRECT_MODE_AVAILABLE bit is only exposed with in-kernel LAPIC.
(presumes KVM_CREATE_IRQCHIP has already been called).

@@ -8223,6 +8223,47 @@ The capability has no effect if the nx_huge_pages module parameter is not set.

This capability may only be set before any vCPUs are created.

+8.39 KVM_CAP_HYPERV_ENLIGHTENED_VMCS
+------------------------------------
+
+:Capability: KVM_CAP_HYPERV_ENLIGHTENED_VMCS
+:Architectures: x86
+:Type: vcpu
+:Parameters: arg[0] is a pointer to uint16_t where the supported Enlightened
+VMCS version range will be stored by KVM.
+:Returns: 0 on success, -EINVAL when Enlightened VMCS is already enabled,
+-EFAULT when write to arg[0] fails.
+
+This capability enables Enlightened VMCS interface. Obsolete, use
+KVM_CAP_HYPERV_ENLIGHTENED_VMCS2 instead.
+
+8.40 KVM_CAP_HYPERV_ENLIGHTENED_VMCS2
+-------------------------------------
+
+:Capability: KVM_CAP_HYPERV_ENLIGHTENED_VMCS2
+:Architectures: x86
+:Type: vcpu
+:Parameters: arg[0] is the desired Enlightened VMCS revision (uint32_t). Special
+value 'U32_MAX' indicates the latest supported revision. (Optional) arg[1] is a
+pointer to 'uint16_t' where the supported Enlightened VMCS version range will be
+stored by KVM.
+:Returns: 0 on success, -ENOTTY on SVM, -EINVAL when Enlightened VMCS is already
+enabled or the requested revision is not supported, -EFAULT when write to arg[1]
+fails.
+
+This capability enables Hyper-V Enlightened VMCS interface as described in
+Hyper-V Top Level Functional Specification (TLFS). Note: when the interface is
+enabled, L1 guest doesn't necessarily have to use it, however, the exposed VMX
+features will be limited to what the particular revision of the Enlightened VMCS
+supports.
+
+Enlightened VMCS version range (optionally written to arg[1]) is encoded in the
+following way:
+ ((uint8_t)HIGHEST_SUPPORTED_VERSION << 8) | (uint8_t)LOWEST_SUPPORTED_VERSION
+
+The interface is only available on VMX. Once set, changing the supported
+Enlightened VMCS revision not supported.
+
9. Known KVM API problems
=========================

diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index de5a149d0971..4cb253cec5bb 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -1648,7 +1648,7 @@ struct kvm_x86_nested_ops {
bool (*get_nested_state_pages)(struct kvm_vcpu *vcpu);
int (*write_log_dirty)(struct kvm_vcpu *vcpu, gpa_t l2_gpa);

- int (*enable_evmcs)(struct kvm_vcpu *vcpu,
+ int (*enable_evmcs)(struct kvm_vcpu *vcpu, u32 evmcs_revision,
uint16_t *vmcs_version);
uint16_t (*get_evmcs_version)(struct kvm_vcpu *vcpu);
};
diff --git a/arch/x86/kvm/vmx/evmcs.c b/arch/x86/kvm/vmx/evmcs.c
index 8bea5dea0341..21d9f0ed4bd2 100644
--- a/arch/x86/kvm/vmx/evmcs.c
+++ b/arch/x86/kvm/vmx/evmcs.c
@@ -362,7 +362,7 @@ uint16_t nested_get_evmcs_version(struct kvm_vcpu *vcpu)
* KVM_EVMCS_VERSION.
*/
if (kvm_cpu_cap_get(X86_FEATURE_VMX) &&
- (!vcpu || to_vmx(vcpu)->nested.enlightened_vmcs_enabled))
+ (!vcpu || to_vmx(vcpu)->nested.active_evmcs_revision))
return (KVM_EVMCS_VERSION << 8) | 1;

return 0;
@@ -453,15 +453,23 @@ int nested_evmcs_check_controls(struct vmcs12 *vmcs12)
return ret;
}

-int nested_enable_evmcs(struct kvm_vcpu *vcpu,
- uint16_t *vmcs_version)
+int nested_enable_evmcs(struct kvm_vcpu *vcpu, u32 evmcs_revision, uint16_t *evmcs_version)
{
struct vcpu_vmx *vmx = to_vmx(vcpu);

- vmx->nested.enlightened_vmcs_enabled = true;
+ if (evmcs_revision > KVM_EVMCS_REVISION && evmcs_revision != U32_MAX)
+ return -EINVAL;

