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Re: [Xen-devel] HYBRID: PV in HVM container

To: Mukesh Rathor <mukesh.rathor@xxxxxxxxxx>
Subject: Re: [Xen-devel] HYBRID: PV in HVM container
From: Keir Fraser <keir.xen@xxxxxxxxx>
Date: Sat, 09 Jul 2011 08:35:18 +0100
Cc: "Xen-devel@xxxxxxxxxxxxxxxxxxx" <Xen-devel@xxxxxxxxxxxxxxxxxxx>, Campbell <Ian.Campbell@xxxxxxxxxx>
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Thread-topic: [Xen-devel] HYBRID: PV in HVM container
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On 09/07/2011 02:53, "Mukesh Rathor" <mukesh.rathor@xxxxxxxxxx> wrote:

> where the only difference between N4 and N5 is that in N5 I've enabled
> vmexits only for page faults on write protection, ie, err code 0x3.
> I'm trying to figure out how vtlb implemention relates to SDM 28.3.5.
> It seems in xen, vtlb is mostly for shadows glancing at the code, which
> I am not worrying for now (I've totally ignored migration for now).
> Any thoughts any body?

You don't have to understand it very much. Trapping on write faults from
supervisor mode only is fine for normal operation, and you'll have to fault
on everything during live migration (since shadow page tables are built up
via read & write demand faults).

> Also, at present I am not using vtsc, is it worth looking into? some of
> the tsc stuff makes my head spin just like the shadow code does :)...

You have to understand that even less. For pure PV CR4.TSD gets set
appropriately for the VTSC mode. You can hook off that, or duplicate that,
to enable/disable RDTSC exiting instead. You don't have to actually *do* any
vtsc work, as no doubt you jump out of your wrapper code into the proper PV
paths for actually getting any real hypervisor work done (like vtsc).

 -- Keir

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