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

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Date:	Mon, 05 Mar 2007 12:42:25 -0800
From:	Zachary Amsden <zach@...are.com>
To:	Ingo Molnar <mingo@...e.hu>
CC:	Andi Kleen <ak@...e.de>, Rusty Russell <rusty@...tcorp.com.au>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, Roland McGrath <roland@...hat.com>,
	virtualization <virtualization@...ts.osdl.org>
Subject: Re: [patch] paravirt: VDSO page is essential

Ingo Molnar wrote:
> there's no need to disable the VDSO for old userspace ...
>   

Well, apart from the obvious question to which nobody actually knows the 
answer, (how many people run old user space that required 
CONFIG_COMPAT_VDSO), what do you think of reversing the boot option?

vdso=enabled (default - turn on VDSO on normal boots)
vdso=disabled (turn off VDSO unconditionally)
[vdso=compat] (default for COMPAT_VDSO - keep VDSO only when mapped at 
compat location.  Note the option is not required to be implemented 
because it is logically implied from vdso=enabled && COMPAT_VDSO and the 
default boot behavior)
vdso=force (keep VDSO even when moved to a new location and COMPAT_VDSO 
is enabled).

In our case, installing VMware tools in the guest would then detect if 
userspace supports VDSO or if it requires COMPAT_VDSO and would then set 
boot parameters for the kernel appropriately.  And the native boot and 
kvm paravirt-ops boot are completely unaffected.

Zach
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