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 23:53:28 +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 Tue, Feb 01 2022 at 23:39, Thomas Gleixner wrote:

> 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>

Second thoughts.

> +#include <asm/shared/io.h>
> +
> +struct port_io_ops {
> +	unsigned char (*inb)(int port);
> +	unsigned short (*inw)(int port);
> +	unsigned int (*inl)(int port);
> +	void (*outb)(unsigned char v, int port);
> +	void (*outw)(unsigned short v, int port);
> +	void (*outl)(unsigned int v, int port);
> +};

Can we please make that u8, u16, u32 instead of unsigned char,short,int?

That's the kernel convention for hardware related functions for many
years now.

Thanks,

        tglx