linux-kernel - Re: [PATCH 7 of 13] Make __FIXADDR_TOP variable to allow it to make space for a hypervisor

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Date:	Wed, 02 Aug 2006 17:20:05 +1000
From:	Rusty Russell <rusty@...tcorp.com.au>
To:	Chris Wright <chrisw@...s-sol.org>
Cc:	Andrew Morton <akpm@...l.org>, jeremy@...source.com,
	linux-kernel@...r.kernel.org, Christian.Limpach@...cam.ac.uk,
	clameter@....com, ebiederm@...ssion.com, kraxel@...e.de,
	hollisb@...ibm.com, ian.pratt@...source.com, zach@...are.com
Subject: Re: [PATCH 7 of 13] Make __FIXADDR_TOP variable to allow it to
	make space for a hypervisor

On Wed, 2006-08-02 at 00:01 -0700, Chris Wright wrote:
> Here's an updated patch.  Rather than use __FIXADDR_TOP to adjust for
> MAXMEM, directly update __VMALLOC_RESERVE which is used to reserve the
> space for vmalloc, iomap, and fixmap (as comments aptly point out).  I
> tested this with a bunch of configurations, and booted a XenoLinux
> kernel with this patch as well.

Just one minor point:

> +void set_fixaddr_top(unsigned long top)
> +{
> +	BUG_ON(fixmaps > 0);
> +#ifdef CONFIG_COMPAT_VDSO
> +	BUG_ON(top - PAGE_SIZE != __FIXADDR_TOP);
> +#else
> +	__FIXADDR_TOP = top - PAGE_SIZE;
> +	__VMALLOC_RESERVE -= top;
> +#endif
>  }

This no longer seems to be an appropriate name.  How about
set_address_top_reserve or something?

void set_address_top_reserve(unsigned long reserve)
{
	BUG_ON(fixmaps > 0);
#ifdef CONFIG_COMPAT_VDSO
	BUG_ON(reserve != 0);
#else
	__FIXADDR_TOP = -reserve - PAGE_SIZE;
	__VMALLOC_RESERVE += reserve;
#endif
}

(I *think* I got the logic here correct).

Rusty.
-- 
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