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Re: [Xen-devel] [PATCH 0 of 6] Fix kexec in Xen (take 3)

To: Jan Beulich <JBeulich@xxxxxxxxxx>
Subject: Re: [Xen-devel] [PATCH 0 of 6] Fix kexec in Xen (take 3)
From: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
Date: Wed, 25 May 2011 17:30:53 +0100
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On 25/05/11 17:14, Jan Beulich wrote:
On 25.05.11 at 16:32, Andrew Cooper<andrew.cooper3@xxxxxxxxxx>  wrote:
This set of patches is designed to get the kexec path working again on Xen

kdump kernels can't boot if x2apic mode is enabled and the ACPI tables dont
state this fact.  They also cant boot at all with interrupt remapping

These patches cause xen to track the BSP local APIC boot state and return to
it before kexec'ing to a new kernel.  It also makes sure to disable IO
I was about to reply to the individual patches, but they just seem
too inconsistent to me (comments not matching code, without it
being clear whether code or comment is wrong; functions introduced
that have no callers). Can you work on getting them into a
state suitable for reviewing?
I was splitting the patches up to make them smaller and modular. With the patches as a full series, there are no functions without callers.

Which comments don't match the code?
Further I don't buy your pseudo-quoting of the MP spec saying
that secondary CPUs' local APICs have to be disabled. Keir already
pointed out on your previous submission that in order for them to
receive the INIT and Startup IPIs they must be enabled.
What Keir said and what the MP spec states are in direct contraction. Please do correct me if I have misread/misinterpreted the spec, but:

Section 3.8 states that all local APICs are disabled when the BIOS hands over to the OS.


Section 3.7.3 states that the INIT IPI twiddles the APIC reset lines, which enabled them when they come out of reset, thus receiving and handling the IPI.


One area which is problematic is disabling interrupt remapping.
lapic_suspend() calls iommu_disable_x2apic_IR() which in a previous thread
was deemed to be Intel specific and only works by chance on AMD boxes by
effectivly being a NOP.  As lapic_suspend() is generic code, does this mean
that we can't/don't ever disable interrupt remapping on AMD boxes?

Signed-off-by: Andrew Cooper<andrew.cooper3@xxxxxxxxxx>

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Andrew Cooper - Dom0 Kernel Engineer, Citrix XenServer
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