linux-kernel - Re: [patch v3 33/36] x86/apic: Save the APIC virtual base address

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Message-ID: <a6f48a7b-484c-31af-f568-cb1de0d766d4@omp.ru>
Date:   Tue, 9 May 2023 12:20:06 +0300
From:   Sergey Shtylyov <s.shtylyov@....ru>
To:     Thomas Gleixner <tglx@...utronix.de>,
        LKML <linux-kernel@...r.kernel.org>
CC:     <x86@...nel.org>, David Woodhouse <dwmw2@...radead.org>,
        Andrew Cooper <andrew.cooper3@...rix.com>,
        Brian Gerst <brgerst@...il.com>,
        Arjan van de Veen <arjan@...ux.intel.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Paul McKenney <paulmck@...nel.org>,
        Tom Lendacky <thomas.lendacky@....com>,
        Sean Christopherson <seanjc@...gle.com>,
        Oleksandr Natalenko <oleksandr@...alenko.name>,
        Paul Menzel <pmenzel@...gen.mpg.de>,
        "Guilherme G. Piccoli" <gpiccoli@...lia.com>,
        Piotr Gorski <lucjan.lucjanov@...il.com>,
        Usama Arif <usama.arif@...edance.com>,
        Juergen Gross <jgross@...e.com>,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        <xen-devel@...ts.xenproject.org>,
        Russell King <linux@...linux.org.uk>,
        Arnd Bergmann <arnd@...db.de>,
        <linux-arm-kernel@...ts.infradead.org>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>, Guo Ren <guoren@...nel.org>,
        <linux-csky@...r.kernel.org>,
        Thomas Bogendoerfer <tsbogend@...ha.franken.de>,
        <linux-mips@...r.kernel.org>,
        "James E.J. Bottomley" <James.Bottomley@...senPartnership.com>,
        Helge Deller <deller@....de>, <linux-parisc@...r.kernel.org>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        Palmer Dabbelt <palmer@...belt.com>,
        <linux-riscv@...ts.infradead.org>,
        Mark Rutland <mark.rutland@....com>,
        Sabin Rapan <sabrapan@...zon.com>,
        "Michael Kelley (LINUX)" <mikelley@...rosoft.com>
Subject: Re: [patch v3 33/36] x86/apic: Save the APIC virtual base address

Hello!

On 5/8/23 10:44 PM, Thomas Gleixner wrote:

> From: Thomas Gleixner <tglx@...utronix.de>
> 
> For parallel CPU brinugp it's required to read the APIC ID in the low level
> startup code. The virtual APIC base address is a constant because its a
> fix-mapped address. Exposing that constant which is composed via macros to
> assembly code is non-trivial dues to header inclusion hell.

   s/dues/due/?

> Aside of that it's constant only because of the vsyscall ABI
> requirement. Once vsyscall is out of the picture the fixmap can be placed
> at runtime.
> 
> Avoid header hell, stay flexible and store the address in a variable which
> can be exposed to the low level startup code.
> 
> Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
> Tested-by: Michael Kelley <mikelley@...rosoft.com>

[...]

MBR, Sergey