linux-kernel - Re: [PATCHv4 15/30] x86/boot: Allow to hook up alternative port I/O helpers

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Date:   Thu, 24 Feb 2022 14:14:02 -0800
From:   Dave Hansen <dave.hansen@...el.com>
To:     "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        tglx@...utronix.de, mingo@...hat.com, bp@...en8.de,
        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,
        thomas.lendacky@....com, brijesh.singh@....com, x86@...nel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCHv4 15/30] x86/boot: Allow to hook up alternative port I/O
 helpers

On 2/24/22 07:56, 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.

I'd add one more sentence to that:

... with a new pio_ops structure.  For now, set the ops structure to
just call the normal I/O operation functions.

But, either way:

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