linux-kernel - RE: pstore does not work under xen

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Date:   Thu, 19 Sep 2019 15:51:33 +0000
From:   "Luck, Tony" <tony.luck@...el.com>
To:     James Dingwall <james@...gwall.me.uk>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
CC:     Kees Cook <keescook@...omium.org>,
        Anton Vorontsov <anton@...msg.org>,
        Colin Cross <ccross@...roid.com>,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        Juergen Gross <jgross@...e.com>
Subject: RE: pstore does not work under xen

> I have been investigating a regression in our environment where pstore 
> (efi-pstore specifically but I suspect this would affect all 
> implementations) no longer works after upgrading from a 4.4 to 5.0 
> kernel when running under xen.  (This is an Ubuntu kernel but I don't 
> think there are patches which affect this area.)

I don't have any answer for this ... but want to throw out the idea that
VMM systems could provide some hypercalls to guests to save/return
some blob of memory (perhaps the "save" triggers automagically if the
guest crashes?).

That would provide a much better pstore back end than relying on emulation
of EFI persistent variables (which have severe contraints on size, and don't
support some pstore modes because you can't dynamically update EFI variables
hundreds of times per second).

-Tony