- if (vmcs_version)
- *vmcs_version = nested_get_evmcs_version(vcpu);
+ /* Disabling or changing active eVMCS version is not supported */
+ if (vmx->nested.active_evmcs_revision)
+ return -EINVAL;
+
+ if (evmcs_revision != U32_MAX)
+ vmx->nested.active_evmcs_revision = evmcs_revision;
+ else
+ vmx->nested.active_evmcs_revision = KVM_EVMCS_REVISION;
+
+ *evmcs_version = nested_get_evmcs_version(vcpu);

return 0;
}
diff --git a/arch/x86/kvm/vmx/evmcs.h b/arch/x86/kvm/vmx/evmcs.h
index f886a8ff0342..022a51ae81e4 100644
--- a/arch/x86/kvm/vmx/evmcs.h
+++ b/arch/x86/kvm/vmx/evmcs.h
@@ -18,8 +18,18 @@ DECLARE_STATIC_KEY_FALSE(enable_evmcs);

#define current_evmcs ((struct hv_enlightened_vmcs *)this_cpu_read(current_vmcs))

+/*
+ * Maximum supported eVMCS version as described in TLFS, gets reported to the
+ * guest.
+ */
#define KVM_EVMCS_VERSION 1

+/*
+ * Internal KVM eVMCS revision number, gets bumped when eVMCS needs to be
+ * updated but its version remain intact.
+ */
+#define KVM_EVMCS_REVISION 1
+
/*
* Enlightened VMCSv1 doesn't support these:
*
@@ -241,8 +251,7 @@ enum nested_evmptrld_status {

bool nested_enlightened_vmentry(struct kvm_vcpu *vcpu, u64 *evmcs_gpa);
uint16_t nested_get_evmcs_version(struct kvm_vcpu *vcpu);
-int nested_enable_evmcs(struct kvm_vcpu *vcpu,
- uint16_t *vmcs_version);
+int nested_enable_evmcs(struct kvm_vcpu *vcpu, u32 evmcs_revision, uint16_t *vmcs_version);
void nested_evmcs_filter_control_msr(u32 msr_index, u64 *pdata);
int nested_evmcs_check_controls(struct vmcs12 *vmcs12);

diff --git a/arch/x86/kvm/vmx/nested.c b/arch/x86/kvm/vmx/nested.c
index 4fc84f0f5875..2ff361a0285f 100644
--- a/arch/x86/kvm/vmx/nested.c
+++ b/arch/x86/kvm/vmx/nested.c
@@ -2009,7 +2009,7 @@ static enum nested_evmptrld_status nested_vmx_handle_enlightened_vmptrld(
bool evmcs_gpa_changed = false;
u64 evmcs_gpa;

- if (likely(!vmx->nested.enlightened_vmcs_enabled))
+ if (likely(!vmx->nested.active_evmcs_revision))
return EVMPTRLD_DISABLED;

if (!nested_enlightened_vmentry(vcpu, &evmcs_gpa)) {
@@ -2890,7 +2890,7 @@ static int nested_vmx_check_controls(struct kvm_vcpu *vcpu,
nested_check_vm_entry_controls(vcpu, vmcs12))
return -EINVAL;

- if (to_vmx(vcpu)->nested.enlightened_vmcs_enabled)
+ if (to_vmx(vcpu)->nested.active_evmcs_revision)
return nested_evmcs_check_controls(vmcs12);

return 0;
@@ -3172,7 +3172,7 @@ static bool nested_get_evmcs_page(struct kvm_vcpu *vcpu)
* L2 was running), map it here to make sure vmcs12 changes are
* properly reflected.
*/
- if (vmx->nested.enlightened_vmcs_enabled &&
+ if (vmx->nested.active_evmcs_revision &&
vmx->nested.hv_evmcs_vmptr == EVMPTR_MAP_PENDING) {
enum nested_evmptrld_status evmptrld_status =
nested_vmx_handle_enlightened_vmptrld(vcpu, false);
@@ -5110,7 +5110,7 @@ static int handle_vmclear(struct kvm_vcpu *vcpu)
* state. It is possible that the area will stay mapped as
* vmx->nested.hv_evmcs but this shouldn't be a problem.
*/
- if (likely(!vmx->nested.enlightened_vmcs_enabled ||
+ if (likely(!vmx->nested.active_evmcs_revision ||
!nested_enlightened_vmentry(vcpu, &evmcs_gpa))) {
if (vmptr == vmx->nested.current_vmptr)
nested_release_vmcs12(vcpu);
@@ -6399,7 +6399,7 @@ static int vmx_set_nested_state(struct kvm_vcpu *vcpu,
return -EINVAL;

if ((kvm_state->flags & KVM_STATE_NESTED_EVMCS) &&
- (!nested_vmx_allowed(vcpu) || !vmx->nested.enlightened_vmcs_enabled))
+ (!nested_vmx_allowed(vcpu) || !vmx->nested.active_evmcs_revision))
return -EINVAL;

vmx_leave_nested(vcpu);
diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index c30115b9cb33..76f83af7d901 100644
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -1857,7 +1857,7 @@ static int vmx_get_msr(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
* features out.
*/
if (!msr_info->host_initiated &&
- vmx->nested.enlightened_vmcs_enabled)
+ vmx->nested.active_evmcs_revision)
nested_evmcs_filter_control_msr(msr_info->index,
&msr_info->data);
break;
diff --git a/arch/x86/kvm/vmx/vmx.h b/arch/x86/kvm/vmx/vmx.h
index 286c88e285ea..65b3aeb00a6a 100644
--- a/arch/x86/kvm/vmx/vmx.h
+++ b/arch/x86/kvm/vmx/vmx.h
@@ -185,13 +185,6 @@ struct nested_vmx {
bool update_vmcs01_cpu_dirty_logging;
bool update_vmcs01_apicv_status;

