Re: unable to capture an expected page fault

[Study Xen <studyxen@gmail.com>]

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Hello Tim,

Thanks for your reply. I am actually learning (and the same time trying to
port) the code written by a former student. That is why it is currently
hard for me to clearly explain what have been modified in the code.

The former member's intention was to make use of Xen's ability of modifying
pagetables underneath the guest kernel to achieve data protection of user
applications from a compromised kernel. So his modification scattered into
several places, mainly in Xen's memory management code and interrupt
handling code. Unfortunately I have not been able to pinpoint which code
caused the current bug I mentioned in the previous mail.

X


On Tue, Jan 17, 2012 at 6:12 AM, Tim Deegan <tim@xen.org> wrote:

> Hi,
>
> At 03:08 -0500 on 17 Jan (1326769684), Study Xen wrote:
> > I was trying to modify part of Xen and faced a page fault missing issue.
> >
> > I am testing a PV Linux 64-bit guest (kernel 3.1.1, as dom0, the only
> > domain in my setting) atop Xen 4.1.2. In an unmodified Xen, the Linux
> > kernel's "native_set_pte" in "arch/x86/include/asm/pgtable_64.h" traps
> into
> > Xen due to Xen's write-protection of the pagetable page. But in our
> > modified version, this expected page fault seems missing.
>
> Well, I suppose it must be something you changed. :)  But since you don't
> say what you changed I'm not sure how much we can help you.  If the
> pagetables are indeed correct then maybe you're missing a TLB flush
> somewhere?
>
> Tim.
>

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