[Xen-devel] Requesting for freeze exception for VT-d posted-interrupts

["Wu, Feng" <feng.wu@xxxxxxxxx>]

Hi maintainers,

We would like to request an extension for freeze exception for VT-d 
posted-interrupts patch-set.

1. clarify the state of patch series / feature.
[v3 01/15] Vt-d Posted-interrupt (PI) design
Reviewed-by: Kevin Tian <kevin.tian@xxxxxxxxx>

[v3 02/15] Add helper macro for X86_FEATURE_CX16 feature detection
Reviewed-by: Kevin Tian <kevin.tian@xxxxxxxxx>
Reviewed-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>

[v3 04/15] iommu: Add iommu_intpost to control VT-d Posted-Interrupts feature
Reviewed-by: Kevin Tian <kevin.tian@xxxxxxxxx>

[v3 06/15] vmx: Extend struct pi_desc to support VT-d Posted-Interrupts
Reviewed-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
Acked-by: Kevin Tian <kevin.tian@xxxxxxxxx>

[v3 07/15] vmx: Initialize VT-d Posted-Interrupts Descriptor
Acked-by: Kevin Tian <kevin.tian@xxxxxxxxx>

[v3 09/15] vt-d: Extend struct iremap_entry to support VT-d Posted-Interrupts
Acked-by: Kevin Tian <kevin.tian@xxxxxxxxx>

[v3 10/15] vt-d: Add API to update IRTE when VT-d PI is used
Acked-by: Kevin Tian <kevin.tian@xxxxxxxxx>

[v3 13/15] vmx: Properly handle notification event when vCPU is running
Acked-by: Kevin Tian <kevin.tian@xxxxxxxxx>

[v3 14/15] Update Posted-Interrupts Descriptor during vCPU scheduling
Acked-by: Kevin Tian <kevin.tian@xxxxxxxxx>

[v3 15/15] Add a command line parameter for VT-d posted-interrupts
Reviewed-by: Kevin Tian <kevin.tian@xxxxxxxxx>

2. explain why it needs to be in this release (benefits).
VT-d posted-interrupts is an important interrupt virtualization feature for
device pass-through, the running guest can handle external interrupts
in non-root mode, hence it can eliminate the VM-Exits caused by external
interrupts. Please refer to the design doc:
http://lists.xenproject.org/archives/html/xen-devel/2015-06/msg03691.html

From our experimental environment, after using VT-d posted-interrupts, we
measured 25% improvement in transaction rate netperf TCP_RR benchmark
and 28% reduction in host CPU utilization when using assigned devices.
(10G NIC in my test).

3. explain why it doesn't break things (risks).
This feature only exists in Broadwell Server platform, it has no effect on the
current hardware.

4. CC relevant maintainers and release manager.
Done

There are two main outstanding issues so far:
1. Jan's security concern. I have proposed some solutions but Jan still has
some problems with my proposals. It would be great if Jan can give a clear
proposal so that we can discuss and keep making progress.
2. Scheduler issue: there are conflicts among maintainers Jan/George/Dario.
I would agree with Jan's suggestion below:

" Doing this in a central place is certainly the right approach, but
adding an arch hook that needs to be called everywhere
vcpu_runstate_change() wouldn't serve that purpose. Instead
we'd need to replace all current vcpu_runstate_change() calls
with calls to a new function calling both this and the to be added
arch hook."

However, if different maintainers still hold different opinions, I would 
appreciate
it if maintainers can reach consensus among themselves so that we can keep
making progress

Thanks,
Feng

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