- /*
- * Enlightened VMCS has been enabled. It does not mean that L1 has to
- * use it. However, VMX features available to L1 will be limited based
- * on what the enlightened VMCS supports.
- */
- bool enlightened_vmcs_enabled;
-
/* L2 must run next, and mustn't decide to exit to L1. */
bool nested_run_pending;

@@ -248,6 +241,14 @@ struct nested_vmx {
bool guest_mode;
} smm;

+ /*
+ * Enlightened VMCS revision enabled (1..KVM_EVMCS_REVISION) on the vCPU.
+ * When, enabled, L1 doesn't necessarily have to use eVMCS interface,
+ * however, the exposed VMX features will be limited to what the particular
+ * revision of eVMCS supports.
+ */
+ u32 active_evmcs_revision;
+
gpa_t hv_evmcs_vmptr;
struct kvm_host_map hv_evmcs_map;
struct hv_enlightened_vmcs *hv_evmcs;
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 567d13405445..52d998ad1e45 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -4444,6 +4444,7 @@ int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext)
r = kvm_x86_ops.enable_direct_tlbflush != NULL;
break;
case KVM_CAP_HYPERV_ENLIGHTENED_VMCS:
+ case KVM_CAP_HYPERV_ENLIGHTENED_VMCS2:
r = kvm_x86_ops.nested_ops->enable_evmcs != NULL;
break;
case KVM_CAP_SMALLER_MAXPHYADDR:
@@ -5421,7 +5422,8 @@ static int kvm_vcpu_ioctl_enable_cap(struct kvm_vcpu *vcpu,
case KVM_CAP_HYPERV_ENLIGHTENED_VMCS:
if (!kvm_x86_ops.nested_ops->enable_evmcs)
return -ENOTTY;
- r = kvm_x86_ops.nested_ops->enable_evmcs(vcpu, &vmcs_version);
+ /* Legacy: enable rev.1 */
+ r = kvm_x86_ops.nested_ops->enable_evmcs(vcpu, 1, &vmcs_version);
if (!r) {
user_ptr = (void __user *)(uintptr_t)cap->args[0];
if (copy_to_user(user_ptr, &vmcs_version,
@@ -5429,6 +5431,17 @@ static int kvm_vcpu_ioctl_enable_cap(struct kvm_vcpu *vcpu,
r = -EFAULT;
}
return r;
+ case KVM_CAP_HYPERV_ENLIGHTENED_VMCS2:
+ if (!kvm_x86_ops.nested_ops->enable_evmcs)
+ return -ENOTTY;
+ r = kvm_x86_ops.nested_ops->enable_evmcs(vcpu, cap->args[0], &vmcs_version);
+ if (!r && cap->args[1]) {
+ user_ptr = (void __user *)(uintptr_t)cap->args[1];
+ if (copy_to_user(user_ptr, &vmcs_version,
+ sizeof(vmcs_version)))
+ r = -EFAULT;
+ }
+ return r;
case KVM_CAP_HYPERV_DIRECT_TLBFLUSH:
if (!kvm_x86_ops.enable_direct_tlbflush)
return -ENOTTY;
diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h
index a36e78710382..ad6a2f220abc 100644
--- a/include/uapi/linux/kvm.h
+++ b/include/uapi/linux/kvm.h
@@ -1109,7 +1109,7 @@ struct kvm_ppc_resize_hpt {
#define KVM_CAP_PPC_NESTED_HV 160
#define KVM_CAP_HYPERV_SEND_IPI 161
#define KVM_CAP_COALESCED_PIO 162
-#define KVM_CAP_HYPERV_ENLIGHTENED_VMCS 163
+#define KVM_CAP_HYPERV_ENLIGHTENED_VMCS 163 /* Obsolete */
#define KVM_CAP_EXCEPTION_PAYLOAD 164
#define KVM_CAP_ARM_VM_IPA_SIZE 165
#define KVM_CAP_MANUAL_DIRTY_LOG_PROTECT 166 /* Obsolete */
@@ -1167,6 +1167,7 @@ struct kvm_ppc_resize_hpt {
#define KVM_CAP_X86_TRIPLE_FAULT_EVENT 218
#define KVM_CAP_X86_NOTIFY_VMEXIT 219
#define KVM_CAP_VM_DISABLE_NX_HUGE_PAGES 220
+#define KVM_CAP_HYPERV_ENLIGHTENED_VMCS2 221

#ifdef KVM_CAP_IRQ_ROUTING

--
2.35.3

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