On 04.06.2020 09:49, Paul Durrant wrote:
>> -----Original Message-----
>> From: Igor Druzhinin <igor.druzhi...@citrix.com>
>> Sent: 03 June 2020 23:42
>> To: xen-devel@lists.xenproject.org
>> Cc: jbeul...@suse.com; andrew.coop...@citrix.com; w...@xen.org;
>> roger....@citrix.com;
>> george.dun...@citrix.com; p...@xen.org; Igor Druzhinin
>> <igor.druzhi...@citrix.com>
>> Subject: [PATCH for-4.14 v3] x86/svm: do not try to handle recalc NPT faults
>> immediately
>>
>> A recalculation NPT fault doesn't always require additional handling
>> in hvm_hap_nested_page_fault(), moreover in general case if there is no
>> explicit handling done there - the fault is wrongly considered fatal.
>>
>> This covers a specific case of migration with vGPU assigned which
>> uses direct MMIO mappings made by XEN_DOMCTL_memory_mapping hypercall:
>> at a moment log-dirty is enabled globally, recalculation is requested
>> for the whole guest memory including those mapped MMIO regions
>
> I still think it is odd to put this in the commit comment since, as I
> said before, Xen ensures that this situation cannot happen at
> the moment.
Aiui Igor had replaced reference to passed-through devices by reference
to mere handing of an MMIO range to a guest. Are you saying we suppress
log-dirty enabling in this case as well? I didn't think we do:
if ( has_arch_pdevs(d) && log_global )
{
/*
* Refuse to turn on global log-dirty mode
* if the domain is sharing the P2M with the IOMMU.
*/
return -EINVAL;
}
Seeing this code I wonder about the non-sharing case: If what the
comment says was true, the condition would need to change, but I
think it's the comment which is wrong, and we don't want global
log-dirty as long as an IOMMU is in use at all for a domain.
Jan
