linux-kernel - Re: [PATCHv2 11/29] x86/boot: Allow to hook up alternative port I/O helpers

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Date:   Tue, 01 Feb 2022 23:39:09 +0100
From:   Thomas Gleixner <tglx@...utronix.de>
To:     "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        mingo@...hat.com, bp@...en8.de, dave.hansen@...el.com,
        luto@...nel.org, peterz@...radead.org
Cc:     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,
        x86@...nel.org, linux-kernel@...r.kernel.org,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
Subject: Re: [PATCHv2 11/29] x86/boot: Allow to hook up alternative port I/O
 helpers

On Mon, Jan 24 2022 at 18:01, Kirill A. Shutemov wrote:

> Port I/O instructions trigger #VE in the TDX environment. In response to
> the exception, kernel emulates these instructions using hypercalls.
>
> But during early boot, on the decompression stage, it is cumbersome to
> deal with #VE. It is cleaner to go to hypercalls directly, bypassing #VE
> handling.
>
> Add a way to hook up alternative port I/O helpers in the boot stub.
> All port I/O operations are routed via 'pio_ops'. By default 'pio_ops'
> initialized with native port I/O implementations.
>
> This is a preparation patch. The next patch will override 'pio_ops' if
> the kernel booted in the TDX environment.
>
> Signed-off-by: Kirill A. Shutemov <kirill.shutemov@...ux.intel.com>

Aside of Borislav's comments:

Reviewed-by: Thomas Gleixner <tglx@...utronix.de>