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[PATCH v7 3/9] i386: hardcode supported eVMCS version to '1'
From: |
Vitaly Kuznetsov |
Subject: |
[PATCH v7 3/9] i386: hardcode supported eVMCS version to '1' |
Date: |
Thu, 3 Jun 2021 13:48:29 +0200 |
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@redhat.com>
---
docs/hyperv.txt | 2 +-
target/i386/kvm/kvm.c | 16 +++++++++++-----
2 files changed, 12 insertions(+), 6 deletions(-)
diff --git a/docs/hyperv.txt b/docs/hyperv.txt
index a51953daa833..000638a2fd38 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 c676ee8b38a7..d57eede5dc81 100644
--- a/target/i386/kvm/kvm.c
+++ b/target/i386/kvm/kvm.c
@@ -1490,13 +1490,19 @@ static int hyperv_init_vcpu(X86CPU *cpu)
ret = kvm_vcpu_enable_cap(cs, KVM_CAP_HYPERV_ENLIGHTENED_VMCS, 0,
(uintptr_t)&evmcs_version);
- if (ret < 0) {
- fprintf(stderr, "Hyper-V %s is not supported by kernel\n",
- kvm_hyperv_properties[HYPERV_FEAT_EVMCS].desc);
+ /*
+ * 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 || (uint8_t)evmcs_version > 1) {
+ error_report("Hyper-V %s verson 1 is not supported by kernel",
+ kvm_hyperv_properties[HYPERV_FEAT_EVMCS].desc);
return ret;
}
-
- cpu->hyperv_nested[0] = evmcs_version;
+ cpu->hyperv_nested[0] = (1 << 8) | 1;
}
return 0;
--
2.31.1
[PATCH v7 2/9] i386: clarify 'hv-passthrough' behavior, Vitaly Kuznetsov, 2021/06/03
[PATCH v7 4/9] i386: make hyperv_expand_features() return bool, Vitaly Kuznetsov, 2021/06/03
[PATCH v7 5/9] i386: expand Hyper-V features during CPU feature expansion time, Vitaly Kuznetsov, 2021/06/03