RE: [PATCH] AMD/IOMMU: correct shattering of super pages

[Paul Durrant <xadimgnik@xxxxxxxxx>]

> -----Original Message-----
> From: Jan Beulich <jbeulich@xxxxxxxx>
> Sent: 20 October 2020 14:54
> To: xen-devel@xxxxxxxxxxxxxxxxxxxx
> Cc: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>; Paul Durrant <paul@xxxxxxx>
> Subject: [PATCH] AMD/IOMMU: correct shattering of super pages
> 
> Fill the new page table _before_ installing into a live page table
> hierarchy, as installing a blank page first risks I/O faults on
> sub-ranges of the original super page which aren't part of the range
> for which mappings are being updated.
> 
> While at it also do away with mapping and unmapping the same fresh
> intermediate page table page once per entry to be written.
> 
> Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
> ---
> Afaict this corrects presently dead code: I don't think there are ways
> for super pages to be created in the first place, i.e. none could ever
> need shattering.

I believe you are correct, yes. Certainly an improvement though so...

Reviewed-by: Paul Durrant <paul@xxxxxxx>