[Xen-devel] Re: One question on MMIO

[Tim Deegan <Tim.Deegan@xxxxxxxxxxxxx>]

At 11:27 +0800 on 28 Jun (1183030045), Jiang, Yunhong wrote:
> In sh_page_fault(), there are some code like following, why we think it
> is mmio only when paging_vcpu_mode_translate(v)?

If the vcpu hasn't enabled paging (i.e. !paging_vcpu_mode_translate(v)),
then we shadow the p2m map itself instead of any guest pagetables. 
In that case, MMIO addresses show up as "not present in the guest
table", and are handled earlier on when we test gw.eff_l1e for _PAGE_PRESENT.

Another reason for explicily testing paging_vcpu_mode_translate(v) here
is that if it's not true, then we already have a machine address at this
point, and mmio_space() looks up guest physical addresses.

Cheers,

Tim.

-- 
Tim Deegan <Tim.Deegan@xxxxxxxxxxxxx>, XenSource UK Limited
Registered office c/o EC2Y 5EB, UK; company number 05334508

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