From: "Ahmed S. Darwish" <darwish.07@gmail.com>
To: Rusty Russell <rusty@rustcorp.com.au>
Cc: Thomas Gleixner <tglx@linutronix.de>,
Ingo Molnar <mingo@redhat.com>, "H. Peter Anvin" <hpa@zytor.com>,
LKML <linux-kernel@vger.kernel.org>,
lguest@ozlabs.org, akpm <akpm@linux-foundation.org>
Subject: Re: [BUG + PATCH/Bugfix] x86/lguest: fix pgdir pmd index calculation
Date: Tue, 4 Mar 2008 17:11:39 +0200 [thread overview]
Message-ID: <20080304151139.GA29618@ubuntu> (raw)
In-Reply-To: <200803042355.10960.rusty@rustcorp.com.au>
On Tue, Mar 04, 2008 at 11:55:10PM +1100, Rusty Russell wrote:
> On Monday 25 February 2008 02:55:15 Ahmed S. Darwish wrote:
> > Hi all,
> >
> > Beginning from commits close to v2.6.25-rc2, running lguest always oopses
> > the host kernel. Oops is at [1].
>
> OK, whatever the guest does should not break the host. So your patch can't be
> the whole solution.
>
> > static void lguest_set_pmd(pmd_t *pmdp, pmd_t pmdval)
> > {
> > *pmdp = pmdval;
> > lazy_hcall(LHCALL_SET_PMD, __pa(pmdp)&PAGE_MASK,
> > (__pa(pmdp)&(PAGE_SIZE-1))/4, 0);
> > }
> >
> > The first hcall parameter is global pgdir which looks fine. The second
> > parameter is the pmd index in the pgdir which is suspectful.
> >
> > AFAIK, calculating the index of pmd does not need a divisoin over four.
> > Removing the division made lguest work fine again . Patch is at [2].
>
> Each pmd is 4 bytes long, so the divide by 4 gives the index into the (top
> level) page. ie. a number in the range 0 to 1023.
>
aha, now it's clear.
>
> Indeed, here's the correct fix. Does it work for you?
>
Yes it does (after removing the unrelated TSC-if-pentium+ checks).
Thank you
--
"Better to light a candle, than curse the darkness"
Ahmed S. Darwish
Homepage: http://darwish.07.googlepages.com
Blog: http://darwish-07.blogspot.com
prev parent reply other threads:[~2008-03-04 15:15 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2008-02-24 15:55 [BUG + PATCH/Bugfix] x86/lguest: fix pgdir pmd index calculation Ahmed S. Darwish
2008-02-24 16:18 ` Ingo Molnar
2008-02-24 16:26 ` Ahmed S. Darwish
2008-02-25 0:18 ` Ahmed S. Darwish
2008-02-29 0:32 ` Ahmed S. Darwish
2008-02-29 19:58 ` Ingo Molnar
2008-03-04 6:37 ` Rusty Russell
2008-03-04 12:06 ` Rusty Russell
2008-03-04 12:07 ` [PATCH 1/2] x86: If we cannot calibrate the TSC, we panic Rusty Russell
2008-03-04 12:11 ` [PATCH 2/2] lguest: sanitize the clock Rusty Russell
2008-03-04 12:55 ` [BUG + PATCH/Bugfix] x86/lguest: fix pgdir pmd index calculation Rusty Russell
2008-03-04 15:11 ` Ahmed S. Darwish [this message]
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