[RFC PATCH v3 12/19] KVM: x86: nSVM: make nested AVIC physid write tracking be aware of the host scheduling

Maxim Levitsky
2022-04-27T20:06:26Z

For each vCPU
- store a linked list of all shadow physical id entries
which address it.

- Update those entries when this vCPU is scheduled
in/out

- update this list, when physid tables are modified by
other means (guest write and/or table sync)

To avoid races vs vcpu schedule, use a spinlock.

Signed-off-by: Maxim Levitsky <mlevitsk@redhat.com>
---
arch/x86/kvm/svm/avic.c | 113 +++++++++++++++++++++++++++++++++++++---
arch/x86/kvm/svm/svm.c | 7 +++
arch/x86/kvm/svm/svm.h | 10 ++++
3 files changed, 122 insertions(+), 8 deletions(-)

diff --git a/arch/x86/kvm/svm/avic.c b/arch/x86/kvm/svm/avic.c
index f462b7e48e3ca..34da9fabd5194 100644
--- a/arch/x86/kvm/svm/avic.c
+++ b/arch/x86/kvm/svm/avic.c
@@ -67,8 +67,12 @@ static void avic_physid_shadow_entry_set_vcpu(struct kvm *kvm,
struct avic_physid_entry_descr *e = &t->entries[n];
u64 sentry = READ_ONCE(*e->sentry);
u64 old_sentry = sentry;
+ struct kvm_svm *kvm_svm = to_kvm_svm(kvm);
struct kvm_vcpu *new_vcpu = NULL;
int l0_apicid = -1;
+ unsigned long flags;
+
+ raw_spin_lock_irqsave(&kvm_svm->avic.table_entries_lock, flags);

WARN_ON(!test_bit(n, t->valid_entires));

@@ -79,6 +83,9 @@ static void avic_physid_shadow_entry_set_vcpu(struct kvm *kvm,
new_vcpu = avic_vcpu_by_l1_apicid(kvm, new_l1_apicid);

if (new_vcpu)
+ list_add_tail(&e->link, &to_svm(new_vcpu)->nested.physid_ref_entries);
+
+ if (new_vcpu && to_svm(new_vcpu)->nested_avic_active)
l0_apicid = kvm_cpu_get_apicid(new_vcpu->cpu);

physid_entry_set_apicid(&sentry, l0_apicid);
@@ -87,6 +94,8 @@ static void avic_physid_shadow_entry_set_vcpu(struct kvm *kvm,

if (sentry != old_sentry)
WRITE_ONCE(*e->sentry, sentry);
+
+ raw_spin_unlock_irqrestore(&kvm_svm->avic.table_entries_lock, flags);
}

static void avic_physid_shadow_entry_create(struct kvm *kvm,
@@ -131,7 +140,11 @@ static void avic_physid_shadow_entry_remove(struct kvm *kvm,
int n)
{
struct avic_physid_entry_descr *e = &t->entries[n];
+ struct kvm_svm *kvm_svm = to_kvm_svm(kvm);
hpa_t backing_page_hpa;
+ unsigned long flags;
+
+ raw_spin_lock_irqsave(&kvm_svm->avic.table_entries_lock, flags);

if (!test_and_clear_bit(n, t->valid_entires))
WARN_ON(1);
@@ -147,8 +160,49 @@ static void avic_physid_shadow_entry_remove(struct kvm *kvm,

e->gentry = 0;
*e->sentry = 0;
+
+ raw_spin_unlock_irqrestore(&kvm_svm->avic.table_entries_lock, flags);
}

