[RFC PATCH v3 11/19] KVM: x86: nSVM: implement shadowing of AVIC's physical id table

Maxim Levitsky
2022-04-27T20:06:07Z

Implement the shadow physical id table and its
write tracking code which will be soon used for the nested AVIC.

Signed-off-by: Maxim Levitsky <mlevitsk@redhat.com>
---
arch/x86/kvm/svm/avic.c | 461 +++++++++++++++++++++++++++++++++++++++-
arch/x86/kvm/svm/svm.h | 71 +++++++
2 files changed, 524 insertions(+), 8 deletions(-)

diff --git a/arch/x86/kvm/svm/avic.c b/arch/x86/kvm/svm/avic.c
index e5cbbb97fbab6..f462b7e48e3ca 100644
--- a/arch/x86/kvm/svm/avic.c
+++ b/arch/x86/kvm/svm/avic.c
@@ -51,6 +51,433 @@ static u32 next_vm_id = 0;
static bool next_vm_id_wrapped = 0;
static DEFINE_SPINLOCK(svm_vm_data_hash_lock);

+
+static inline struct kvm_vcpu *avic_vcpu_by_l1_apicid(struct kvm *kvm,
+ int l1_apicid)
+{
+ WARN_ON(l1_apicid == -1);
+ return kvm_get_vcpu_by_id(kvm, l1_apicid);
+}
+
+static void avic_physid_shadow_entry_set_vcpu(struct kvm *kvm,
+ struct avic_physid_table *t,
+ int n,
+ int new_l1_apicid)
+{
+ struct avic_physid_entry_descr *e = &t->entries[n];
+ u64 sentry = READ_ONCE(*e->sentry);
+ u64 old_sentry = sentry;
+ struct kvm_vcpu *new_vcpu = NULL;
+ int l0_apicid = -1;
+
+ WARN_ON(!test_bit(n, t->valid_entires));
+
+ if (!list_empty(&e->link))
+ list_del_init(&e->link);
+
+ if (new_l1_apicid != -1)
+ new_vcpu = avic_vcpu_by_l1_apicid(kvm, new_l1_apicid);
+
+ if (new_vcpu)
+ l0_apicid = kvm_cpu_get_apicid(new_vcpu->cpu);
+
+ physid_entry_set_apicid(&sentry, l0_apicid);
+
+ trace_kvm_avic_physid_update_vcpu_guest(new_l1_apicid, l0_apicid);
+
+ if (sentry != old_sentry)
+ WRITE_ONCE(*e->sentry, sentry);
+}
+
+static void avic_physid_shadow_entry_create(struct kvm *kvm,
+ struct avic_physid_table *t,
+ int n,
+ u64 gentry)
+{
+ struct avic_physid_entry_descr *e = &t->entries[n];
+ struct page *backing_page;
+ u64 backing_page_gpa = physid_entry_get_backing_table(gentry);
+ int l1_apic_id = physid_entry_get_apicid(gentry);
+ hpa_t backing_page_hpa;
+ u64 sentry = 0;
+
+
+ if (backing_page_gpa == INVALID_BACKING_PAGE)
+ return;
+
+ /* Pin the APIC backing page */
+ backing_page = gfn_to_page(kvm, gpa_to_gfn(backing_page_gpa));
+
+ if (is_error_page(backing_page))
+ /* Invalid GPA in the guest entry - point to a dummy entry */
+ backing_page_hpa = t->dummy_page_hpa;
+ else
+ backing_page_hpa = page_to_phys(backing_page);
+
+ physid_entry_set_backing_table(&sentry, backing_page_hpa);
+
+ e->gentry = gentry;
+ *e->sentry = sentry;
+
+ if (test_and_set_bit(n, t->valid_entires))
+ WARN_ON(1);
+
+ if (backing_page_hpa != t->dummy_page_hpa)
+ avic_physid_shadow_entry_set_vcpu(kvm, t, n, l1_apic_id);
+}
+
+static void avic_physid_shadow_entry_remove(struct kvm *kvm,
+ struct avic_physid_table *t,
+ int n)
+{
+ struct avic_physid_entry_descr *e = &t->entries[n];
+ hpa_t backing_page_hpa;
+
+ if (!test_and_clear_bit(n, t->valid_entires))
+ WARN_ON(1);
+
+ /* Release the APIC backing page */
+ backing_page_hpa = physid_entry_get_backing_table(*e->sentry);
+
+ if (backing_page_hpa != t->dummy_page_hpa)
+ kvm_release_pfn_dirty(backing_page_hpa >> PAGE_SHIFT);
+
+ if (!list_empty(&e->link))
+ list_del_init(&e->link);
+
+ e->gentry = 0;
+ *e->sentry = 0;
+}
+
+
+static bool
+avic_physid_shadow_table_setup_write_tracking(struct kvm *kvm,
+ struct avic_physid_table *t,
+ bool enable)
+{
+ struct kvm_memory_slot *slot;
+
+ write_lock(&kvm->mmu_lock);
+ slot = gfn_to_memslot(kvm, t->gfn);
+ if (!slot) {
+ write_unlock(&kvm->mmu_lock);
