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Re: [Xen-devel] [PATCH v2 2/2] x86/dom0: improve paging memory usage calculations

>>> On 12.12.18 at 10:37, <roger.pau@xxxxxxxxxx> wrote:
> OK, I will iterate over all the devices in order to size the BARs, and
> then add the sum of BARs MMIO regions to the amount of guest memory,
> so that each 1MB of BAR MMIO will require 1 page for the p2m.

Don't you construct a rangeset for all of the BARs already
anyway? For ones which have an address assigned and are
enabled, also taking the address into account would seem
desirable, as then you could do with less than double over-
estimating (in the common case) the amount of space needed.

> Note that ATM I will not account for VF BARs.

Hmm, yes, this is perhaps indeed too much to ask for at this
point. But ultimately we need a clean approach there too.

> OK, so for shadow we also need to account for the IOMMU page table
> size, which is not done now AFAICT.

As said (or perhaps implied) in the other reply, the calculation
there may imply half of the space for the IOMMU, but it may
also mean the other half to be for higher level tables on the
CPU side. It's all guesswork without suitable comments.


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