+static void avic_update_peer_physid_entries(struct kvm_vcpu *vcpu, int cpu)
+{
+ /*
+ * Update all shadow physid tables which contain entries
+ * which reference this vCPU with its new physical location
+ */
+ struct kvm_svm *kvm_svm = to_kvm_svm(vcpu->kvm);
+ struct vcpu_svm *vcpu_svm = to_svm(vcpu);
+ struct avic_physid_entry_descr *e;
+ int updated_nentries = 0;
+ int l0_apicid = -1;
+ unsigned long flags;
+ bool new_active = cpu != -1;
+
+ if (cpu != -1)
+ l0_apicid = kvm_cpu_get_apicid(cpu);
+
+ raw_spin_lock_irqsave(&kvm_svm->avic.table_entries_lock, flags);
+
+ list_for_each_entry(e, &vcpu_svm->nested.physid_ref_entries, link) {
+ u64 sentry = READ_ONCE(*e->sentry);
+ u64 old_sentry = sentry;
+
+ physid_entry_set_apicid(&sentry, l0_apicid);
+
+ if (sentry != old_sentry) {
+ updated_nentries++;
+ WRITE_ONCE(*e->sentry, sentry);
+ }
+ }
+
+ if (updated_nentries)
+ trace_kvm_avic_physid_update_vcpu_host(vcpu->vcpu_id,
+ l0_apicid, updated_nentries);
+
+ vcpu_svm->nested_avic_active = new_active;
+
+ raw_spin_unlock_irqrestore(&kvm_svm->avic.table_entries_lock, flags);
+}

static bool
avic_physid_shadow_table_setup_write_tracking(struct kvm *kvm,
@@ -603,6 +657,7 @@ int avic_vm_init(struct kvm *kvm)
hash_add(svm_vm_data_hash, &avic->hnode, avic->vm_id);
spin_unlock_irqrestore(&svm_vm_data_hash_lock, flags);

+ raw_spin_lock_init(&avic->table_entries_lock);
mutex_init(&avic->tables_lock);
INIT_LIST_HEAD(&avic->physid_tables);

@@ -1428,9 +1483,51 @@ static void avic_vcpu_load(struct kvm_vcpu *vcpu)
static void avic_vcpu_put(struct kvm_vcpu *vcpu)
{
preempt_disable();
-
__avic_vcpu_put(vcpu);
+ preempt_enable();
+}
+

+void __nested_avic_load(struct kvm_vcpu *vcpu, int cpu)
+{
+ struct vcpu_svm *svm = to_svm(vcpu);
+
+ lockdep_assert_preemption_disabled();
+
+ /*
+ * For the same reason as in __avic_vcpu_load there is no
+ * need to load nested AVIC when this vCPU is blocking
+ */
+ if (kvm_vcpu_is_blocking(vcpu))
+ return;
+
+ if (svm->nested.initialized)
+ avic_update_peer_physid_entries(vcpu, cpu);
+}
+
+void __nested_avic_put(struct kvm_vcpu *vcpu)
+{
+ struct vcpu_svm *svm = to_svm(vcpu);
+
+ lockdep_assert_preemption_disabled();
+
+ if (svm->nested.initialized)
+ avic_update_peer_physid_entries(vcpu, -1);
+}
+
+void nested_avic_load(struct kvm_vcpu *vcpu)
+{
+ int cpu = get_cpu();
+
+ WARN_ON(cpu != vcpu->cpu);
+ __nested_avic_load(vcpu, cpu);
+ put_cpu();
+}
+
+void nested_avic_put(struct kvm_vcpu *vcpu)
+{
+ preempt_disable();
+ __nested_avic_put(vcpu);
preempt_enable();
}

@@ -1468,9 +1565,6 @@ void avic_refresh_apicv_exec_ctrl(struct kvm_vcpu *vcpu)

void avic_vcpu_blocking(struct kvm_vcpu *vcpu)
{
- if (!kvm_vcpu_apicv_active(vcpu))
- return;
-
/*
* Unload the AVIC when the vCPU is about to block, _before_
* the vCPU actually blocks.
@@ -1484,13 +1578,16 @@ void avic_vcpu_blocking(struct kvm_vcpu *vcpu)
* IRR and reading IsRunning; the lack of this barrier might be
* the cause of errata #1235).
*/
- avic_vcpu_put(vcpu);
+ if (kvm_vcpu_apicv_active(vcpu))
+ avic_vcpu_put(vcpu);
+
+ nested_avic_put(vcpu);
}

void avic_vcpu_unblocking(struct kvm_vcpu *vcpu)
{
- if (!kvm_vcpu_apicv_active(vcpu))
- return;
+ if (kvm_vcpu_apicv_active(vcpu))
+ avic_vcpu_load(vcpu);

