Re: [Xen-devel] Regression in RMRRs identity mapping for PVH Dom0

[Elena Ufimtseva <elena.ufimtseva@xxxxxxxxxx>]

On Thu, Sep 24, 2015 at 11:29:54AM +0100, Wei Liu wrote:
> Hi Elena
> 
> On Wed, Sep 23, 2015 at 11:56:12AM -0400, Elena Ufimtseva wrote:
> > Hi                                                                          
> >     
> >                                                                             
> >     
> > There is a regression in RMRR patch 
> > 5ae03990c120a7b3067a52d9784c9aa72c0705a6 in
> > new set_identity_p2m_entry. RMRRs are not being mapped in IOMMU for PVH 
> > Dom0.
> > This causes pages faults and some long 'hang-like' delays during boot and
> > device assignments.
> >                                                                             
> >     
> > During construct_dom0, in PVH path  p2m is being constructed and identity 
> > mapped
> > in IOMMU. The p2m type is p2m_mmio_direct and p2m access p2m_rwx.
> > New code used to map RMRRs invoked from rmrr_identity_mapping               
> >     
> > checks if p2m entry exists with same type and access and if yes, skips iommu
> > mapping. Since there are p2m entries for pvh dom0 iomem, RMRRs are not being
> > mapped in IOMMU.
> >                                                                             
> >     
> > This debug patch attached fixes this and Ill be glad to see if there is a 
> > more elegant fix.
> >                                                                             
> >     
> 
> From a release point of view, PVH Dom0 is not officially supported so I
> don't consider this issue a blocker.
> 
Understand.

> We can backport the proper fix to 4.6.1 if necessary, but I doubt this
> is the only fix we need to make PVH Dom0 work on 4.6. Am I right?

Dom0 PVH boots with some glitches on Intel platforms and with some others on
AMD and it will see for sure more patches. But this problem will
make Dom0 on some Intel platforms to hang, throw page faults or may not be able
to boot at all (as I have seend that happening for some devices when
doing work on extra RMRRs).
> 
> Wei.

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