From ce373eb396f931d5ebdd03105a3f1950eb842cfd Mon Sep 17 00:00:00 2001 Message-ID: From: Jiri Denemark Date: Mon, 25 May 2026 14:31:07 +0200 Subject: [PATCH] qemu_capabilities: Fix domain capabilities on AMD CPUs The arch-capabilities MSR is not defined on AMD CPUs, but KVM has always been emulating them. Unfortunately, this may cause Windows to crash so QEMU (since 10.1, commit d3a24134e37d57abd3e7445842cda2717f49e96d) decided to mask the MSR by default with some additional compatibility code for older machine types. This is all mostly transparent except for probing when we run QEMU without a machine type and expand the "host" CPU model. With QEMU 10.1 and newer none of the arch-capabilities features will be shown as enabled, which may cause unexpected issues for users (such as KubeVirt) that get the list of all supported features from the host-model CPU definition in domain capabilities to select possible target nodes for migration. As a result of the change, no AMD host with new QEMU will be shown as available for incoming migration from older hosts. Since the features are supported on the host (it's possible to explicitly enable them), but they should not be enabled by default in host-model CPU, we only add the to domain capabilities when VIR_CONNECT_GET_DOMAIN_CAPABILITIES_SUPPORTED_CPU_FEATURES flag is set. Signed-off-by: Jiri Denemark Reviewed-by: Peter Krempa (cherry picked from commit 54ff2058d6f7bb2547afebbd9c65c7b4b501e372) https://redhat.atlassian.net/browse/RHEL-177364 Conflicts: tests/domaincapsdata/qemu_11.0.0-q35.x86_64+sgx-supported.xml tests/domaincapsdata/qemu_11.0.0-q35.x86_64-supported.xml - QEMU 11.0 data do not exist downstream Signed-off-by: Jiri Denemark --- src/qemu/qemu_capabilities.c | 24 +++++++++++++++++++ src/qemu/qemu_driver.c | 3 ++- .../qemu_10.1.0-q35.x86_64-supported.xml | 7 ++++++ .../qemu_10.2.0-q35.x86_64-supported.xml | 7 ++++++ 4 files changed, 40 insertions(+), 1 deletion(-) diff --git a/src/qemu/qemu_capabilities.c b/src/qemu/qemu_capabilities.c index 555723cafb..f06f376dd7 100644 --- a/src/qemu/qemu_capabilities.c +++ b/src/qemu/qemu_capabilities.c @@ -6604,6 +6604,7 @@ virQEMUCapsFillDomainCPUHostModel(virQEMUCaps *qemuCaps, { virQEMUCapsHostCPUType cpuType; virCPUDef *cpu; + virArch arch = domCaps->arch; if (flags & VIR_CONNECT_GET_DOMAIN_CAPABILITIES_EXPAND_CPU_FEATURES) cpuType = VIR_QEMU_CAPS_HOST_CPU_EXPANDED; @@ -6620,6 +6621,29 @@ virQEMUCapsFillDomainCPUHostModel(virQEMUCaps *qemuCaps, cpu, VIR_CPU_FEATURE_DISABLE); } + if (flags & VIR_CONNECT_GET_DOMAIN_CAPABILITIES_SUPPORTED_CPU_FEATURES) { + uint32_t index = 0x10a; /* arch-capabilities MSR */ + uint64_t msr = 0; + + /* While the arch-capabilities MSR is not defined on AMD CPUs, KVM has + * always been emulating them. Unfortunately, this may cause some + * Windows version to crash so QEMU decided to mask the MSR by default. + * When asked for all CPU features supported on a host we need to add + * the affected features to the host-model. + */ + if (ARCH_IS_X86(arch) && + STREQ_NULLABLE(cpu->vendor, "AMD") && + virCPUCheckFeature(arch, cpu, "arch-capabilities") == 0 && + virHostCPUGetMSRFromKVM(index, &msr) == 0) { + g_autoptr(virCPUData) data = virCPUDataNew(arch); + virCPUFeaturePolicy policy = VIR_CPU_FEATURE_REQUIRE; + + virCPUx86DataAddMSR(data, index, msr); + virCPUUpdateFeatures(arch, cpu, data, policy); + virCPUDefUpdateFeature(cpu, "arch-capabilities", policy); + } + } + virCPUDefSortFeatures(cpu); domCaps->cpu.hostModel = cpu; } diff --git a/src/qemu/qemu_driver.c b/src/qemu/qemu_driver.c index 0a61f97666..dcb49a9d42 100644 --- a/src/qemu/qemu_driver.c +++ b/src/qemu/qemu_driver.c @@ -16721,7 +16721,8 @@ qemuConnectGetDomainCapabilities(virConnectPtr conn, g_autoptr(virDomainCaps) domCaps = NULL; virCheckFlags(VIR_CONNECT_GET_DOMAIN_CAPABILITIES_DISABLE_DEPRECATED_FEATURES | - VIR_CONNECT_GET_DOMAIN_CAPABILITIES_EXPAND_CPU_FEATURES, + VIR_CONNECT_GET_DOMAIN_CAPABILITIES_EXPAND_CPU_FEATURES | + VIR_CONNECT_GET_DOMAIN_CAPABILITIES_SUPPORTED_CPU_FEATURES, NULL); if (virConnectGetDomainCapabilitiesEnsureACL(conn) < 0) diff --git a/tests/domaincapsdata/qemu_10.1.0-q35.x86_64-supported.xml b/tests/domaincapsdata/qemu_10.1.0-q35.x86_64-supported.xml index 244fce575b..4ea61a6cbe 100644 --- a/tests/domaincapsdata/qemu_10.1.0-q35.x86_64-supported.xml +++ b/tests/domaincapsdata/qemu_10.1.0-q35.x86_64-supported.xml @@ -45,17 +45,24 @@ AMD + + + + + + + diff --git a/tests/domaincapsdata/qemu_10.2.0-q35.x86_64-supported.xml b/tests/domaincapsdata/qemu_10.2.0-q35.x86_64-supported.xml index 9389141012..d9c0ea6f1d 100644 --- a/tests/domaincapsdata/qemu_10.2.0-q35.x86_64-supported.xml +++ b/tests/domaincapsdata/qemu_10.2.0-q35.x86_64-supported.xml @@ -44,12 +44,19 @@ EPYC-Turin AMD + + + + + + + -- 2.54.0