- avic_vcpu_load(vcpu);
+ nested_avic_load(vcpu);
}
diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
index 75b4f3ac8b1a0..76fbee2c8c5d7 100644
--- a/arch/x86/kvm/svm/svm.c
+++ b/arch/x86/kvm/svm/svm.c
@@ -1302,6 +1302,8 @@ static int svm_vcpu_create(struct kvm_vcpu *vcpu)

svm->guest_state_loaded = false;

+ INIT_LIST_HEAD(&svm->nested.physid_ref_entries);
+
return 0;

error_free_vmsa_page:
@@ -1391,8 +1393,11 @@ static void svm_vcpu_load(struct kvm_vcpu *vcpu, int cpu)
sd->current_vmcb = svm->vmcb;
indirect_branch_prediction_barrier();
}
+
if (kvm_vcpu_apicv_active(vcpu))
__avic_vcpu_load(vcpu, cpu);
+
+ __nested_avic_load(vcpu, cpu);
}

static void svm_vcpu_put(struct kvm_vcpu *vcpu)
@@ -1400,6 +1405,8 @@ static void svm_vcpu_put(struct kvm_vcpu *vcpu)
if (kvm_vcpu_apicv_active(vcpu))
__avic_vcpu_put(vcpu);

+ __nested_avic_put(vcpu);
+
svm_prepare_host_switch(vcpu);

++vcpu->stat.host_state_reload;
diff --git a/arch/x86/kvm/svm/svm.h b/arch/x86/kvm/svm/svm.h
index fc15e1f938793..401449dbce65d 100644
--- a/arch/x86/kvm/svm/svm.h
+++ b/arch/x86/kvm/svm/svm.h
@@ -99,6 +99,7 @@ struct kvm_svm_avic {
struct page *physical_id_table_page;
struct hlist_node hnode;

+ raw_spinlock_t table_entries_lock;
struct mutex tables_lock;

/* List of all shadow tables */
@@ -244,6 +245,9 @@ struct svm_nested_state {
* on its side.
*/
bool force_msr_bitmap_recalc;
+
+ /* All AVIC shadow PID table entry descriptors that reference this vCPU */
+ struct list_head physid_ref_entries;
};

struct vcpu_sev_es_state {
@@ -311,6 +315,7 @@ struct vcpu_svm {
u32 dfr_reg;
struct page *avic_backing_page;
u64 *avic_physical_id_cache;
+ bool nested_avic_active;

/*
* Per-vcpu list of struct amd_svm_iommu_ir:
@@ -678,6 +683,11 @@ int avic_unaccelerated_access_interception(struct kvm_vcpu *vcpu);
int avic_init_vcpu(struct vcpu_svm *svm);
void __avic_vcpu_load(struct kvm_vcpu *vcpu, int cpu);
void __avic_vcpu_put(struct kvm_vcpu *vcpu);
+void __nested_avic_load(struct kvm_vcpu *vcpu, int cpu);
+void __nested_avic_put(struct kvm_vcpu *vcpu);
+void nested_avic_load(struct kvm_vcpu *vcpu);
+void nested_avic_put(struct kvm_vcpu *vcpu);
+
void avic_apicv_post_state_restore(struct kvm_vcpu *vcpu);
void avic_set_virtual_apic_mode(struct kvm_vcpu *vcpu);
void avic_refresh_apicv_exec_ctrl(struct kvm_vcpu *vcpu);
--
2.26.3