powerpc/time: Fix clockevent_decrementer initalisation for PR KVM

[ Upstream commit b4d16ab58c41ff0125822464bdff074cebd0fe47 ]

In the recent commit 8b78fdb045de ("powerpc/time: Use
clockevents_register_device(), fixing an issue with large
decrementer") we changed the way we initialise the decrementer
clockevent(s).

We no longer initialise the mult & shift values of
decrementer_clockevent itself.

This has the effect of breaking PR KVM, because it uses those values
in kvmppc_emulate_dec(). The symptom is guest kernels spin forever
mid-way through boot.

For now fix it by assigning back to decrementer_clockevent the mult
and shift values.

Fixes: 8b78fdb045de ("powerpc/time: Use clockevents_register_device(), fixing an issue with large decrementer")
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Signed-off-by: Sasha Levin <sashal@kernel.org>

diff --git a/arch/powerpc/kernel/time.c b/arch/powerpc/kernel/time.c
index 870e75d30459178b37ce52a72c3844dc864b590e..7c7c5a16284d215ed6ffd944a03b08664df7bfe7 100644 (file)
--- a/arch/powerpc/kernel/time.c
+++ b/arch/powerpc/kernel/time.c
@@ -988,6 +988,10 @@ static void register_decrementer_clockevent(int cpu)
 
        printk_once(KERN_DEBUG "clockevent: %s mult[%x] shift[%d] cpu[%d]\n",
                    dec->name, dec->mult, dec->shift, cpu);
+
+       /* Set values for KVM, see kvm_emulate_dec() */
+       decrementer_clockevent.mult = dec->mult;
+       decrementer_clockevent.shift = dec->shift;
 }
 
 static void enable_large_decrementer(void)