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KVM: PPC: Book3S HV: Read kvm->arch.emul_smt_mode under kvm->lock 

Commit 1e175d2 ("KVM: PPC: Book3S HV: Pack VCORE IDs to access full
VCPU ID space", 2018-07-25) added code that uses kvm->arch.emul_smt_mode
before any VCPUs are created.  However, userspace can change
kvm->arch.emul_smt_mode at any time up until the first VCPU is created.
Hence it is (theoretically) possible for the check in
kvmppc_core_vcpu_create_hv() to race with another userspace thread
changing kvm->arch.emul_smt_mode.

This fixes it by moving the test that uses kvm->arch.emul_smt_mode into
the block where kvm->lock is held.

Signed-off-by: Paul Mackerras <paulus@ozlabs.org>
This commit is contained in:
Paul Mackerras 2018-07-26 15:38:41 +10:00
parent 1ebe6b81eb
commit b5c6f7607b
1 changed files with 8 additions and 9 deletions
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17
arch/powerpc/kvm/book3s_hv.c
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@ -1989,16 +1989,10 @@ static struct kvm_vcpu *kvmppc_core_vcpu_create_hv(struct kvm *kvm,
unsigned int id)
{
struct kvm_vcpu *vcpu;
int err = -EINVAL;
int err;
int core;
struct kvmppc_vcore *vcore;
if (id >= (KVM_MAX_VCPUS * kvm->arch.emul_smt_mode) &&
cpu_has_feature(CPU_FTR_ARCH_300)) {
pr_devel("DNCI: VCPU ID too high\n");
goto out;
}
err = -ENOMEM;
vcpu = kmem_cache_zalloc(kvm_vcpu_cache, GFP_KERNEL);
if (!vcpu)
@ -2055,8 +2049,13 @@ static struct kvm_vcpu *kvmppc_core_vcpu_create_hv(struct kvm *kvm,
vcore = NULL;
err = -EINVAL;
if (cpu_has_feature(CPU_FTR_ARCH_300)) {
BUG_ON(kvm->arch.smt_mode != 1);
core = kvmppc_pack_vcpu_id(kvm, id);
if (id >= (KVM_MAX_VCPUS * kvm->arch.emul_smt_mode)) {
pr_devel("KVM: VCPU ID too high\n");
core = KVM_MAX_VCORES;
} else {
BUG_ON(kvm->arch.smt_mode != 1);
core = kvmppc_pack_vcpu_id(kvm, id);
}
} else {
core = id / kvm->arch.smt_mode;
}