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xen-devel
Re: [Xen-devel] [PATCH] Fixing ATS enabling for device assignment
Jan Beulich wrote:
"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
tools).
It doesn't depend on FLR from tools. It just ensures ATS is enabled for
device assignment in guest. If ATS is already enabled, enable_ats_device
won't re-enable it.
Further, if ATS gets enabled at boot time, why would you want to disable it
after de-assignment?
ATS enabled devices will be added to ats_devices list. disabling ATS
will remove a device from that list and avoid leak. If ATS is enabled on
a VF, and it's destroyed by removing PF driver, disable_ats_device will
be invoked to remove it from the list.
Regards,
Weidong
Finally (only partially related) - why are {en,dis}able_ats_device()
architecture specific? PCI config space accesses really aren't I would think
Jan
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