From: Vitaly Kuznetsov <vkuznets@xxxxxxxxxx>
Currently, the only eVMCS version, supported by KVM (and described in TLFS)
is '1'. When Enlightened VMCS feature is enabled, QEMU takes the supported
eVMCS version range (from KVM_CAP_HYPERV_ENLIGHTENED_VMCS enablement) and
puts it to guest visible CPUIDs. When (and if) eVMCS ver.2 appears a
problem on migration is expected: it doesn't seem to be possible to migrate
from a host supporting eVMCS ver.2 to a host, which only support eVMCS
ver.1.
Hardcode eVMCS ver.1 as the result of 'hv-evmcs' enablement for now. Newer
eVMCS versions will have to have their own enablement options (e.g.
'hv-evmcs=2').
Signed-off-by: Vitaly Kuznetsov <vkuznets@xxxxxxxxxx>
Reviewed-by: Eduardo Habkost <ehabkost@xxxxxxxxxx>
Message-Id: <20210608120817.1325125-4-vkuznets@xxxxxxxxxx>
Signed-off-by: Eduardo Habkost <ehabkost@xxxxxxxxxx>
---
docs/hyperv.txt | 2 +-
target/i386/kvm/kvm.c | 39 +++++++++++++++++++++++++++++++++++----
2 files changed, 36 insertions(+), 5 deletions(-)
diff --git a/docs/hyperv.txt b/docs/hyperv.txt
index a51953daa83..000638a2fd3 100644
--- a/docs/hyperv.txt
+++ b/docs/hyperv.txt
@@ -170,7 +170,7 @@ Recommended: hv-frequencies
3.16. hv-evmcs
===============
The enlightenment is nested specific, it targets Hyper-V on KVM guests. When
-enabled, it provides Enlightened VMCS feature to the guest. The feature
+enabled, it provides Enlightened VMCS version 1 feature to the guest. The feature
implements paravirtualized protocol between L0 (KVM) and L1 (Hyper-V)
hypervisors making L2 exits to the hypervisor faster. The feature is Intel-only.
Note: some virtualization features (e.g. Posted Interrupts) are disabled when
diff --git a/target/i386/kvm/kvm.c b/target/i386/kvm/kvm.c
index a85035492fb..02216b70311 100644
--- a/target/i386/kvm/kvm.c
+++ b/target/i386/kvm/kvm.c
@@ -1409,6 +1409,21 @@ static int hyperv_fill_cpuids(CPUState *cs,
static Error *hv_passthrough_mig_blocker;
static Error *hv_no_nonarch_cs_mig_blocker;
+/* Checks that the exposed eVMCS version range is supported by KVM */
+static bool evmcs_version_supported(uint16_t evmcs_version,
+ uint16_t supported_evmcs_version)
+{
+ uint8_t min_version = evmcs_version & 0xff;
+ uint8_t max_version = evmcs_version >> 8;
+ uint8_t min_supported_version = supported_evmcs_version & 0xff;
+ uint8_t max_supported_version = supported_evmcs_version >> 8;
+
+ return (min_version >= min_supported_version) &&
+ (max_version <= max_supported_version);
+}
+
+#define DEFAULT_EVMCS_VERSION ((1 << 8) | 1)
+
static int hyperv_init_vcpu(X86CPU *cpu)
{
CPUState *cs = CPU(cpu);
@@ -1488,17 +1503,33 @@ static int hyperv_init_vcpu(X86CPU *cpu)
}
if (hyperv_feat_enabled(cpu, HYPERV_FEAT_EVMCS)) {
- uint16_t evmcs_version;
+ uint16_t evmcs_version = DEFAULT_EVMCS_VERSION;
+ uint16_t supported_evmcs_version;
ret = kvm_vcpu_enable_cap(cs, KVM_CAP_HYPERV_ENLIGHTENED_VMCS, 0,
- (uintptr_t)&evmcs_version);
+ (uintptr_t)&supported_evmcs_version);
+ /*
+ * KVM is required to support EVMCS ver.1. as that's what 'hv-evmcs'
+ * option sets. Note: we hardcode the maximum supported eVMCS version
+ * to '1' as well so 'hv-evmcs' feature is migratable even when (and if)
+ * ver.2 is implemented. A new option (e.g. 'hv-evmcs=2') will then have
+ * to be added.
+ */
if (ret < 0) {
- fprintf(stderr, "Hyper-V %s is not supported by kernel\n",
- kvm_hyperv_properties[HYPERV_FEAT_EVMCS].desc);
+ error_report("Hyper-V %s is not supported by kernel",
+ kvm_hyperv_properties[HYPERV_FEAT_EVMCS].desc);
return ret;
}
+ if (!evmcs_version_supported(evmcs_version, supported_evmcs_version)) {
+ error_report("eVMCS version range [%d..%d] is not supported by "
+ "kernel (supported: [%d..%d])", evmcs_version & 0xff,
+ evmcs_version >> 8, supported_evmcs_version & 0xff,
+ supported_evmcs_version >> 8);
+ return -ENOTSUP;
+ }
+
cpu->hyperv_nested[0] = evmcs_version;
}
--
2.31.1
