RE: [Xen-devel] [PATCH 0/5] VT-d support for PV guests

["Tian, Kevin" <kevin.tian@xxxxxxxxx>]

>From: Tian, Kevin
>Sent: 2008年5月21日 13:56
>
>>From: Ian Pratt [mailto:Ian.Pratt@xxxxxxxxxxxxx] 
>>Sent: 2008年5月21日 13:32
>>
>>The IOMMU TLB doesn't cache not_present entries, hence you 
>>don't need to
>>do a flush when transitioning an entry from not_present to 
>>present. Some
>>IOMMUs will also re-walk the pagetable if they find a TLB 
>entry that is
>>read-only and the operation is a write, but I can't recall whether VTd
>>is like this.
>
>You're right, though VT-d spec defines a capability bit to indicate
>whether VT-d may cache non-present entry or not. In reality it
>doesn't make sense to do that.
>
>For promotion from non-present to present, then no flush is required.
>But for promotion from read-only to read-write, I guess flush has to
>be forced. Not sure whether currently such grant entry exists to
>switch RO/RW permission on demand.

Forgot above, I'm just talking exact same thing as you already pointed
out. :-P

Thanks,
Kevin

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