Re: [Xen-devel] [PATCH v2] PVH Dom0 RMRR IOMMU mapping regression fix

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 25.09.15 at 22:59, <elena.ufimtseva@xxxxxxxxxx> wrote:
> From: Elena Ufimtseva <elena.ufimtseva@xxxxxxxxxx>
> 
> This patch addresses a regression introduced by commit 
> 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 Dom0 PVH 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.
> 
> As was mentioned in the earlier discussion, the PVH Dom0 construction code
> should be modified to properly map RMRR regions in IOMMU. Since change will 
> be
> too invasive, this solution is a temporary fix at this time before better
> solution is in. Also as Jan mentioned, there is no need in having 'x' 
> permissions
> for p2m entry of a mmio region, thus changed here.

Well, now that I look at this again I think there could be reasons for
execute permission to be needed: Code placed in ROM may require
this. But then again Dom0 shouldn't on its own (i.e. without
involving the hypervisor) invoke such code, which usually would be
expecting to be run in root mode ring 0 anyway. So I think not
defaulting to include X is the right thing. Hence ...

> Signed-off-by: Elena Ufimtseva <elena.ufimtseva@xxxxxxxxxx>

Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>


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