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KVM: PPC: Book3S HV: Use new mutex to synchronize MMU setup
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Currently the HV KVM code uses kvm->lock in conjunction with a flag,
kvm->arch.mmu_ready, to synchronize MMU setup and hold off vcpu
execution until the MMU-related data structures are ready.  However,
this means that kvm->lock is being taken inside vcpu->mutex, which
is contrary to Documentation/virtual/kvm/locking.txt and results in
lockdep warnings.

To fix this, we add a new mutex, kvm->arch.mmu_setup_lock, which nests
inside the vcpu mutexes, and is taken in the places where kvm->lock
was taken that are related to MMU setup.

Additionally we take the new mutex in the vcpu creation code at the
point where we are creating a new vcore, in order to provide mutual
exclusion with kvmppc_update_lpcr() and ensure that an update to
kvm->arch.lpcr doesn't get missed, which could otherwise lead to a
stale vcore->lpcr value.

Signed-off-by: Paul Mackerras <paulus@ozlabs.org>
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Paul Mackerras committed May 29, 2019
1 parent c395fe1 commit 0d4ee88
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Showing 3 changed files with 42 additions and 26 deletions.
1 change: 1 addition & 0 deletions arch/powerpc/include/asm/kvm_host.h
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Original file line number Diff line number Diff line change
Expand Up @@ -325,6 +325,7 @@ struct kvm_arch {
#endif
struct kvmppc_ops *kvm_ops;
#ifdef CONFIG_KVM_BOOK3S_HV_POSSIBLE
struct mutex mmu_setup_lock; /* nests inside vcpu mutexes */
u64 l1_ptcr;
int max_nested_lpid;
struct kvm_nested_guest *nested_guests[KVM_MAX_NESTED_GUESTS];
Expand Down
36 changes: 18 additions & 18 deletions arch/powerpc/kvm/book3s_64_mmu_hv.c
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Original file line number Diff line number Diff line change
Expand Up @@ -63,7 +63,7 @@ struct kvm_resize_hpt {
struct work_struct work;
u32 order;

/* These fields protected by kvm->lock */
/* These fields protected by kvm->arch.mmu_setup_lock */

/* Possible values and their usage:
* <0 an error occurred during allocation,
Expand All @@ -73,7 +73,7 @@ struct kvm_resize_hpt {
int error;

/* Private to the work thread, until error != -EBUSY,
* then protected by kvm->lock.
* then protected by kvm->arch.mmu_setup_lock.
*/
struct kvm_hpt_info hpt;
};
Expand Down Expand Up @@ -139,7 +139,7 @@ long kvmppc_alloc_reset_hpt(struct kvm *kvm, int order)
long err = -EBUSY;
struct kvm_hpt_info info;

mutex_lock(&kvm->lock);
mutex_lock(&kvm->arch.mmu_setup_lock);
if (kvm->arch.mmu_ready) {
kvm->arch.mmu_ready = 0;
/* order mmu_ready vs. vcpus_running */
Expand Down Expand Up @@ -183,7 +183,7 @@ long kvmppc_alloc_reset_hpt(struct kvm *kvm, int order)
/* Ensure that each vcpu will flush its TLB on next entry. */
cpumask_setall(&kvm->arch.need_tlb_flush);

mutex_unlock(&kvm->lock);
mutex_unlock(&kvm->arch.mmu_setup_lock);
return err;
}

Expand Down Expand Up @@ -1447,7 +1447,7 @@ static void resize_hpt_pivot(struct kvm_resize_hpt *resize)

static void resize_hpt_release(struct kvm *kvm, struct kvm_resize_hpt *resize)
{
if (WARN_ON(!mutex_is_locked(&kvm->lock)))
if (WARN_ON(!mutex_is_locked(&kvm->arch.mmu_setup_lock)))
return;

if (!resize)
Expand All @@ -1474,14 +1474,14 @@ static void resize_hpt_prepare_work(struct work_struct *work)
if (WARN_ON(resize->error != -EBUSY))
return;

mutex_lock(&kvm->lock);
mutex_lock(&kvm->arch.mmu_setup_lock);

