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.
> 
> You comments and suggestions are welcome!
> Thank you.
> 
> Signed-off-by: Elena Ufimtseva <elena.ufimtseva@xxxxxxxxxx>

Wei,

how about this one for 4.6 then? On one hand I recall you validly
stating that PVH is still unsupported, but otoh the change is well
isolated against affecting anything but PVH, i.e. it is very low risk.

Jan


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