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Re: [Xen-devel] [PATCH v1 0/2] Extend ioreq-server to support page write protection

> -----Original Message-----
> From: Jan Beulich [mailto:JBeulich@xxxxxxxx]
> Sent: Monday, July 28, 2014 4:25 PM
> To: Ye, Wei
> Cc: ian.campbell@xxxxxxxxxx; Paul.Durrant@xxxxxxxxxx;
> ian.jackson@xxxxxxxxxxxxx; stefano.stabellini@xxxxxxxxxxxxx; xen-
> devel@xxxxxxxxxxxxx; keir@xxxxxxx
> Subject: Re: [PATCH v1 0/2] Extend ioreq-server to support page write
> protection
> >>> On 28.07.14 at 19:55, <wei.ye@xxxxxxxxx> wrote:
> > ioreq-server is proposed to forward PIO and MMIO request to multiple
> > device models according to the io range. XenGT (Intel Graphics
> > Virtualization technology, please refer to
> > https://01.org/xen/blogs/srclarkx/2013/graphics-virtualization-
> > xengt) driver reside in Dom0 as a virtual graphics device model also
> > need to trap and emulate the guest's write operation to some specific
> > memory pages, like the memory pages used by guest graphics driver as
> > PPGTT(per-process graphics translation table). We add an new p2m type
> > "p2m_ram_wp" to trap the page write operation. Page of this new p2m
> > type is read only and for write, the request will go to device model
> > via ioreq-server.
> So how is this write-protection supposed to work on the IOMMU side when
> sharing page tables?

Thanks for pointing out this question. Write-protection is not supposed to work 
when sharing page tables between EPT and vt-d.
An explicit command line "iommu=no-sharept" should be setted for avoiding 
undesirable iommu fault.

> Jan

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