Re: [Xen-devel] [PATCH 0/1] ARM: Implement support for write-ctrlreg vm-events

[Tamas K Lengyel <tamas@xxxxxxxxxxxxx>]

On Mon, Mar 7, 2016 at 10:31 AM, Corneliu ZUZU <czuzu@xxxxxxxxxxxxxxx> wrote:

On 3/7/2016 11:12 AM, Tamas K Lengyel wrote:

EPT is not really required for CR3 monitoring, it just has been the case that vm_events have been only implemented for hap-enabled domains.

I suppose this is not valid for vm-events in their entirety, right? I mean it seems to me that @ least for monitor vm-events VMX is enough.

Yes. OTOH I don't think you can find any CPUs on the market today that support VMX but have no EPT so this hasn't really caused any issues for anyone using vm_events, but technically yes VMX is enough for these events.

AFAIK for non-hap case CR3 needs to be trapped unconditionally, yes.

 

If the former is true, shouldn't we do a check like this in vm_event_monitor_get_capabilities instead?

Yes, it should now, this code was just written before vm_event_monitor_get_capabilities was introduced and we haven't gotten around converting this check to it.

Is there any reason why monitor vm-events in their current state wouldn't work on non-hap domains?
If they would work, shouldn't we instead simply move the monitor.write_ctrlreg_enabled part out of the if ( paging_mode_hap(...) ) ?

Yeap, that sounds like the right place to have that check.

 

Tamas

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