Re: [tip:x86/setup] x86, setup: "glove box" BIOS calls --infrastructure

[Pavel Machek]

Hi!

> x86, setup: "glove box" BIOS calls -- infrastructure
> 
> Impact: new interfaces (not yet used)
> 
> For all the platforms out there, there is an infinite number of buggy
> BIOSes.  This adds infrastructure to treat BIOS interrupts more like
> toxic waste and "glove box" them -- we switch out the register set,
> perform the BIOS interrupt, and then restore the previous state.
> 
> LKML-Reference: <49DE7F79.4030106@xxxxxxxxx>
> Signed-off-by: H. Peter Anvin <hpa@xxxxxxxxxxxxxxx>
> Cc: Pavel Machek <pavel@xxxxxx>

Sounds quite sane. Disadvantage is that we will no longer detect those
buggy BIOSen.

> +/*
> + * "Glove box" for BIOS calls.  Avoids the constant problems with BIOSes
> + * touching memory they shouldn't be.
> + */

Touching memory? AFAICT it only prevents touching registers.

> +	.code16
> +	.text
> +	.globl	intcall
> +	.type	intcall, @function
> +intcall:
> +	/* Self-modify the INT instruction.  Ugly, but works. */
> +	cmpb	%al, 3f
> +	je	1f
> +	movb	%al, 3f
> +	jmp	1f		/* Synchronize pipeline */
> +1:

There are various CPU bugs with self-modifying code, but I guess we
are not using it heavily enough. Also we are single-threaded so that
should be ok.
								Pavel

-- 
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