From: Tim Deegan <tim@xen.org>
To: Bob Jung <Bob.Jung@mandiant.com>
Cc: "xen-devel@lists.xensource.com" <xen-devel@lists.xensource.com>
Subject: Re: potential bug where mem_event_request_t gfn value == -1?
Date: Mon, 9 Jan 2012 10:02:29 +0000 [thread overview]
Message-ID: <20120109100229.GD26595@ocelot.phlegethon.org> (raw)
In-Reply-To: <CC85277B-4FC1-4296-867C-971234973298@mandiant.com>
At 20:49 +0000 on 06 Jan (1325882993), Bob Jung wrote:
>
> Hi there,
>
> I am running an adapted version of tools/tests/xen_access/xen_access.c to get and respond to memory events to do some analysis. Anyways, after registering for and receiving single stepping events in my ring buffer where the me_event_request_t's reason field == MEM_EVENT_REASON_SINGLESTEP, I sometimes see that the gfn in the request is -1.
>
> the guest is HVM windows 32 bit. For 99.99% of the single step traps the req.gfn value is the correct guest frame number value, but every now and again I get a -1
>
> Does anyone know why this could happen?
If could happen if the VA in %rip at the time isn't mapped to anything
in the guest's pagetables (for example, if the guest is demand-paging
the program that's running). You should be able to test this by looking
at the valie if %rip returned in the gla field. There's some
pagetable-walking code in tools/libxc/xc_pagetab.c
Cheers,
Tim.
prev parent reply other threads:[~2012-01-09 10:02 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-01-06 20:49 potential bug where mem_event_request_t gfn value == -1? Bob Jung
2012-01-09 10:02 ` Tim Deegan [this message]
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