The architecture specifies that when the processor wakes up from a WFE or WFI instruction, the instruction is considered complete, however we currrently return to EL1 (or EL0) at the WFI/WFE instruction itself. While most guests may not be affected by this because their local exception handler performs an exception returning setting the event bit or with an interrupt pending, some guests like UEFI will get wedged due this little mishap. Simply skip the instruction when we have completed the emulation. Cc: Marc Zyngier <marc.zyngier@xxxxxxx> Cc: Ard Biesheuvel <ard.biesheuvel@xxxxxxxxxx> Signed-off-by: Christoffer Dall <christoffer.dall@xxxxxxxxxx> --- Note that I haven't confirmed exactly how Linux guests survives WFI without this fix. My working hypothesis is that the Linux ISR doesn't complete the interrupt, leaving an active interrupt on the LR, which may cause the PE to consider it a wake-up event for the WFI despite the EL1 handler returning to the WFI instruction itself. Tianocore on the other hand may complete the interrupt entirely before returning to the WFI instruction. Input on this is most welcome and likely to improve the quality of my sleep. arch/arm/kvm/handle_exit.c | 2 ++ 1 file changed, 2 insertions(+) diff --git a/arch/arm/kvm/handle_exit.c b/arch/arm/kvm/handle_exit.c index 4c979d4..a96a804 100644 --- a/arch/arm/kvm/handle_exit.c +++ b/arch/arm/kvm/handle_exit.c @@ -93,6 +93,8 @@ static int kvm_handle_wfx(struct kvm_vcpu *vcpu, struct kvm_run *run) else kvm_vcpu_block(vcpu); + kvm_skip_instr(vcpu, kvm_vcpu_trap_il_is32bit(vcpu)); + return 1; } -- 2.0.0 _______________________________________________ kvmarm mailing list kvmarm@xxxxxxxxxxxxxxxxxxxxx https://lists.cs.columbia.edu/mailman/listinfo/kvmarm
