Re: [PATCH] x86/HVM: adjust hvm_interrupt_blocked()

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

On 12/10/18 16:58, Jan Beulich wrote:
> First of all, hvm_intsrc_mce was not considered here at all, yet nothing
> blocks #MC (other than an already in-progress #MC, but dealing with this
> is not the purpose of this patch).

I don't believe we've got sufficient infrastructure to fix this
reasonably yet, but for the record, the real behaviour for MCEs is:

If intel
    broadcast to every thread covered by the MCE bank
else if AMD
    sent to the thread with the lowest id covered by the MCE bank

When trying to inject:

if !CR4.MCE or MCG_STATUS.MCIP
    shutdown

Furthermore, I believe even #MC is blocked by the MOVSS shadow, because
the purpose of the shadow is to indicate "my stack is not safe to take
an exception".

> Additionally STI-shadow only blocks maskable interrupts, but not NMI.

This has been discussed on LKML in the past, but `STI; HLT` will
deadlock if NMIs don't respect the STI shadow.

An NMI which hits that instruction boundary will IRET with IF clear, at
which point the core will halt and never wake up.

I believe the input from the vendor architects was that some very old
cores suffer from this problem, but anything you can get yours hand on
today will respect the STI shadow.

~Andrew

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