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[213.175.37.10]) by smtp.gmail.com with ESMTPSA id bm24-20020a170906c05800b006d58518e55fsm612760ejb.46.2022.03.16.02.04.26 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 16 Mar 2022 02:04:27 -0700 (PDT) Date: Wed, 16 Mar 2022 10:04:25 +0100 From: Igor Mammedov To: David Woodhouse Cc: qemu-devel@nongnu.org, "Michael S. Tsirkin" , Peter Xu , Jason Wang , Marcel Apfelbaum , Paolo Bonzini , Richard Henderson , Eduardo Habkost , Marcelo Tosatti , kvm@vger.kernel.org, Claudio Fontana , "Daniel P . =?UTF-8?B?QmVycmFuZ8Op?=" Subject: Re: [PATCH 1/4] target/i386: Fix sanity check on max APIC ID / X2APIC enablement Message-ID: <20220316100425.2758afc3@redhat.com> In-Reply-To: <20220314142544.150555-1-dwmw2@infradead.org> References: <20220314142544.150555-1-dwmw2@infradead.org> X-Mailer: Claws Mail 4.0.0 (GTK+ 3.24.31; x86_64-redhat-linux-gnu) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org On Mon, 14 Mar 2022 14:25:41 +0000 David Woodhouse wrote: > The check on x86ms->apic_id_limit in pc_machine_done() had two problems. > > Firstly, we need KVM to support the X2APIC API in order to allow IRQ > delivery to APICs >= 255. So we need to call/check kvm_enable_x2apic(), > which was done elsewhere in *some* cases but not all. > > Secondly, microvm needs the same check. So move it from pc_machine_done() > to x86_cpus_init() where it will work for both. > > The check in kvm_cpu_instance_init() is now redundant and can be dropped. Well, I retested with the latest upstream kernel (both guest and host), and adding kvm_enable_x2apic() is not sufficient as guest according to your patches in kernel caps max APICID at 255 unless kvm-msi-ext-dest-id is enabled. And attempt in enabling kvm-msi-ext-dest-id with kernel-irqchip fails. So number of usable CPUs in guest stays at legacy level, leaving the rest of CPUs in limbo. > Signed-off-by: David Woodhouse > Acked-by: Claudio Fontana > --- > hw/i386/pc.c | 8 -------- > hw/i386/x86.c | 16 ++++++++++++++++ > target/i386/kvm/kvm-cpu.c | 2 +- > 3 files changed, 17 insertions(+), 9 deletions(-) > > diff --git a/hw/i386/pc.c b/hw/i386/pc.c > index fd55fc725c..d3ab28fec5 100644 > --- a/hw/i386/pc.c > +++ b/hw/i386/pc.c > @@ -740,14 +740,6 @@ void pc_machine_done(Notifier *notifier, void *data) > /* update FW_CFG_NB_CPUS to account for -device added CPUs */ > fw_cfg_modify_i16(x86ms->fw_cfg, FW_CFG_NB_CPUS, x86ms->boot_cpus); > } > - > - > - if (x86ms->apic_id_limit > 255 && !xen_enabled() && > - !kvm_irqchip_in_kernel()) { > - error_report("current -smp configuration requires kernel " > - "irqchip support."); > - exit(EXIT_FAILURE); > - } > } > > void pc_guest_info_init(PCMachineState *pcms) > diff --git a/hw/i386/x86.c b/hw/i386/x86.c > index 4cf107baea..8da55d58ea 100644 > --- a/hw/i386/x86.c > +++ b/hw/i386/x86.c > @@ -39,6 +39,7 @@ > #include "sysemu/replay.h" > #include "sysemu/sysemu.h" > #include "sysemu/cpu-timers.h" > +#include "sysemu/xen.h" > #include "trace.h" > > #include "hw/i386/x86.h" > @@ -123,6 +124,21 @@ void x86_cpus_init(X86MachineState *x86ms, int default_cpu_version) > */ > x86ms->apic_id_limit = x86_cpu_apic_id_from_index(x86ms, > ms->smp.max_cpus - 1) + 1; > + > + /* > + * Can we support APIC ID 255 or higher? > + * > + * Under Xen: yes. > + * With userspace emulated lapic: no > + * With KVM's in-kernel lapic: only if X2APIC API is enabled. > + */ > + if (x86ms->apic_id_limit > 255 && !xen_enabled() && > + (!kvm_irqchip_in_kernel() || !kvm_enable_x2apic())) { > + error_report("current -smp configuration requires kernel " > + "irqchip and X2APIC API support."); > + exit(EXIT_FAILURE); > + } > + > possible_cpus = mc->possible_cpu_arch_ids(ms); > for (i = 0; i < ms->smp.cpus; i++) { > x86_cpu_new(x86ms, possible_cpus->cpus[i].arch_id, &error_fatal); > diff --git a/target/i386/kvm/kvm-cpu.c b/target/i386/kvm/kvm-cpu.c > index d95028018e..c60cb2dafb 100644 > --- a/target/i386/kvm/kvm-cpu.c > +++ b/target/i386/kvm/kvm-cpu.c > @@ -165,7 +165,7 @@ static void kvm_cpu_instance_init(CPUState *cs) > /* only applies to builtin_x86_defs cpus */ > if (!kvm_irqchip_in_kernel()) { > x86_cpu_change_kvm_default("x2apic", "off"); > - } else if (kvm_irqchip_is_split() && kvm_enable_x2apic()) { > + } else if (kvm_irqchip_is_split()) { > x86_cpu_change_kvm_default("kvm-msi-ext-dest-id", "on"); > } >