Re: [Xen-devel] [PATCH v2] x86/boot: enable NMIs after traps init

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 23.10.18 at 16:33, <andrew.cooper3@xxxxxxxxxx> wrote:
> On the subject of having NMIs disabled, it is definitely a more robust
> way of handing off between components.  Until Xen has transitioned the
> BSP and APs into 64bit mode and fully set the IDT up, NMIs are fatal to
> the system.

I don't follow the AP part here - as you say elsewhere on this thread,
IPIs with NMI delivery won't be sent to not fully online CPUs, and
platform originated NMIs ought to go to CPU0, i.e. the BSP.

> Furthermore, I've got some plans to suggest we do this on the kexec path
> as well.  XenServer has one example where we crash from a GPU related
> error, and a slightly delayed NMI arrives, usually when we're in purgatory.

Couldn't we go further an send ourselves an NMI on the BSP (with the
IDT minimally set up so it can be delivered) to disable it until we're ready
to really service it?

Jan



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