kvm: x86: Save/restore FPU OP, IP and DP
These FPU states are properly maintained by KVM but not yet by TCG. So far we unconditionally set them to 0 in the guest which may cause state corruptions, though not with modern guests. To avoid breaking backward migration, use a conditional subsection that is only written if any of the three fields is non-zero. The guest's FNINIT clears them frequently, and cleared IA32_MISC_ENABLE MSR[2] reduces the probability of non-zero values further so that this subsection is not expected to restrict migration in any common scenario. Signed-off-by: NJan Kiszka <jan.kiszka@siemens.com> Signed-off-by: NAvi Kivity <avi@redhat.com>
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