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Re: [Xen-devel] [PATCH 3/5] x86/hvm: Make HVM_PARAM_{STORE, CONSOLE}_EVTCHN read-only to the guest
- To: Paul Durrant <Paul.Durrant@xxxxxxxxxx>, Xen-devel <xen-devel@xxxxxxxxxxxxx>
- From: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
- Date: Thu, 6 Sep 2018 16:29:30 +0100
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- Cc: Julien Grall <julien.grall@xxxxxxx>, Stefano Stabellini <sstabellini@xxxxxxxxxx>, Wei Liu <wei.liu2@xxxxxxxxxx>, Jan Beulich <JBeulich@xxxxxxxx>, Roger Pau Monne <roger.pau@xxxxxxxxxx>
- Delivery-date: Thu, 06 Sep 2018 15:29:38 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
- Openpgp: preference=signencrypt
On 06/09/18 10:16, Paul Durrant wrote:
>> -----Original Message-----
>> From: Andrew Cooper [mailto:andrew.cooper3@xxxxxxxxxx]
>> Sent: 05 September 2018 19:12
>> To: Xen-devel <xen-devel@xxxxxxxxxxxxx>
>> Cc: Andrew Cooper <Andrew.Cooper3@xxxxxxxxxx>; Jan Beulich
>> <JBeulich@xxxxxxxx>; Wei Liu <wei.liu2@xxxxxxxxxx>; Roger Pau Monne
>> <roger.pau@xxxxxxxxxx>; Paul Durrant <Paul.Durrant@xxxxxxxxxx>; Stefano
>> Stabellini <sstabellini@xxxxxxxxxx>; Julien Grall <julien.grall@xxxxxxx>
>> Subject: [PATCH 3/5] x86/hvm: Make
>> HVM_PARAM_{STORE,CONSOLE}_EVTCHN read-only to the guest
>>
>> These values are set by the toolstack for each create/restore operation, and
>> bound by xen{store,console}d before the the guest starts running.
>>
>> A guest has no reason to modify them at all, and the matching *_PFN
>> parameters
>> are already read-only. Adjust the *_EVTCHN permissions to be consistent.
> Unfortunately this patch will break the Windows PV driver function here:
>
> http://xenbits.xen.org/gitweb/?p=pvdrivers/win/xenbus.git;a=blob;f=src/xenbus/evtchn.c;hb=HEAD#l1037
>
> Unfortunately the values really do change across a reset. It would be
> possible to use volatile (disappear on reboot) registry keys to store the
> updated values instead but I don't really see any harm in allowing the guest
> to update the values to be correct, unless we want to change Xen to do the
> job so the guest doesn't have to go through this dance.
:( Everything is terrible.
This is a general problem, not x86 specific, so I'll drop this patch and
make a similar adjustment to the ARM one.
~Andrew
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