linux-kernel - [PATCH AUTOSEL 4.14 114/115] powerpc/time: Fix clockevent

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Date:   Tue, 12 Nov 2019 20:56:21 -0500
From:   Sasha Levin <sashal@...nel.org>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
Cc:     Michael Ellerman <mpe@...erman.id.au>,
        Sasha Levin <sashal@...nel.org>, linuxppc-dev@...ts.ozlabs.org
Subject: [PATCH AUTOSEL 4.14 114/115] powerpc/time: Fix clockevent_decrementer initalisation for PR KVM

From: Michael Ellerman <mpe@...erman.id.au>

[ 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@...erman.id.au>
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 arch/powerpc/kernel/time.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/arch/powerpc/kernel/time.c b/arch/powerpc/kernel/time.c
index 870e75d304591..7c7c5a16284d2 100644
--- 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)
-- 
2.20.1