On 06/09/18 10:16, Paul Durrant wrote:
>> -----Original Message-----
>> From: Andrew Cooper [mailto:[email protected]]
>> Sent: 05 September 2018 19:12
>> To: Xen-devel <[email protected]>
>> Cc: Andrew Cooper <[email protected]>; Jan Beulich
>> <[email protected]>; Wei Liu <[email protected]>; Roger Pau Monne
>> <[email protected]>; Paul Durrant <[email protected]>; Stefano
>> Stabellini <[email protected]>; Julien Grall <[email protected]>
>> 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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