Messages in this thread | | | From | Andrew Cooper <> | Subject | Re: [PATCH v3 0/3] x86/crash: Fix double NMI shootdown bug | Date | Tue, 15 Nov 2022 00:32:24 +0000 |
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On 14/11/2022 23:34, Sean Christopherson wrote: > Tom, > > I Cc'd you this time around because the APM doesn't explicitly state that > GIF is set when EFER.SVME is disabled. KVM's nSVM emulation does set GIF > in this case, but it's not clear whether or not KVM is making up behavior. > If clearing EFER.SVME doesn't set GIF, then patch 1 needs to be modified > to try STGI before clearing EFER.SVME, e.g. if a crash is initiated from > KVM between CLGI and STGI. Responding CPUs are "safe" because GIF=0 also > blocks NMIs, but the initiating CPU might leave GIF=0 when jumping into > the new kernel.
GIF exists independently of EFER.SVME.
It is also gets set by the SKINIT instruction, which is why there is an asymmetry on the #UD conditions of STGI and CLGI.
STGI is also intended to be used by the DLME once critical initialisation is done, hence why it's dependent on EFER.SVME || SKINIT.
~Andrew
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