linux-kernel - Re: [PATCH v3 3/3] x86/acpi, x86/boot: Add multiprocessor wake-up support

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Message-ID: <20210510172237.GU4032392@tassilo.jf.intel.com>
Date:   Mon, 10 May 2021 10:22:37 -0700
From:   Andi Kleen <ak@...ux.intel.com>
To:     "Kuppuswamy, Sathyanarayanan" 
        <sathyanarayanan.kuppuswamy@...ux.intel.com>
Cc:     "Rafael J. Wysocki" <rafael@...nel.org>,
        Rafael J Wysocki <rjw@...ysocki.net>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        "H . Peter Anvin" <hpa@...or.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Len Brown <lenb@...nel.org>,
        Robert Moore <robert.moore@...el.com>,
        Erik Kaneda <erik.kaneda@...el.com>,
        ACPI Devel Maling List <linux-acpi@...r.kernel.org>,
        "open list:ACPI COMPONENT ARCHITECTURE (ACPICA)" <devel@...ica.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        the arch/x86 maintainers <x86@...nel.org>,
        Sean Christopherson <sean.j.christopherson@...el.com>
Subject: Re: [PATCH v3 3/3] x86/acpi, x86/boot: Add multiprocessor wake-up
 support

On Mon, May 10, 2021 at 10:10:24AM -0700, Kuppuswamy, Sathyanarayanan wrote:
> 
> 
> On 5/10/21 9:55 AM, Rafael J. Wysocki wrote:
> > I'm not sure how my comment regarding the fact that for a given CPU
> > this function is only usable once has been addressed.
> > 
> > While it may not be a practical concern in the use case that you are
> > after (TDX), this is a generic mechanism and it needs to cover other
> > possible usage scenarios.
> 
> For the same CPU, if we try to use mailbox again, firmware will not
> respond to it. So the command will timeout and return error.

Right because the firmware code doesn't run anymore.

The only possibility would be for Linux to put back some code that spins
and waits again, but that would be quite pointless and wasteful.

-Andi