From 56548fc0e86cb9156af7a7e1f15ba78f251dafaf Mon Sep 17 00:00:00 2001 From: Paul Mackerras Date: Wed, 3 Dec 2014 14:48:40 +1100 Subject: powerpc/powernv: Return to cpu offline loop when finished in KVM guest When a secondary hardware thread has finished running a KVM guest, we currently put that thread into nap mode using a nap instruction in the KVM code. This changes the code so that instead of doing a nap instruction directly, we instead cause the call to power7_nap() that put the thread into nap mode to return. The reason for doing this is to avoid having the KVM code having to know what low-power mode to put the thread into. In the case of a secondary thread used to run a KVM guest, the thread will be offline from the point of view of the host kernel, and the relevant power7_nap() call is the one in pnv_smp_cpu_disable(). In this case we don't want to clear pending IPIs in the offline loop in that function, since that might cause us to miss the wakeup for the next time the thread needs to run a guest. To tell whether or not to clear the interrupt, we use the SRR1 value returned from power7_nap(), and check if it indicates an external interrupt. We arrange that the return from power7_nap() when we have finished running a guest returns 0, so pending interrupts don't get flushed in that case. Note that it is important a secondary thread that has finished executing in the guest, or that didn't have a guest to run, should not return to power7_nap's caller while the kvm_hstate.hwthread_req flag in the PACA is non-zero, because the return from power7_nap will reenable the MMU, and the MMU might still be in guest context. In this situation we spin at low priority in real mode waiting for hwthread_req to become zero. Signed-off-by: Paul Mackerras Signed-off-by: Michael Ellerman --- arch/powerpc/kernel/exceptions-64s.S | 2 ++ 1 file changed, 2 insertions(+) (limited to 'arch/powerpc/kernel/exceptions-64s.S') diff --git a/arch/powerpc/kernel/exceptions-64s.S b/arch/powerpc/kernel/exceptions-64s.S index 6213f494f40b..db08382e19f1 100644 --- a/arch/powerpc/kernel/exceptions-64s.S +++ b/arch/powerpc/kernel/exceptions-64s.S @@ -131,6 +131,8 @@ BEGIN_FTR_SECTION 1: #endif + /* Return SRR1 from power7_nap() */ + mfspr r3,SPRN_SRR1 beq cr1,2f b power7_wakeup_noloss 2: b power7_wakeup_loss -- cgit v1.2.3