linux-kernel - [PATCH 3.12 01/63] KVM: ARM: Fix calculation of virtual CPU ID

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Date:	Thu, 30 Apr 2015 14:11:30 +0200
From:	Jiri Slaby <jslaby@...e.cz>
To:	stable@...r.kernel.org
Cc:	linux-kernel@...r.kernel.org,
	Jonathan Austin <jonathan.austin@....com>,
	Christoffer Dall <christoffer.dall@...aro.org>,
	Shannon Zhao <shannon.zhao@...aro.org>,
	Jiri Slaby <jslaby@...e.cz>
Subject: [PATCH 3.12 01/63] KVM: ARM: Fix calculation of virtual CPU ID

From: Jonathan Austin <jonathan.austin@....com>

3.12-stable review patch.  If anyone has any objections, please let me know.

===============

commit 1158fca401e09665c440a9fe4fd4f131ee85c13b upstream.

KVM does not have a notion of multiple clusters for CPUs, just a linear
array of CPUs. When using a system with cores in more than one cluster, the
current method for calculating the virtual MPIDR will leak the (physical)
cluster information into the virtual MPIDR. One effect of this is that
Linux under KVM fails to boot multiple CPUs that aren't in the 0th cluster.

This patch does away with exposing the real MPIDR fields in favour of simply
using the virtual CPU number (but preserving the U bit, as before).

Signed-off-by: Jonathan Austin <jonathan.austin@....com>
Acked-by: Marc Zyngier <marc.zyngier@....com>
Signed-off-by: Christoffer Dall <christoffer.dall@...aro.org>
Signed-off-by: Shannon Zhao <shannon.zhao@...aro.org>
Signed-off-by: Jiri Slaby <jslaby@...e.cz>
---
 arch/arm/kvm/coproc_a15.c | 11 ++++-------
 1 file changed, 4 insertions(+), 7 deletions(-)

diff --git a/arch/arm/kvm/coproc_a15.c b/arch/arm/kvm/coproc_a15.c
index cf93472b9dd6..bbd4b888dbf3 100644
--- a/arch/arm/kvm/coproc_a15.c
+++ b/arch/arm/kvm/coproc_a15.c
@@ -27,14 +27,11 @@
 static void reset_mpidr(struct kvm_vcpu *vcpu, const struct coproc_reg *r)
 {
 	/*
-	 * Compute guest MPIDR:
-	 * (Even if we present only one VCPU to the guest on an SMP
-	 * host we don't set the U bit in the MPIDR, or vice versa, as
-	 * revealing the underlying hardware properties is likely to
-	 * be the best choice).
+	 * Compute guest MPIDR. No need to mess around with different clusters
+	 * but we read the 'U' bit from the underlying hardware directly.
 	 */
-	vcpu->arch.cp15[c0_MPIDR] = (read_cpuid_mpidr() & ~MPIDR_LEVEL_MASK)
-		| (vcpu->vcpu_id & MPIDR_LEVEL_MASK);
+	vcpu->arch.cp15[c0_MPIDR] = (read_cpuid_mpidr() & MPIDR_SMP_BITMASK)
+					| vcpu->vcpu_id;
 }
 
 #include "coproc.h"
-- 
2.3.5

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