Re: Xens handling of MCE

[Jan Beulich <jbeulich@xxxxxxxx>]

On 06.09.2023 23:38, Elliott Mitchell wrote:
> On Thu, Aug 31, 2023 at 07:52:05PM +0000, Development wrote:
>>
>>     However, in 2009-02, "cegger" wrote MCA/MCE_in_Xen, a proposal for 
>> having xen start checking the information
>>     Xen started accessing the EDAC information (now called "MCE") at some 
>> point after that, which blocks the linux kernel in dom0 from accessing it.
>>     (I also found what appears to be related sides from a presentation from 
>> 2012 at: 
>> https://lkml.iu.edu/hypermail/linux/kernel/1206.3/01304/xen_vMCE_design_%28v0_2%29.pdf
>>  )
>>
> 
> I hadn't seen that before.  Clearly shows someone who had no idea what
> they were doing designed it.  The author was thinking "virtualize 
> everything!", whereas MCE is a perfect situation for paravirtualization.
> Let Dom0 process MCE events (which allows use of Linux's more up to date
> MCE drivers), then let Dom0 notify Xen if action is needed (a page was
> corrupted, tell the effected domain).
> 
> There was a recent proposal to simply import Linux's rather more recent
> MCE/EDAC source.  This hasn't happened yet.  For people using Xen this
> has been a very concerning issue for some time.

I'm unaware of such a proposal; do you have a reference? EDAC drivers
typically are vendor- or even chipset-specific aiui. At least the latter
wouldn't make them a good fit to import into Xen. Along of what you say
earlier, they instead want to become Xen-aware (to deal with address
translation as necessary). That'll also have better chances of things
staying up-to-date.

Jan