Message-ID: <675d56c5e9dbbe32a0142a3a5290b0c35c52c568.camel@infradead.org>
Subject: Re: [PATCH v6 07/11] x86/smpboot: Disable parallel boot for AMD CPUs
From:   David Woodhouse <dwmw2@infradead.org>
To:     Kim Phillips <kim.phillips@amd.com>,
        Usama Arif <usama.arif@bytedance.com>, tglx@linutronix.de,
        arjan@linux.intel.com
Cc:     mingo@redhat.com, bp@alien8.de, dave.hansen@linux.intel.com,
        hpa@zytor.com, x86@kernel.org, pbonzini@redhat.com,
        paulmck@kernel.org, linux-kernel@vger.kernel.org,
        kvm@vger.kernel.org, rcu@vger.kernel.org, mimoja@mimoja.de,
        hewenliang4@huawei.com, thomas.lendacky@amd.com, seanjc@google.com,
        pmenzel@molgen.mpg.de, fam.zheng@bytedance.com,
        punit.agrawal@bytedance.com, simon.evans@bytedance.com,
        liangma@liangbit.com, Mario Limonciello <Mario.Limonciello@amd.com>
Date:   Sat, 04 Feb 2023 10:09:00 +0000
In-Reply-To: <b3d9fbbf-e760-5d1d-9182-44c144abd1bf@amd.com>
References: <20230202215625.3248306-1-usama.arif@bytedance.com>
         <20230202215625.3248306-8-usama.arif@bytedance.com>
         <b3d9fbbf-e760-5d1d-9182-44c144abd1bf@amd.com>
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On Fri, 2023-02-03 at 13:48 -0600, Kim Phillips wrote:
> [=C2=A0=C2=A0=C2=A0 3.204580] [Firmware Bug]: CPU0: APIC id mismatch. Fir=
mware: 0
> APIC: 2


Could it just be that some processors have CPUID leaves above 0xb but
don't actually support 0xb?

What does this do?

--- a/arch/x86/kernel/smpboot.c
+++ b/arch/x86/kernel/smpboot.c
@@ -1578,6 +1578,18 @@ void __init native_smp_prepare_cpus(unsigned int max=
_cpus)
 	    cc_platform_has(CC_ATTR_GUEST_STATE_ENCRYPT))
 		do_parallel_bringup =3D false;
=20
+	if (do_parallel_bringup) {
+		/* Check that CPUID 0x0B really does look sane. */
+		unsigned int eax, ebx, ecx, edx;
+
+		cpuid_count(0xb, 0, &eax, &ebx, &ecx, &edx);
+		printk("CPUID 0xB level 0: %x %x %x %x\n", eax, ebx, ecx, edx);
+		if (!eax && !ebx) {
+			pr_info("Disabling parallel bringup because CPUID 0xb looks untrustwort=
hy\n");
+			do_parallel_bringup =3D false;
+		}
+	}
+
 	if (do_parallel_bringup &&
 	    boot_cpu_has_bug(X86_BUG_NO_PARALLEL_BRINGUP)) {
 		pr_info("Disabling parallel bringup due to CPU bugs\n");


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