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

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Date:   Wed, 2 Feb 2022 20:20:26 +0300
From:   "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     mingo@...hat.com, bp@...en8.de, dave.hansen@...el.com,
        luto@...nel.org, peterz@...radead.org,
        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
Subject: Re: [PATCHv2 11/29] x86/boot: Allow to hook up alternative port I/O
 helpers

On Tue, Feb 01, 2022 at 11:53:28PM +0100, Thomas Gleixner wrote:
> 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.

I inherited these prototypes from the main kernel I/O helpers. See patch
10/29.

Do you want 10/29 to be changed to use u8/16/32?

Maybe a separate patch to convert main kernel to u8/16/32 before
consolidation with boot stub?

-- 
 Kirill A. Shutemov