Re: [Xen-devel] [PATCH] iommu: leave IOMMU enabled by default during kexec crash transition

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 20.02.19 at 19:19, <igor.druzhinin@xxxxxxxxxx> wrote:
> On 20/02/2019 08:48, Jan Beulich wrote:
>> 
>> Some entity needs to decide whether to add the respective command
>> line option to the crash kernel's command line. It should be this same
>> entity to tell Xen whether to keep the IOMMU enabled while invoking
>> the crash kernel. I am merely guessing that this entity is the kexec
>> tool.
>> 
> 
> I was just double checking and it seems (assuming the device reset
> correctly in the crash kernel) everything seem to work even without
> enabling intel_iommu in the command line - newer kernels handle this
> case by explicitly disabling translation in any case: they expect it to
> be enabled by the previous kernel.

So if they disable translation, how is them doing so any better than us
doing so, other than theirs occurring slightly later on the time scale and
hence there being better chances of in-flight (at the time of the crash)
DMA having completed meanwhile?

Jan



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