From ae1b11511be8c6ea7ac3b6dc46e106bb19829b0f Mon Sep 17 00:00:00 2001 From: Paolo Bonzini Date: Thu, 9 Oct 2025 16:49:59 +0200 Subject: [PATCH 3/4] target/i386: add compatibility property for arch_capabilities RH-Author: Paolo Bonzini RH-MergeRequest: 411: fix x86-64 migration regression in QEMU 10.1 RH-Jira: RHEL-120253 RH-Acked-by: Miroslav Rezanina RH-Commit: [1/2] 6bfa7c38398623ac7c3392c0ad17312e6f641f4d (bonzini/qemu-kvm-centos) JIRA: https://issues.redhat.com/browse/RHEL-120253 Prior to v10.1, if requested by user, arch-capabilities is always on despite the fact that CPUID advertises it to be off/unvailable. This causes a migration issue for VMs that are run on a machine without arch-capabilities and expect this feature to be present on the destination host with QEMU 10.1. Add a compatibility property to restore the legacy behavior for all machines with version prior to 10.1. To preserve the functionality (added by 10.1) of turning off ARCH_CAPABILITIES where Windows does not like it, use directly the guest CPU vendor: x86_cpu_get_supported_feature_word is not KVM-specific and therefore should not necessarily use the host CPUID. Co-authored-by: Hector Cao Signed-off-by: Hector Cao Fixes: d3a24134e37 ("target/i386: do not expose ARCH_CAPABILITIES on AMD CPU", 2025-07-17) Signed-off-by: Paolo Bonzini (cherry picked from commit e9efa4a77168ac2816bf9471f878252ce6224710) Signed-off-by: Paolo Bonzini --- hw/i386/pc.c | 2 ++ target/i386/cpu.c | 17 +++++++++++++++++ target/i386/cpu.h | 6 ++++++ target/i386/kvm/kvm.c | 6 +----- 4 files changed, 26 insertions(+), 5 deletions(-) diff --git a/hw/i386/pc.c b/hw/i386/pc.c index 439abe8f46..625a89d097 100644 --- a/hw/i386/pc.c +++ b/hw/i386/pc.c @@ -84,6 +84,7 @@ GlobalProperty pc_compat_10_0[] = { { TYPE_X86_CPU, "x-consistent-cache", "false" }, { TYPE_X86_CPU, "x-vendor-cpuid-only-v2", "false" }, + { TYPE_X86_CPU, "x-arch-cap-always-on", "true" }, }; const size_t pc_compat_10_0_len = G_N_ELEMENTS(pc_compat_10_0); @@ -299,6 +300,7 @@ GlobalProperty pc_rhel_10_2_compat[] = { /* pc_rhel_10_2_compat from pc_compat_10_0 */ { TYPE_X86_CPU, "x-consistent-cache", "false" }, { TYPE_X86_CPU, "x-vendor-cpuid-only-v2", "false" }, + { TYPE_X86_CPU, "x-arch-cap-always-on", "true" }, }; const size_t pc_rhel_10_2_compat_len = G_N_ELEMENTS(pc_compat_10_0); diff --git a/target/i386/cpu.c b/target/i386/cpu.c index 9c756a05f2..de288dc5ac 100644 --- a/target/i386/cpu.c +++ b/target/i386/cpu.c @@ -7559,6 +7559,20 @@ uint64_t x86_cpu_get_supported_feature_word(X86CPU *cpu, FeatureWord w) #endif break; + case FEAT_7_0_EDX: + /* + * Windows does not like ARCH_CAPABILITIES on AMD machines at all. + * Do not show the fake ARCH_CAPABILITIES MSR that KVM sets up, + * except if needed for migration. + * + * When arch_cap_always_on is removed, this tweak can move to + * kvm_arch_get_supported_cpuid. + */ + if (cpu && IS_AMD_CPU(&cpu->env) && !cpu->arch_cap_always_on) { + unavail = CPUID_7_0_EDX_ARCH_CAPABILITIES; + } + break; + default: break; } @@ -10024,6 +10038,9 @@ static const Property x86_cpu_properties[] = { true), DEFINE_PROP_BOOL("x-l1-cache-per-thread", X86CPU, l1_cache_per_core, true), DEFINE_PROP_BOOL("x-force-cpuid-0x1f", X86CPU, force_cpuid_0x1f, false), + + DEFINE_PROP_BOOL("x-arch-cap-always-on", X86CPU, + arch_cap_always_on, false), }; #ifndef CONFIG_USER_ONLY diff --git a/target/i386/cpu.h b/target/i386/cpu.h index f977fc49a7..b966bc997c 100644 --- a/target/i386/cpu.h +++ b/target/i386/cpu.h @@ -2314,6 +2314,12 @@ struct ArchCPU { /* Forcefully disable KVM PV features not exposed in guest CPUIDs */ bool kvm_pv_enforce_cpuid; + /* + * Expose arch-capabilities unconditionally even on AMD models, for backwards + * compatibility with QEMU <10.1. + */ + bool arch_cap_always_on; + /* Number of physical address bits supported */ uint32_t phys_bits; diff --git a/target/i386/kvm/kvm.c b/target/i386/kvm/kvm.c index 0eb39d22d6..baa2f80beb 100644 --- a/target/i386/kvm/kvm.c +++ b/target/i386/kvm/kvm.c @@ -503,12 +503,8 @@ uint32_t kvm_arch_get_supported_cpuid(KVMState *s, uint32_t function, * Linux v4.17-v4.20 incorrectly return ARCH_CAPABILITIES on SVM hosts. * We can detect the bug by checking if MSR_IA32_ARCH_CAPABILITIES is * returned by KVM_GET_MSR_INDEX_LIST. - * - * But also, because Windows does not like ARCH_CAPABILITIES on AMD - * mcahines at all, do not show the fake ARCH_CAPABILITIES MSR that - * KVM sets up. */ - if (!has_msr_arch_capabs || !(edx & CPUID_7_0_EDX_ARCH_CAPABILITIES)) { + if (!has_msr_arch_capabs) { ret &= ~CPUID_7_0_EDX_ARCH_CAPABILITIES; } } else if (function == 7 && index == 1 && reg == R_EAX) { -- 2.47.3