2017-11-10 10:49+0100, Paolo Bonzini: > Sometimes, a processor might execute an instruction while another > processor is updating the page tables for that instruction's code page, > but before the TLB shootdown completes. The interesting case happens > if the page is in the TLB. > > In general, the processor will succeed in executing the instruction and > nothing bad happens. However, what if the instruction is an MMIO access? > If *that* happens, KVM invokes the emulator, and the emulator gets the > updated page tables. If the update side had marked the code page as non > present, the page table walk then will fail and so will x86_decode_insn. > > Unfortunately, even though kvm_fetch_guest_virt is correctly returning > X86EMUL_PROPAGATE_FAULT, x86_decode_insn's caller treats the failure as > a fatal error if the instruction cannot simply be reexecuted (as is the > case for MMIO). And this in fact happened sometimes when rebooting > Windows 2012r2 guests. Just checking ctxt->have_exception and injecting > the exception if true is enough to fix the case. > > Thanks to Eduardo Habkost for helping in the debugging of this issue. > > Reported-by: Yanan Fu <yfu@xxxxxxxxxx> > Cc: Eduardo Habkost <ehabkost@xxxxxxxxxx> > Cc: stable@xxxxxxxxxxxxxxx > Signed-off-by: Paolo Bonzini <pbonzini@xxxxxxxxxx> > --- Applied, thanks.