From 0d2ec98960c89003d3040818b5c5493cd636b98d Mon Sep 17 00:00:00 2001 From: Hector Cao Date: Tue, 23 Sep 2025 12:16:41 +0200 Subject: [PATCH 4/4] target/i386: add compatibility property for pdcm feature 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: [2/2] 9d76b45215d7ae2bc5ea2e61fe01780059d6d44c (bonzini/qemu-kvm-centos) JIRA: https://issues.redhat.com/browse/RHEL-120253 The pdcm feature is supposed to be disabled when PMU is not available. Up until v10.1, pdcm feature is enabled even when PMU is off. This behavior has been fixed but this change breaks the migration of VMs that are run with QEMU < 10.0 and expect the pdcm feature to be enabled on the destination host. This commit restores the legacy behavior for machines with version prior to 10.1 to allow the migration from older QEMU to QEMU 10.1. Signed-off-by: Hector Cao Link: https://lore.kernel.org/r/20250910115733.21149-3-hector.cao@canonical.com Fixes: e68ec298090 ("i386/cpu: Move adjustment of CPUID_EXT_PDCM before feature_dependencies[] check", 2025-06-20) [Move property from migration object to CPU. - Paolo] Signed-off-by: Paolo Bonzini (cherry picked from commit 6529f31e0dccadb532c80b36e3efe7aef83f9cad) Signed-off-by: Paolo Bonzini --- hw/i386/pc.c | 2 ++ target/i386/cpu.c | 15 ++++++++++++--- target/i386/cpu.h | 6 ++++++ 3 files changed, 20 insertions(+), 3 deletions(-) diff --git a/hw/i386/pc.c b/hw/i386/pc.c index 625a89d097..446d4a7c93 100644 --- a/hw/i386/pc.c +++ b/hw/i386/pc.c @@ -85,6 +85,7 @@ 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" }, + { TYPE_X86_CPU, "x-pdcm-on-even-without-pmu", "true" }, }; const size_t pc_compat_10_0_len = G_N_ELEMENTS(pc_compat_10_0); @@ -301,6 +302,7 @@ GlobalProperty pc_rhel_10_2_compat[] = { { 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" }, + { TYPE_X86_CPU, "x-pdcm-on-even-without-pmu", "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 de288dc5ac..dfcdfd3da6 100644 --- a/target/i386/cpu.c +++ b/target/i386/cpu.c @@ -7928,6 +7928,11 @@ void cpu_x86_cpuid(CPUX86State *env, uint32_t index, uint32_t count, /* Fixup overflow: max value for bits 23-16 is 255. */ *ebx |= MIN(num, 255) << 16; } + if (cpu->pdcm_on_even_without_pmu) { + if (!cpu->enable_pmu) { + *ecx &= ~CPUID_EXT_PDCM; + } + } break; case 2: { /* cache info: needed for Pentium Pro compatibility */ const CPUCaches *caches; @@ -8978,9 +8983,11 @@ void x86_cpu_expand_features(X86CPU *cpu, Error **errp) } } - /* PDCM is fixed1 bit for TDX */ - if (!cpu->enable_pmu && !is_tdx_vm()) { - env->features[FEAT_1_ECX] &= ~CPUID_EXT_PDCM; + if (!cpu->pdcm_on_even_without_pmu) { + /* PDCM is fixed1 bit for TDX */ + if (!cpu->enable_pmu && !is_tdx_vm()) { + env->features[FEAT_1_ECX] &= ~CPUID_EXT_PDCM; + } } for (i = 0; i < ARRAY_SIZE(feature_dependencies); i++) { @@ -10041,6 +10048,8 @@ static const Property x86_cpu_properties[] = { DEFINE_PROP_BOOL("x-arch-cap-always-on", X86CPU, arch_cap_always_on, false), + DEFINE_PROP_BOOL("x-pdcm-on-even-without-pmu", X86CPU, + pdcm_on_even_without_pmu, false), }; #ifndef CONFIG_USER_ONLY diff --git a/target/i386/cpu.h b/target/i386/cpu.h index b966bc997c..2187e61654 100644 --- a/target/i386/cpu.h +++ b/target/i386/cpu.h @@ -2320,6 +2320,12 @@ struct ArchCPU { */ bool arch_cap_always_on; + /* + * Backwards compatibility with QEMU <10.1. The PDCM feature is now disabled when + * PMU is not available, but prior to 10.1 it was enabled even if PMU is off. + */ + bool pdcm_on_even_without_pmu; + /* Number of physical address bits supported */ uint32_t phys_bits; -- 2.47.3