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

[Tim Deegan <tim@xxxxxxx>]

At 15:17 +0800 on 24 Sep (1443107852), Chen, Tiejun wrote:
> On 9/23/2015 11:56 PM, 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.
> 
> Based on your explanation, sounds pvh always creates this mapping 
> beforehand, so what about this?
> 
> diff --git a/xen/arch/x86/mm/p2m.c b/xen/arch/x86/mm/p2m.c
> index cf8485e..d026845 100644
> --- a/xen/arch/x86/mm/p2m.c
> +++ b/xen/arch/x86/mm/p2m.c
> @@ -964,7 +964,7 @@ int set_identity_p2m_entry(struct domain *d, 
> unsigned long gfn,
>       struct p2m_domain *p2m = p2m_get_hostp2m(d);
>       int ret;
> 
> -    if ( !paging_mode_translate(p2m->domain) )
> +    if ( !paging_mode_translate(p2m->domain) || is_pvh_domain(d) )

Sorry, but that wouldn't be safe. :(  PVH domains need the same
protection as any other paging_mode_translate ones.

AIUI the problem is that before the call to set_identity_p2m_entry(),
PVH dom0 has a p2m entry covering this range but no IOMMU entry.  Is
that right?  So the fix will be to make PVH dom0 construction set up
the IOMMU correctly when it sets up the p2m.

Cheers,

Tim.

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