linux-kernel - Re: [BUG + PATCH/Bugfix] x86/lguest: fix pgdir pmd index calculation

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Date:	Tue, 4 Mar 2008 23:06:57 +1100
From:	Rusty Russell <rusty@...tcorp.com.au>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	"Ahmed S. Darwish" <darwish.07@...il.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	LKML <linux-kernel@...r.kernel.org>, lguest@...abs.org,
	akpm <akpm@...ux-foundation.org>,
	Jeremy Fitzhardinge <jeremy@...source.com>
Subject: Re: [BUG + PATCH/Bugfix] x86/lguest: fix pgdir pmd index calculation

On Saturday 01 March 2008 06:58:38 Ingo Molnar wrote:
> * Ahmed S. Darwish <darwish.07@...il.com> wrote:
> > On the lguest _guest_ side, 'cpu_has_tsc' is _always_ false (due to
> > lguest using his own clocksource ?), thus a guest with a pentium+ cpu
> > always panics with:
>
> does the "RDTSC" instruction work in an lguest guest? If not, then the
> lguest kernel is correct in not exposing it - and then the solution is
> to build a non-TSC guest kernel. Does the patch below help?
>
> but if the RDTSC instruction does work in an lguest guest, then the
> proper approach would be to expose it in the CPU features.

Yes, and after some investigation, I came up with two patches.  I'll queue 
both to you if that's ok, since they're dependent.

When lguest was being developed we didn't have a get_tsc_khz hook, so I had to 
kill the TSC cpuid bit.  Nowdays, the code can actually be much more natural: 
the Host tells us the cpu khz, and if it's zero, we fall back to the 
dumb "lguest" clock.

Thanks,
Rusty.
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