126 lines
4.9 KiB
Diff
126 lines
4.9 KiB
Diff
From f12894cd72bfe359ed3438fad9f28cc2d282ab0b Mon Sep 17 00:00:00 2001
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From: Paolo Bonzini <pbonzini@redhat.com>
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Date: Thu, 9 Oct 2025 16:47:10 +0200
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Subject: [PATCH] target/i386: add compatibility property for arch_capabilities
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JIRA: https://issues.redhat.com/browse/RHEL-120257
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Prior to v10.1, if requested by user, arch-capabilities is always on
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despite the fact that CPUID advertises it to be off/unvailable.
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This causes a migration issue for VMs that are run on a machine
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without arch-capabilities and expect this feature to be present
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on the destination host with QEMU 10.1.
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Add a compatibility property to restore the legacy behavior for all
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machines with version prior to 10.1.
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To preserve the functionality (added by 10.1) of turning off
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ARCH_CAPABILITIES where Windows does not like it, use directly
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the guest CPU vendor: x86_cpu_get_supported_feature_word is not
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KVM-specific and therefore should not necessarily use the host
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CPUID.
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Co-authored-by: Hector Cao <hector.cao@canonical.com>
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Signed-off-by: Hector Cao <hector.cao@canonical.com>
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Fixes: d3a24134e37 ("target/i386: do not expose ARCH_CAPABILITIES on AMD CPU", 2025-07-17)
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Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
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(cherry picked from commit e9efa4a77168ac2816bf9471f878252ce6224710)
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Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
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---
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hw/i386/pc.c | 2 ++
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target/i386/cpu.c | 17 +++++++++++++++++
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target/i386/cpu.h | 6 ++++++
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target/i386/kvm/kvm.c | 6 +-----
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4 files changed, 26 insertions(+), 5 deletions(-)
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diff --git a/hw/i386/pc.c b/hw/i386/pc.c
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index 79a6105f8b..ee8c221505 100644
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--- a/hw/i386/pc.c
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+++ b/hw/i386/pc.c
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@@ -84,6 +84,7 @@
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GlobalProperty pc_compat_10_0[] = {
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{ TYPE_X86_CPU, "x-consistent-cache", "false" },
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{ TYPE_X86_CPU, "x-vendor-cpuid-only-v2", "false" },
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+ { TYPE_X86_CPU, "x-arch-cap-always-on", "true" },
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};
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const size_t pc_compat_10_0_len = G_N_ELEMENTS(pc_compat_10_0);
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@@ -299,6 +300,7 @@ GlobalProperty pc_rhel_9_8_compat[] = {
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/* pc_rhel_10_2_compat from pc_compat_10_0 */
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{ TYPE_X86_CPU, "x-consistent-cache", "false" },
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{ TYPE_X86_CPU, "x-vendor-cpuid-only-v2", "false" },
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+ { TYPE_X86_CPU, "x-arch-cap-always-on", "true" },
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/* pc_rhel_9_8_compat from pc_compat_9_1 */
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{ "ICH9-LPC", "x-smi-swsmi-timer", "off" },
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{ "ICH9-LPC", "x-smi-periodic-timer", "off" },
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diff --git a/target/i386/cpu.c b/target/i386/cpu.c
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index 2c4ddd7c63..9fb70ac344 100644
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--- a/target/i386/cpu.c
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+++ b/target/i386/cpu.c
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@@ -7564,6 +7564,20 @@ uint64_t x86_cpu_get_supported_feature_word(X86CPU *cpu, FeatureWord w)
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#endif
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break;
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+ case FEAT_7_0_EDX:
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+ /*
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+ * Windows does not like ARCH_CAPABILITIES on AMD machines at all.
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+ * Do not show the fake ARCH_CAPABILITIES MSR that KVM sets up,
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+ * except if needed for migration.
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+ *
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+ * When arch_cap_always_on is removed, this tweak can move to
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+ * kvm_arch_get_supported_cpuid.
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+ */
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+ if (cpu && IS_AMD_CPU(&cpu->env) && !cpu->arch_cap_always_on) {
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+ unavail = CPUID_7_0_EDX_ARCH_CAPABILITIES;
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+ }
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+ break;
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+
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default:
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break;
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}
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@@ -10029,6 +10043,9 @@ static const Property x86_cpu_properties[] = {
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true),
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DEFINE_PROP_BOOL("x-l1-cache-per-thread", X86CPU, l1_cache_per_core, true),
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DEFINE_PROP_BOOL("x-force-cpuid-0x1f", X86CPU, force_cpuid_0x1f, false),
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+
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+ DEFINE_PROP_BOOL("x-arch-cap-always-on", X86CPU,
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+ arch_cap_always_on, false),
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};
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#ifndef CONFIG_USER_ONLY
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diff --git a/target/i386/cpu.h b/target/i386/cpu.h
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index f977fc49a7..b966bc997c 100644
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--- a/target/i386/cpu.h
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+++ b/target/i386/cpu.h
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@@ -2314,6 +2314,12 @@ struct ArchCPU {
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/* Forcefully disable KVM PV features not exposed in guest CPUIDs */
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bool kvm_pv_enforce_cpuid;
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+ /*
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+ * Expose arch-capabilities unconditionally even on AMD models, for backwards
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+ * compatibility with QEMU <10.1.
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+ */
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+ bool arch_cap_always_on;
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+
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/* Number of physical address bits supported */
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uint32_t phys_bits;
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diff --git a/target/i386/kvm/kvm.c b/target/i386/kvm/kvm.c
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index 0eb39d22d6..baa2f80beb 100644
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--- a/target/i386/kvm/kvm.c
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+++ b/target/i386/kvm/kvm.c
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@@ -503,12 +503,8 @@ uint32_t kvm_arch_get_supported_cpuid(KVMState *s, uint32_t function,
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* Linux v4.17-v4.20 incorrectly return ARCH_CAPABILITIES on SVM hosts.
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* We can detect the bug by checking if MSR_IA32_ARCH_CAPABILITIES is
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* returned by KVM_GET_MSR_INDEX_LIST.
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- *
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- * But also, because Windows does not like ARCH_CAPABILITIES on AMD
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- * mcahines at all, do not show the fake ARCH_CAPABILITIES MSR that
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- * KVM sets up.
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*/
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- if (!has_msr_arch_capabs || !(edx & CPUID_7_0_EDX_ARCH_CAPABILITIES)) {
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+ if (!has_msr_arch_capabs) {
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ret &= ~CPUID_7_0_EDX_ARCH_CAPABILITIES;
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}
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} else if (function == 7 && index == 1 && reg == R_EAX) {
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