Re: [Xen-devel] Consuming PCI device in PV kernel

[Ian Campbell <Ian.Campbell@xxxxxxxxxx>]

On Fri, 2014-07-25 at 15:30 +0100, Simon Martin wrote:
> Hello Andrew,
> 
> Friday, July 25, 2014, 3:25:35 PM, you wrote:
> 
> > Once you grant map a page from another domain, your domain no longer
> > owns the PTE.  You should either avoid that PTE, or grant unmap the
> > foreign frame first.
> 
> I  have  not  grant mapped this. I have just called update_va_mapping.
> Should I be using grant?

Andrew is saying that the mapping which is currently at the virtual
address is *already* a grant mapping, not that you are trying to grant
map something here. Grant maps need to be unmapped with the grant unmap
hypercall, not just by rewriting the PTE. (IIRC).

You should not be using grants to map PCI IO space, no.

Ian.


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