linux-kernel - [PATCH 3.2 44/70] kvm: x86: only channel 0 of the i8254 is linked to the HPET

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Message-ID: <lsq.1453087115.176877374@decadent.org.uk>
Date:	Mon, 18 Jan 2016 03:18:35 +0000
From:	Ben Hutchings <ben@...adent.org.uk>
To:	linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:	akpm@...ux-foundation.org, "P J P" <pjp@...oraproject.org>,
	"Paolo Bonzini" <pbonzini@...hat.com>
Subject: [PATCH 3.2 44/70] kvm: x86: only channel 0 of the i8254 is linked
 to the HPET

3.2.76-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Paolo Bonzini <pbonzini@...hat.com>

commit e5e57e7a03b1cdcb98e4aed135def2a08cbf3257 upstream.

While setting the KVM PIT counters in 'kvm_pit_load_count', if
'hpet_legacy_start' is set, the function disables the timer on
channel[0], instead of the respective index 'channel'. This is
because channels 1-3 are not linked to the HPET.  Fix the caller
to only activate the special HPET processing for channel 0.

Reported-by: P J P <pjp@...oraproject.org>
Fixes: 0185604c2d82c560dab2f2933a18f797e74ab5a8
Signed-off-by: Paolo Bonzini <pbonzini@...hat.com>
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
 arch/x86/kvm/i8254.c | 1 +
 arch/x86/kvm/x86.c   | 3 ++-
 2 files changed, 3 insertions(+), 1 deletion(-)

--- a/arch/x86/kvm/i8254.c
+++ b/arch/x86/kvm/i8254.c
@@ -437,6 +437,7 @@ void kvm_pit_load_count(struct kvm *kvm,
 	u8 saved_mode;
 	if (hpet_legacy_start) {
 		/* save existing mode for later reenablement */
+		WARN_ON(channel != 0);
 		saved_mode = kvm->arch.vpit->pit_state.channels[0].mode;
 		kvm->arch.vpit->pit_state.channels[0].mode = 0xff; /* disable timer */
 		pit_load_count(kvm, channel, val);
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -3470,7 +3470,8 @@ static int kvm_vm_ioctl_set_pit2(struct
 	       sizeof(kvm->arch.vpit->pit_state.channels));
 	kvm->arch.vpit->pit_state.flags = ps->flags;
 	for (i = 0; i < 3; i++)
-		kvm_pit_load_count(kvm, i, kvm->arch.vpit->pit_state.channels[i].count, start);
+		kvm_pit_load_count(kvm, i, kvm->arch.vpit->pit_state.channels[i].count,
+				   start && i == 0);
 	mutex_unlock(&kvm->arch.vpit->pit_state.lock);
 	return r;
 }