linux-kernel - Re: [PATCHv6 15/30] x86/boot: Port I/O: allow to hook up alternative helpers

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Date:   Thu, 17 Mar 2022 23:10:54 +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,
        thomas.lendacky@....com, brijesh.singh@....com, x86@...nel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCHv6 15/30] x86/boot: Port I/O: allow to hook up alternative
 helpers

On Thu, Mar 17, 2022 at 01:12:59PM +0100, Thomas Gleixner wrote:
> On Wed, Mar 16 2022 at 05:08, Kirill A. Shutemov wrote:
> > +#undef inb
> > +#undef inw
> > +#undef inl
> > +#undef outb
> > +#undef outw
> > +#undef outl
> > +
> > +struct port_io_ops {
> > +	u8 (*inb)(u16 port);
> > +	u16 (*inw)(u16 port);
> > +	u32 (*inl)(u16 port);
> > +	void (*outb)(u8 v, u16 port);
> > +	void (*outw)(u16 v, u16 port);
> > +	void (*outl)(u32 v, u16 port);
> 
> 	u8	(*inb)(u16 port);
> 	void	(*outb)(u8 v, u16 port);
> 	void	(*outw)(u16 v, u16 port);
> 
> is all what's used AFAICT.

Hm. Okay. I will drop the rest.

> > +};
> > +
> > +extern struct port_io_ops pio_ops;
> > +
> > +/*
> > + * Use the normal I/O instructions by default.
> > + * TDX guests override these to use hypercalls.
> > + */
> > +static inline void init_default_io_ops(void)
> > +{
> > +	pio_ops.inb = __inb;
> > +	pio_ops.inw = __inw;
> > +	pio_ops.inl = __inl;
> > +	pio_ops.outb = __outb;
> > +	pio_ops.outw = __outw;
> > +	pio_ops.outl = __outl;
> > +}
> 
> #define DEFINE_PORT_IO_OPS()		\
> 	struct port_io_ops pio_ops = {	\
>         	.inb	= __inb,	\
>         	.outb	= __outb,	\
>         	.outw	= __outw, }
> 
> Hmm?

This kind of initializations are problematic. They generate run-time
relacations that kernel cannot handle in the boot stub. Linker complains
about this:

	ld.lld: error: Unexpected run-time relocations (.rela) detected!

I will leave it as is, unless you have better ideas.

-- 
 Kirill A. Shutemov