linux-kernel - Re: [patch] paravirt: VDSO page is essential

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Date:	Tue,  6 Mar 2007 01:13:07 -0800 (PST)
From:	Roland McGrath <roland@...hat.com>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	Jeremy Fitzhardinge <jeremy@...p.org>, Andi Kleen <ak@...e.de>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org,
	Rusty Russell <rusty@...tcorp.com.au>,
	Jan Beulich <jbeulich@...ell.com>
Subject: Re: [patch] paravirt: VDSO page is essential

> -# define VDSO_PRELINK          VDSO_HIGH_BASE
> +# ifndef CONFIG_XEN
> +#  define VDSO_PRELINK         VDSO_HIGH_BASE
> +# else
> +#  define VDSO_PRELINK         (0UL - FIX_VDSO * PAGE_SIZE)
> +# endif
> 
> should be Kconfig driven, not #ifdef driven, due to cleanliness and also 
> because lguest wants to have the same thing. Plus:

In fact, with the relocate_vdso stuff it doesn't matter what VDSO_PRELINK
is at compile time.  It saves the small amount of startup cost if it
matches the runtime address, but that is probably not noticeable.

> furthermore, there should be a paravirt_ops method to chose the 
> relocation address, unless i'm missing something. On the native kernel 
> that address will default to 0xffffe000. (if CONFIG_COMPAT_VDSO is 
> selected)

For everything else to work, it needs to be set by changing __FIXADDR_TOP,
which seems to be done by calling reserve_top_address early enough.
It looks like that needs to be properly tied into paravirt_ops somehow.


Thanks,
Roland
-
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