/* Request is still current? */
if (kvm->arch.resize_hpt == resize) {
/* We may request large allocations here:
* do not sleep with kvm->lock held for a while.
* do not sleep with kvm->arch.mmu_setup_lock held for a while.
*/
mutex_unlock(&kvm->lock);
mutex_unlock(&kvm->arch.mmu_setup_lock);

resize_hpt_debug(resize, "resize_hpt_prepare_work(): order = %d\n",
resize->order);
Expand All @@ -1494,9 +1494,9 @@ static void resize_hpt_prepare_work(struct work_struct *work)
if (WARN_ON(err == -EBUSY))
err = -EINPROGRESS;

mutex_lock(&kvm->lock);
mutex_lock(&kvm->arch.mmu_setup_lock);
/* It is possible that kvm->arch.resize_hpt != resize
* after we grab kvm->lock again.
* after we grab kvm->arch.mmu_setup_lock again.
*/
}

Expand All @@ -1505,7 +1505,7 @@ static void resize_hpt_prepare_work(struct work_struct *work)
if (kvm->arch.resize_hpt != resize)
resize_hpt_release(kvm, resize);

mutex_unlock(&kvm->lock);
mutex_unlock(&kvm->arch.mmu_setup_lock);
}

long kvm_vm_ioctl_resize_hpt_prepare(struct kvm *kvm,
Expand All @@ -1522,7 +1522,7 @@ long kvm_vm_ioctl_resize_hpt_prepare(struct kvm *kvm,
if (shift && ((shift < 18) || (shift > 46)))
return -EINVAL;

mutex_lock(&kvm->lock);
mutex_lock(&kvm->arch.mmu_setup_lock);

resize = kvm->arch.resize_hpt;

Expand Down Expand Up @@ -1565,7 +1565,7 @@ long kvm_vm_ioctl_resize_hpt_prepare(struct kvm *kvm,
ret = 100; /* estimated time in ms */

out:
mutex_unlock(&kvm->lock);
mutex_unlock(&kvm->arch.mmu_setup_lock);
return ret;
}

Expand All @@ -1588,7 +1588,7 @@ long kvm_vm_ioctl_resize_hpt_commit(struct kvm *kvm,
if (shift && ((shift < 18) || (shift > 46)))
return -EINVAL;

mutex_lock(&kvm->lock);
mutex_lock(&kvm->arch.mmu_setup_lock);

resize = kvm->arch.resize_hpt;

Expand Down Expand Up @@ -1625,7 +1625,7 @@ long kvm_vm_ioctl_resize_hpt_commit(struct kvm *kvm,
smp_mb();
out_no_hpt:
resize_hpt_release(kvm, resize);
mutex_unlock(&kvm->lock);
mutex_unlock(&kvm->arch.mmu_setup_lock);
return ret;
}

Expand Down Expand Up @@ -1868,15 +1868,15 @@ static ssize_t kvm_htab_write(struct file *file, const char __user *buf,
return -EINVAL;

/* lock out vcpus from running while we're doing this */
mutex_lock(&kvm->lock);
mutex_lock(&kvm->arch.mmu_setup_lock);
mmu_ready = kvm->arch.mmu_ready;
if (mmu_ready) {
kvm->arch.mmu_ready = 0; /* temporarily */
/* order mmu_ready vs. vcpus_running */
smp_mb();
if (atomic_read(&kvm->arch.vcpus_running)) {
kvm->arch.mmu_ready = 1;
mutex_unlock(&kvm->lock);
mutex_unlock(&kvm->arch.mmu_setup_lock);
return -EBUSY;
}
}
Expand Down Expand Up @@ -1963,7 +1963,7 @@ static ssize_t kvm_htab_write(struct file *file, const char __user *buf,
/* Order HPTE updates vs. mmu_ready */
smp_wmb();
kvm->arch.mmu_ready = mmu_ready;
mutex_unlock(&kvm->lock);
mutex_unlock(&kvm->arch.mmu_setup_lock);

