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From: David Woodhouse <dwmw2@infradead.org>
To: Brian Gerst <brgerst@gmail.com>, Usama Arif <usama.arif@bytedance.com>
Cc: tglx@linutronix.de, kim.phillips@amd.com,
	piotrgorski@cachyos.org, oleksandr@natalenko.name,
	arjan@linux.intel.com, 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, gpiccoli@igalia.com
Subject: Re: [PATCH v15 09/12] x86/smpboot: Support parallel startup of secondary CPUs
Date: Tue, 21 Mar 2023 19:12:06 +0000	[thread overview]
Message-ID: <30efad7b8a5922cdaa48ab89a2dbaf425daf49a8.camel@infradead.org> (raw)
In-Reply-To: <CAMzpN2jMyLP9h5o_wwdThHipAns2_dx3Nf8JYhj5pEqaeWXqYg@mail.gmail.com>

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On Tue, 2023-03-21 at 14:28 -0400, Brian Gerst wrote:
> 
> > @@ -264,6 +318,14 @@ SYM_INNER_LABEL(secondary_startup_64_no_verify, SYM_L_GLOBAL)
> >          lgdt    (%rsp)
> >          addq    $16, %rsp
> > 
> > +       /* Drop the realmode protection. For the boot CPU the pointer is NULL! */
> > +       movq    trampoline_lock(%rip), %rax
> > +       testq   %rax, %rax
> > +       jz      .Lsetup_data_segments
> > +       lock
> > +       btrl    $0, (%rax)
> > +
> > +.Lsetup_data_segments:
> >          /* set up data segments */
> >          xorl %eax,%eax
> >          movl %eax,%ds
> 
> This can still go earlier, right after "movq TASK_threadsp(%rax),
> %rsp".  The GDT descriptor is placed on the idle thread stack, so it's
> safe to drop the lock before it.


--- a/arch/x86/kernel/head_64.S
+++ b/arch/x86/kernel/head_64.S
@@ -335,6 +335,17 @@ SYM_INNER_LABEL(secondary_startup_64_no_verify, SYM_L_GLOBAL)
        movq    pcpu_hot + X86_current_task(%rdx), %rax
        movq    TASK_threadsp(%rax), %rsp
 
+       /*
+        * Now that this CPU is running on its own stack, drop the realmode
+        * protection. For the boot CPU the pointer is NULL!
+        */
+       movq    trampoline_lock(%rip), %rax
+       testq   %rax, %rax
+       jz      .Lsetup_gdt
+       lock
+       btrl    $0, (%rax)
+
+.Lsetup_gdt:
        /*
         * We must switch to a new descriptor in kernel space for the GDT
         * because soon the kernel won't have access anymore to the userspace
@@ -377,14 +388,6 @@ SYM_INNER_LABEL(secondary_startup_64_no_verify, SYM_L_GLOBAL)
        shrq    $32, %rdx
        wrmsr
 
-       /* Drop the realmode protection. For the boot CPU the pointer is NULL! */
-       movq    trampoline_lock(%rip), %rax
-       testq   %rax, %rax
-       jz      .Lsetup_idt
-       lock
-       btrl    $0, (%rax)
-
-.Lsetup_idt:
        /* Setup and Load IDT */
        pushq   %rsi
        call    early_setup_idt


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  reply	other threads:[~2023-03-21 19:14 UTC|newest]

Thread overview: 29+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2023-03-16 22:20 [PATCH v15 00/12] Parallel CPU bringup for x86_64 Usama Arif
2023-03-16 22:20 ` [PATCH v15 01/12] x86/apic/x2apic: Allow CPU cluster_mask to be populated in parallel Usama Arif
2023-03-21 14:14   ` [tip: x86/apic] " tip-bot2 for David Woodhouse
2023-03-16 22:20 ` [PATCH v15 02/12] cpu/hotplug: Move idle_thread_get() to <linux/smpboot.h> Usama Arif
2023-03-19 16:34   ` Borislav Petkov
2023-03-20  8:17     ` David Woodhouse
2023-03-21 19:20       ` David Woodhouse
2023-03-16 22:21 ` [PATCH v15 03/12] cpu/hotplug: Add dynamic parallel bringup states before CPUHP_BRINGUP_CPU Usama Arif
2023-03-20 14:30   ` Thomas Gleixner
2023-03-21 19:14     ` David Woodhouse
2023-03-16 22:21 ` [PATCH v15 04/12] x86/smpboot: Reference count on smpboot_setup_warm_reset_vector() Usama Arif
2023-03-21 11:41   ` Borislav Petkov
2023-03-21 11:43     ` David Woodhouse
2023-03-21 14:14   ` [tip: x86/apic] " tip-bot2 for David Woodhouse
2023-03-16 22:21 ` [PATCH v15 05/12] x86/smpboot: Split up native_cpu_up into separate phases and document them Usama Arif
2023-03-16 22:21 ` [PATCH v15 06/12] x86/smpboot: Remove initial_stack on 64-bit Usama Arif
2023-03-21 14:14   ` [tip: x86/apic] " tip-bot2 for Brian Gerst
2023-03-16 22:21 ` [PATCH v15 07/12] x86/smpboot: Remove early_gdt_descr " Usama Arif
2023-03-21 14:14   ` [tip: x86/apic] " tip-bot2 for Brian Gerst
2023-03-16 22:21 ` [PATCH v15 08/12] x86/smpboot: Remove initial_gs Usama Arif
2023-03-21 14:14   ` [tip: x86/apic] " tip-bot2 for Brian Gerst
2023-03-16 22:21 ` [PATCH v15 09/12] x86/smpboot: Support parallel startup of secondary CPUs Usama Arif
2023-03-21 18:28   ` Brian Gerst
2023-03-21 19:12     ` David Woodhouse [this message]
2023-03-21 21:02       ` Brian Gerst
2023-03-16 22:21 ` [PATCH v15 10/12] x86/smpboot: Send INIT/SIPI/SIPI to secondary CPUs in parallel Usama Arif
2023-03-16 22:21 ` [PATCH v15 11/12] x86/smpboot: Serialize topology updates for secondary bringup Usama Arif
2023-03-16 22:21 ` [PATCH v15 12/12] x86/smpboot: Allow parallel bringup for SEV-ES Usama Arif
2023-03-17 16:04   ` Tom Lendacky

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