queue-4.19/kvm-ppc-book3s-hv-don-t-take-kvm-lock-around-kvm_for.patch

   1 From fd4151f889375be570c9058b5492269b1cf7f94d Mon Sep 17 00:00:00 2001
   2 From: Paul Mackerras <paulus@ozlabs.org>
   3 Date: Thu, 23 May 2019 16:36:32 +1000
   4 Subject: KVM: PPC: Book3S HV: Don't take kvm->lock around kvm_for_each_vcpu
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   8
   9 [ Upstream commit 5a3f49364c3ffa1107bd88f8292406e98c5d206c ]
  10
  11 Currently the HV KVM code takes the kvm->lock around calls to
  12 kvm_for_each_vcpu() and kvm_get_vcpu_by_id() (which can call
  13 kvm_for_each_vcpu() internally).  However, that leads to a lock
  14 order inversion problem, because these are called in contexts where
  15 the vcpu mutex is held, but the vcpu mutexes nest within kvm->lock
  16 according to Documentation/virtual/kvm/locking.txt.  Hence there
  17 is a possibility of deadlock.
  18
  19 To fix this, we simply don't take the kvm->lock mutex around these
  20 calls.  This is safe because the implementations of kvm_for_each_vcpu()
  21 and kvm_get_vcpu_by_id() have been designed to be able to be called
  22 locklessly.
  23
  24 Signed-off-by: Paul Mackerras <paulus@ozlabs.org>
  25 Reviewed-by: Cédric Le Goater <clg@kaod.org>
  26 Signed-off-by: Paul Mackerras <paulus@ozlabs.org>
  27 Signed-off-by: Sasha Levin <sashal@kernel.org>
  28 ---
  29  arch/powerpc/kvm/book3s_hv.c | 9 +--------
  30  1 file changed, 1 insertion(+), 8 deletions(-)
  31
  32 diff --git a/arch/powerpc/kvm/book3s_hv.c b/arch/powerpc/kvm/book3s_hv.c
  33 index 3e3a71594e63..083dcedba11c 100644
  34 --- a/arch/powerpc/kvm/book3s_hv.c
  35 +++ b/arch/powerpc/kvm/book3s_hv.c
  36 @@ -426,12 +426,7 @@ static void kvmppc_dump_regs(struct kvm_vcpu *vcpu)
  37
  38  static struct kvm_vcpu *kvmppc_find_vcpu(struct kvm *kvm, int id)
  39  {
  40 -       struct kvm_vcpu *ret;
  41 -
  42 -       mutex_lock(&kvm->lock);
  43 -       ret = kvm_get_vcpu_by_id(kvm, id);
  44 -       mutex_unlock(&kvm->lock);
  45 -       return ret;
  46 +       return kvm_get_vcpu_by_id(kvm, id);
  47  }
  48
  49  static void init_vpa(struct kvm_vcpu *vcpu, struct lppaca *vpa)
  50 @@ -1309,7 +1304,6 @@ static void kvmppc_set_lpcr(struct kvm_vcpu *vcpu, u64 new_lpcr,
  51         struct kvmppc_vcore *vc = vcpu->arch.vcore;
  52         u64 mask;
  53
  54 -       mutex_lock(&kvm->lock);
  55         spin_lock(&vc->lock);
  56         /*
  57          * If ILE (interrupt little-endian) has changed, update the
  58 @@ -1349,7 +1343,6 @@ static void kvmppc_set_lpcr(struct kvm_vcpu *vcpu, u64 new_lpcr,
  59                 mask &= 0xFFFFFFFF;
  60         vc->lpcr = (vc->lpcr & ~mask) | (new_lpcr & mask);
  61         spin_unlock(&vc->lock);
  62 -       mutex_unlock(&kvm->lock);
  63  }
  64
  65  static int kvmppc_get_one_reg_hv(struct kvm_vcpu *vcpu, u64 id,
  66 --
  67 2.20.1
  68