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xen-devel
Re: [Xen-devel] [PATCH] Fixing ATS enabling for device assignment
Jan Beulich wrote:
Weidong Han 05/19/10 11:12 AM >>>
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.
Perhaps I didn't express my concern properly: It's not really the hypervisor
depending on anything done by the tools, but the code you ad to the hypervisor
will trun out pointless if the tools move FLR past the point where
domain_context_mapping() gets executed.
Yes, it's a problem in your case. But FLR is required to be earlier than
domain_context_mapping for device assignment.
It would seem more clean to me if e.g. the tools re-enabled ATS after doing
FLR if it was enabled before.I
Sounds good. But i'm not sure if it's suitable or easy to maintain
capability enabling/disabling in control panel, I feel current device
handling logic (hotplug, assign/deassign, PV and hvm) in control panel
is a bit of complex.
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.
That's fine, but doesn't answer my question.
if not disable it after de-assignment, enable_ats_device will add the
device multiple times to ats_devices list.
Regards,
Weidong
Jan
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