From mboxrd@z Thu Jan  1 00:00:00 1970
From: jeet <jeet_sat12@yahoo.co.in>
Subject: Re: page fault handling in Xen
Date: Mon, 5 Mar 2007 18:39:03 +0530 (IST)
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To: Keir Fraser <Keir.Fraser@cl.cam.ac.uk>, Tim Deegan <Tim.Deegan@xensource.com>
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Hi Keir =0A=0Athanks for your reply.I have some more queries=0A=0AIn HVM wh=
en guest is executing then processor looks into shadow page table for addre=
ss translation.=0Aas shadow PT contains the guest pt page readonly mapping =
of guest level 1 page table, on which guest OS is trying to write a address=
 of new page.    1=0Athis would cause second VMEXit in Xen. =0A=0Aso would =
faulting address be virtual address of that Guest PT page or of the shadow =
PT page which guest is trying to write?=0A=0Ajeet=0A=0A> Above code will ex=
ecute and in inner unlikely condition will be true as PT=0A> table is read =
only and  error is write_access=0A> and control will go to not_a_shadow_fau=
lt?=0A> =0A> so when the emulation code would be executed for the write tha=
t has been=0A> performed on read only guest PT for adding entry in=0A> gues=
t page table by guest?=0A> =0A> Have I missed some thing here in understand=
ing=0A=0AYes: guest PTs are mapped with write permissions in the guest PTs.=
 It's only=0Ain the shadow PTs that the guest PTs are mapped read-only. The=
 test on=0Aaccumulated_gflags is looking at the access permissions in the g=
uest PTs.=0A=0A -- Keir=0A=0A=0A=0A________________________________________=
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ists.xensource.com/xen-devel=0A=0A=0A=0A=0A=0A=09=09=0A____________________=
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