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

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

> From: Jan Beulich [mailto:JBeulich@xxxxxxxx]
> Sent: Thursday, August 14, 2014 4:12 PM
> 
> >>> On 15.08.14 at 00:53, <kevin.tian@xxxxxxxxx> wrote:
> > btw just curious how we handle p2m_ram_ro today. Does it play any trick
> > to fail-safe in IOMMU side, e.g. zap the mapping or not? Otherwise when
> > it allows read-only DMA there's no way to prevent DMA writes either. :-)
> 
> Why would that be? A page marked r/o in the IOMMU page tables
> ought to very well be protected against DMA writes. It's just that
> these will cause faults, which - if happening too frequently - will
> result in the device getting turned off, quite likely (implicitly) killing
> the guest.
> 

yes, as protection it's enough, and it's only a problem for emulation. sorry
for messed msg after a long discussion thread. :/

Thanks
Kevin

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