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Tue, 23 Sep 2025 03:41:43 -0700 (PDT) X-Google-Smtp-Source: AGHT+IEaRQct4v6u6fwKFvJ5qxUMkG5X5B2BjOJRWuJk4kwB2ravZy8/qumoVfFXg4yw/aekmyIc+g== X-Received: by 2002:a17:907:7f13:b0:b07:88aa:255b with SMTP id a640c23a62f3a-b302689510bmr198563366b.11.1758624103507; Tue, 23 Sep 2025 03:41:43 -0700 (PDT) From: Paolo Bonzini To: qemu-devel@nongnu.org Cc: hector.cao@canonical.com, lk@c--e.de, berrange@redhat.com Subject: [RFT PATCH v2 2/2] target/i386: add compatibility property for pdcm feature Date: Tue, 23 Sep 2025 12:41:36 +0200 Message-ID: <20250923104136.133875-3-pbonzini@redhat.com> X-Mailer: git-send-email 2.51.0 In-Reply-To: <20250923104136.133875-1-pbonzini@redhat.com> References: <20250923104136.133875-1-pbonzini@redhat.com> MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Received-SPF: pass (zohomail.com: domain of gnu.org designates 209.51.188.17 as permitted sender) client-ip=209.51.188.17; envelope-from=qemu-devel-bounces+importer=patchew.org@nongnu.org; helo=lists.gnu.org; Received-SPF: pass client-ip=170.10.129.124; envelope-from=pbonzini@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -24 X-Spam_score: -2.5 X-Spam_bar: -- X-Spam_report: (-2.5 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.442, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H4=0.001, RCVD_IN_MSPIKE_WL=0.001, RCVD_IN_VALIDITY_CERTIFIED_BLOCKED=0.001, SPF_HELO_PASS=-0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+importer=patchew.org@nongnu.org Sender: qemu-devel-bounces+importer=patchew.org@nongnu.org X-ZohoMail-DKIM: pass (identity @redhat.com) X-ZM-MESSAGEID: 1758624154073116600 Content-Type: text/plain; charset="utf-8" From: Hector Cao 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 fea= ture_dependencies[] check", 2025-06-20) [Move property from migration object to CPU. - Paolo] Signed-off-by: Paolo Bonzini Reviewed-by: Zhao Liu --- target/i386/cpu.h | 6 ++++++ hw/i386/pc.c | 1 + target/i386/cpu.c | 15 ++++++++++++--- 3 files changed, 19 insertions(+), 3 deletions(-) diff --git a/target/i386/cpu.h b/target/i386/cpu.h index 414ca968e84..42168f1d6d8 100644 --- a/target/i386/cpu.h +++ b/target/i386/cpu.h @@ -2320,6 +2320,12 @@ struct ArchCPU { */ bool arch_cap_always_on; =20 + /* + * Backwards compatibility with QEMU <10.1. The PDCM feature is now di= sabled 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; =20 diff --git a/hw/i386/pc.c b/hw/i386/pc.c index d7f48150fdd..4668918746e 100644 --- a/hw/i386/pc.c +++ b/hw/i386/pc.c @@ -88,6 +88,7 @@ GlobalProperty pc_compat_10_0[] =3D { { 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 =3D G_N_ELEMENTS(pc_compat_10_0); =20 diff --git a/target/i386/cpu.c b/target/i386/cpu.c index fe369bb1284..ab18de894e4 100644 --- a/target/i386/cpu.c +++ b/target/i386/cpu.c @@ -7908,6 +7908,11 @@ void cpu_x86_cpuid(CPUX86State *env, uint32_t index,= uint32_t count, /* Fixup overflow: max value for bits 23-16 is 255. */ *ebx |=3D MIN(num, 255) << 16; } + if (cpu->pdcm_on_even_without_pmu) { + if (!cpu->enable_pmu) { + *ecx &=3D ~CPUID_EXT_PDCM; + } + } break; case 2: { /* cache info: needed for Pentium Pro compatibility */ const CPUCaches *caches; @@ -8958,9 +8963,11 @@ void x86_cpu_expand_features(X86CPU *cpu, Error **er= rp) } } =20 - /* PDCM is fixed1 bit for TDX */ - if (!cpu->enable_pmu && !is_tdx_vm()) { - env->features[FEAT_1_ECX] &=3D ~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] &=3D ~CPUID_EXT_PDCM; + } } =20 for (i =3D 0; i < ARRAY_SIZE(feature_dependencies); i++) { @@ -10021,6 +10028,8 @@ static const Property x86_cpu_properties[] =3D { =20 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), }; =20 #ifndef CONFIG_USER_ONLY --=20 2.51.0