if (err)
return err;
Expand Down
31 changes: 23 additions & 8 deletions arch/powerpc/kvm/book3s_hv.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -2338,11 +2338,17 @@ static struct kvm_vcpu *kvmppc_core_vcpu_create_hv(struct kvm *kvm,
pr_devel("KVM: collision on id %u", id);
vcore = NULL;
} else if (!vcore) {
/*
* Take mmu_setup_lock for mutual exclusion
* with kvmppc_update_lpcr().
*/
err = -ENOMEM;
vcore = kvmppc_vcore_create(kvm,
id & ~(kvm->arch.smt_mode - 1));
mutex_lock(&kvm->arch.mmu_setup_lock);
kvm->arch.vcores[core] = vcore;
kvm->arch.online_vcores++;
mutex_unlock(&kvm->arch.mmu_setup_lock);
}
}
mutex_unlock(&kvm->lock);
Expand Down Expand Up @@ -3859,7 +3865,7 @@ static int kvmhv_setup_mmu(struct kvm_vcpu *vcpu)
int r = 0;
struct kvm *kvm = vcpu->kvm;

mutex_lock(&kvm->lock);
mutex_lock(&kvm->arch.mmu_setup_lock);
if (!kvm->arch.mmu_ready) {
if (!kvm_is_radix(kvm))
r = kvmppc_hv_setup_htab_rma(vcpu);
Expand All @@ -3869,7 +3875,7 @@ static int kvmhv_setup_mmu(struct kvm_vcpu *vcpu)
kvm->arch.mmu_ready = 1;
}
}
mutex_unlock(&kvm->lock);
mutex_unlock(&kvm->arch.mmu_setup_lock);
return r;
}

Expand Down Expand Up @@ -4478,7 +4484,8 @@ static void kvmppc_core_commit_memory_region_hv(struct kvm *kvm,

/*
* Update LPCR values in kvm->arch and in vcores.
* Caller must hold kvm->lock.
* Caller must hold kvm->arch.mmu_setup_lock (for mutual exclusion
* of kvm->arch.lpcr update).
*/
void kvmppc_update_lpcr(struct kvm *kvm, unsigned long lpcr, unsigned long mask)
{
Expand Down Expand Up @@ -4530,7 +4537,7 @@ void kvmppc_setup_partition_table(struct kvm *kvm)

/*
* Set up HPT (hashed page table) and RMA (real-mode area).
* Must be called with kvm->lock held.
* Must be called with kvm->arch.mmu_setup_lock held.
*/
static int kvmppc_hv_setup_htab_rma(struct kvm_vcpu *vcpu)
{
Expand Down Expand Up @@ -4618,7 +4625,10 @@ static int kvmppc_hv_setup_htab_rma(struct kvm_vcpu *vcpu)
goto out_srcu;
}

/* Must be called with kvm->lock held and mmu_ready = 0 and no vcpus running */
/*
* Must be called with kvm->arch.mmu_setup_lock held and
* mmu_ready = 0 and no vcpus running.
*/
int kvmppc_switch_mmu_to_hpt(struct kvm *kvm)
{
if (nesting_enabled(kvm))
Expand All @@ -4635,7 +4645,10 @@ int kvmppc_switch_mmu_to_hpt(struct kvm *kvm)
return 0;
}

/* Must be called with kvm->lock held and mmu_ready = 0 and no vcpus running */
/*
* Must be called with kvm->arch.mmu_setup_lock held and
* mmu_ready = 0 and no vcpus running.
*/
int kvmppc_switch_mmu_to_radix(struct kvm *kvm)
{
int err;
Expand Down Expand Up @@ -4740,6 +4753,8 @@ static int kvmppc_core_init_vm_hv(struct kvm *kvm)
char buf[32];
int ret;

mutex_init(&kvm->arch.mmu_setup_lock);

/* Allocate the guest's logical partition ID */

lpid = kvmppc_alloc_lpid();
Expand Down Expand Up @@ -5265,7 +5280,7 @@ static int kvmhv_configure_mmu(struct kvm *kvm, struct kvm_ppc_mmuv3_cfg *cfg)
if (kvmhv_on_pseries() && !radix)
return -EINVAL;

mutex_lock(&kvm->lock);
mutex_lock(&kvm->arch.mmu_setup_lock);
if (radix != kvm_is_radix(kvm)) {
if (kvm->arch.mmu_ready) {
kvm->arch.mmu_ready = 0;
Expand Down Expand Up @@ -5293,7 +5308,7 @@ static int kvmhv_configure_mmu(struct kvm *kvm, struct kvm_ppc_mmuv3_cfg *cfg)
err = 0;

out_unlock:
mutex_unlock(&kvm->lock);
mutex_unlock(&kvm->arch.mmu_setup_lock);
return err;
}

Expand Down

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