[PATCH 1/7] powerpc/kvm: Fix updates of vcpu->cpu on HV KVM

[PATCH 1/7] powerpc/kvm: Fix updates of vcpu->cpu on HV KVM

[Benjamin Herrenschmidt]

This patch removes the powerpc "generic" updates of vcpu->cpu in
load and put, and moves them to the various backends.

The reason is that "HV" KVM does its own sauce with that field
and the generic updates might corrupt it. The field contains the
CPU# of the -first- HW CPU of the core always for all the VCPU
threads of a core (the one that's online from a host Linux
perspective).

However, the preempt notifiers are going to be called on the
threads VCPUs when they are running (due to them sleeping on our
private waitqueue) causing unload to be called, potentially
clobbering the value.

Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
---

This is a bug fix and thus should probably be merged ASAP

 arch/powerpc/kvm/book3s_pr.c |    3 ++-
 arch/powerpc/kvm/booke.c     |    2 ++
 arch/powerpc/kvm/powerpc.c   |    2 --
 3 files changed, 4 insertions(+), 3 deletions(-)

diff --git a/arch/powerpc/kvm/book3s_pr.c b/arch/powerpc/kvm/book3s_pr.c
index a1baec3..9f4c13f 100644
--- a/arch/powerpc/kvm/book3s_pr.c
+++ b/arch/powerpc/kvm/book3s_pr.c
@@ -66,7 +66,7 @@ void kvmppc_core_vcpu_load(struct kvm_vcpu *vcpu, int cpu)
 	svcpu->slb_max = to_book3s(vcpu)->slb_shadow_max;
 	svcpu_put(svcpu);
 #endif
-
+	vcpu->cpu = smp_processor_id();
 #ifdef CONFIG_PPC_BOOK3S_32
 	current->thread.kvm_shadow_vcpu = to_book3s(vcpu)->shadow_vcpu;
 #endif
@@ -86,6 +86,7 @@ void kvmppc_core_vcpu_put(struct kvm_vcpu *vcpu)
 	kvmppc_giveup_ext(vcpu, MSR_FP);
 	kvmppc_giveup_ext(vcpu, MSR_VEC);
 	kvmppc_giveup_ext(vcpu, MSR_VSX);
+	vcpu->cpu = -1;
 }
 
 static void kvmppc_recalc_shadow_msr(struct kvm_vcpu *vcpu)
diff --git a/arch/powerpc/kvm/booke.c b/arch/powerpc/kvm/booke.c
index d25a097..5ecfd80 100644
--- a/arch/powerpc/kvm/booke.c
+++ b/arch/powerpc/kvm/booke.c
@@ -1298,12 +1298,14 @@ void kvmppc_decrementer_func(unsigned long data)
 
 void kvmppc_booke_vcpu_load(struct kvm_vcpu *vcpu, int cpu)
 {
+	vcpu->cpu = smp_processor_id();
 	current->thread.kvm_vcpu = vcpu;
 }
 
 void kvmppc_booke_vcpu_put(struct kvm_vcpu *vcpu)
 {
 	current->thread.kvm_vcpu = NULL;
+	vcpu->cpu = -1;
 }
 
 int __init kvmppc_booke_init(void)
diff --git a/arch/powerpc/kvm/powerpc.c b/arch/powerpc/kvm/powerpc.c
index e7bd630..b54aaa8 100644
--- a/arch/powerpc/kvm/powerpc.c
+++ b/arch/powerpc/kvm/powerpc.c
@@ -411,7 +411,6 @@ void kvm_arch_vcpu_load(struct kvm_vcpu *vcpu, int cpu)
 	mtspr(SPRN_VRSAVE, vcpu->arch.vrsave);
 #endif
 	kvmppc_core_vcpu_load(vcpu, cpu);
-	vcpu->cpu = smp_processor_id();
 }
 
 void kvm_arch_vcpu_put(struct kvm_vcpu *vcpu)
@@ -420,7 +419,6 @@ void kvm_arch_vcpu_put(struct kvm_vcpu *vcpu)
 #ifdef CONFIG_BOOKE
 	vcpu->arch.vrsave = mfspr(SPRN_VRSAVE);
 #endif
-	vcpu->cpu = -1;
 }
 
 int kvm_arch_vcpu_ioctl_set_guest_debug(struct kvm_vcpu *vcpu,

Re: [PATCH 1/7] powerpc/kvm: Fix updates of vcpu->cpu on HV KVM

[Paul Mackerras]

On Fri, Aug 17, 2012 at 06:38:03PM +1000, Benjamin Herrenschmidt wrote:
> This patch removes the powerpc "generic" updates of vcpu->cpu in
> load and put, and moves them to the various backends.
> 
> The reason is that "HV" KVM does its own sauce with that field
> and the generic updates might corrupt it. The field contains the
> CPU# of the -first- HW CPU of the core always for all the VCPU
> threads of a core (the one that's online from a host Linux
> perspective).
> 
> However, the preempt notifiers are going to be called on the
> threads VCPUs when they are running (due to them sleeping on our
> private waitqueue) causing unload to be called, potentially
> clobbering the value.
> 
> Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>

Acked-by: Paul Mackerras <paulus@samba.org>