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Re: [Xen-devel] [PATCH] Fixing ATS enabling for device assignment

>>> "Han, Weidong"  05/19/10 4:37 AM >>>
>Currently, Xen only enables ATS in Xen booting. When a ATS capable device is 
>assigned to guest, ATS is actually not enabled because FLR before assignment 
>causes it to be disabled. Thus ATS cannot be used in guest. This patch enables 
>ATS in domain_context_mapping. This ensures ATS is enabled in assignment 
>because FLR is earlier than domain_context_mapping call. Therefore ATS can be 
>used in guest. This patch also implements disable_ats_device to disable ATS 
>when the device is deassigned from a domain.

Hmm, this looks inconsistent to me: Iirc FLR is being done from the tools, so 
unless it is technically impossible to do FLR after domain_context_mapping(), 
the patch creates a hypervisor dependency on the tools (if nothing else, a 
latent bug - to be introduced the moment operation ordering changes in the 

Further, if ATS gets enabled at boot time, why would you want to disable it 
after de-assignment?

Finally (only partially related) - why are {en,dis}able_ats_device() 
architecture specific? PCI config space accesses really aren't I would think.


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