linux-kernel - Re: [PATCHv7 21/30] x86/acpi, x86/boot: Add multiprocessor wake-up support

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Date:   Fri, 1 Apr 2022 10:33:39 -0700
From:   Dave Hansen <dave.hansen@...el.com>
To:     "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
Cc:     tglx@...utronix.de, mingo@...hat.com, bp@...en8.de,
        luto@...nel.org, peterz@...radead.org,
        sathyanarayanan.kuppuswamy@...ux.intel.com, aarcange@...hat.com,
        ak@...ux.intel.com, dan.j.williams@...el.com, david@...hat.com,
        hpa@...or.com, jgross@...e.com, jmattson@...gle.com,
        joro@...tes.org, jpoimboe@...hat.com, knsathya@...nel.org,
        pbonzini@...hat.com, sdeep@...are.com, seanjc@...gle.com,
        tony.luck@...el.com, vkuznets@...hat.com, wanpengli@...cent.com,
        thomas.lendacky@....com, brijesh.singh@....com, x86@...nel.org,
        linux-kernel@...r.kernel.org,
        Sean Christopherson <sean.j.christopherson@...el.com>,
        "Rafael J . Wysocki" <rafael.j.wysocki@...el.com>
Subject: Re: [PATCHv7 21/30] x86/acpi, x86/boot: Add multiprocessor wake-up
 support

On 3/30/22 18:52, Kirill A. Shutemov wrote:
> 
>>>From ab320371f9ef8d24722394ec2505089e68737527 Mon Sep 17 00:00:00 2001
> From: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@...ux.intel.com>
> Date: Thu, 15 Apr 2021 10:31:38 -0700
> Subject: [PATCH] x86/acpi, x86/boot: Add multiprocessor wake-up support
> 
> Secondary CPU startup is currently performed with something called
> the "INIT/SIPI protocol".  This protocol requires assistance from
> VMMs to boot guests.  As should be a familiar story by now, that
> support can not be provded to TDX guests because TDX VMMs are
> not trusted by guests.
> 
> To remedy this situation a new[1] "Multiprocessor Wakeup Structure"
> has been added to to an existing ACPI table (MADT).  This structure
> provides the physical address of a "mailbox".  A write to the mailbox
> then steers the secondary CPU to the boot code.
> 
> Add ACPI MADT wake structure parsing support and wake support.  Use
> this support to wake CPUs whenever it is present instead of INIT/SIPI.
> 
> While this structure can theoretically be used on 32-bit kernels,
> there are no 32-bit TDX guest kernels.  It has not been tested and
> can not practically *be* tested on 32-bit.  Make it 64-bit only.
> 
> 1. Details about the new structure can be found in ACPI v6.4, in the
>    "Multiprocessor Wakeup Structure" section.
> 
> Co-developed-by: Sean Christopherson <sean.j.christopherson@...el.com>
> Signed-off-by: Sean Christopherson <sean.j.christopherson@...el.com>
> Reviewed-by: Andi Kleen <ak@...ux.intel.com>
> Reviewed-by: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
> Signed-off-by: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@...ux.intel.com>
> Signed-off-by: Kirill A. Shutemov <kirill.shutemov@...ux.intel.com>

Looks good.  I'm glad you were able to get rid of the extra-wakeup
checks too.

Reviewed-by: Dave Hansen <dave.hansen@...ux.intel.com>