[Xen-devel] mce_wrmsr() and (at least) HVM guests

["Jan Beulich" <JBeulich@xxxxxxxxxx>]

With mce_wrmsr() not permitting to write other than all zeroes or all ones
to MCG_CTL and MCn_CTL, it is not possible for guests to implement
workarounds (see the one in mce_cpu_quirks() which has been present in
Linux versions for a very long time). While one could expect PV guests to
be aware of that (and avoid the workaround), HVM guests clearly can't
be expected to. Thus the question is whether the handling should be
made a little more permissive.

Initially I had thought of just making Xen check whether the bit(s) in
question are also off in the physical MSR, but that would imply that
Xen always has implemented at least all of the workarounds any guest
may know of. I'm not sure I have a good other idea, short of allowing
all writes to succeed.

Jan


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