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

[Andrew Cooper <andrew.cooper3@citrix.com>]

On 25/05/11 17:14, Jan Beulich wrote:
>>>> On 25.05.11 at 16:32, Andrew Cooper<andrew.cooper3@citrix.com>  wrote:
>> This set of patches is designed to get the kexec path working again on Xen
>> 4.x
>>
>> 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
>> enabled.
>>
>> 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
>> virtualisation.
> 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.

and

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.

~Andrew
> Jan
>
>> 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@citrix.com>
>>
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>
>

-- 
Andrew Cooper - Dom0 Kernel Engineer, Citrix XenServer
T: +44 (0)1223 225 900, http://www.citrix.com