+ return false;
+ }
+
+ if (enable)
+ kvm_slot_page_track_add_page(kvm, slot, t->gfn, KVM_PAGE_TRACK_WRITE);
+ else
+ kvm_slot_page_track_remove_page(kvm, slot, t->gfn, KVM_PAGE_TRACK_WRITE);
+ write_unlock(&kvm->mmu_lock);
+ return true;
+}
+
+static void
+avic_physid_shadow_table_erase(struct kvm *kvm, struct avic_physid_table *t)
+{
+ int i;
+
+ if (!t->nentries)
+ return;
+
+ avic_physid_shadow_table_setup_write_tracking(kvm, t, false);
+
+ for_each_set_bit(i, t->valid_entires, AVIC_MAX_PHYSICAL_ID_COUNT)
+ avic_physid_shadow_entry_remove(kvm, t, i);
+
+ t->nentries = 0;
+ t->flood_count = 0;
+}
+
+static struct avic_physid_table *
+avic_physid_shadow_table_alloc(struct kvm *kvm, gfn_t gfn)
+{
+ struct avic_physid_entry_descr *e;
+ struct avic_physid_table *t;
+ struct kvm_svm *kvm_svm = to_kvm_svm(kvm);
+ u64 *shadow_table_address;
+ int i;
+
+ if (kvm_page_track_write_tracking_enable(kvm))
+ return NULL;
+
+ lockdep_assert_held(&kvm_svm->avic.tables_lock);
+
+ t = kzalloc(sizeof(*t), GFP_KERNEL_ACCOUNT);
+ if (!t)
+ return NULL;
+
+ t->shadow_table = alloc_page(GFP_KERNEL_ACCOUNT|__GFP_ZERO);
+ if (!t->shadow_table)
+ goto err_free_table;
+
+ shadow_table_address = page_address(t->shadow_table);
+ t->shadow_table_hpa = __sme_set(page_to_phys(t->shadow_table));
+
+ for (i = 0; i < ARRAY_SIZE(t->entries); i++) {
+ e = &t->entries[i];
+ e->sentry = &shadow_table_address[i];
+ e->gentry = 0;
+ INIT_LIST_HEAD(&e->link);
+ }
+
+ t->gfn = gfn;
+ t->refcount = 1;
+
+ list_add_tail(&t->link, &kvm_svm->avic.physid_tables);
+
+ t->dummy_page_hpa = page_to_phys(kvm_svm->avic.invalid_physid_page);
+
+ trace_kvm_avic_physid_table_alloc(gfn_to_gpa(gfn));
+ return t;
+
+err_free_table:
+ kfree(t);
+ return NULL;
+}
+
+static void
+avic_physid_shadow_table_free(struct kvm *kvm, struct avic_physid_table *t)
+{
+ struct kvm_svm *kvm_svm = to_kvm_svm(kvm);
+
+ lockdep_assert_held(&kvm_svm->avic.tables_lock);
+
+ WARN_ON(t->refcount);
+
+ avic_physid_shadow_table_erase(kvm, t);
+
+ trace_kvm_avic_physid_table_free(gfn_to_gpa(t->gfn));
+
+ hlist_del(&t->hash_link);
+ list_del(&t->link);
+ __free_page(t->shadow_table);
+ kfree(t);
+}
+
+static struct avic_physid_table *
+__avic_physid_shadow_table_get(struct hlist_head *head, gfn_t gfn)
+{
+ struct avic_physid_table *t;
+
+ hlist_for_each_entry(t, head, hash_link)
+ if (t->gfn == gfn) {
+ t->refcount++;
+ return t;
+ }
+ return NULL;
+}
+
+struct avic_physid_table *
+avic_physid_shadow_table_get(struct kvm_vcpu *vcpu, gfn_t gfn)
+{
+ struct kvm_svm *kvm_svm = to_kvm_svm(vcpu->kvm);
+ struct hlist_head *hlist;
+ struct avic_physid_table *t;
+
+ mutex_lock(&kvm_svm->avic.tables_lock);
+
+ hlist = &kvm_svm->avic.physid_gpa_hash[avic_physid_hash(gfn)];
+ t = __avic_physid_shadow_table_get(hlist, gfn);
+ if (!t) {
+ t = avic_physid_shadow_table_alloc(vcpu->kvm, gfn);
+ if (!t)
+ goto out_unlock;
+ hlist_add_head(&t->hash_link, hlist);
+ }
+out_unlock:
+ mutex_unlock(&kvm_svm->avic.tables_lock);
+ return t;
+}
+
+static void
+__avic_physid_shadow_table_put(struct kvm *kvm, struct avic_physid_table *t)
+{
+ WARN_ON(t->refcount <= 0);
+ if (--t->refcount == 0)
+ avic_physid_shadow_table_free(kvm, t);
+}
+
+void avic_physid_shadow_table_put(struct kvm *kvm, struct avic_physid_table *t)
+{
+ struct kvm_svm *kvm_svm = to_kvm_svm(kvm);
+
+ mutex_lock(&kvm_svm->avic.tables_lock);
+ __avic_physid_shadow_table_put(kvm, t);
+ mutex_unlock(&kvm_svm->avic.tables_lock);
+}
+
+static void avic_physid_shadow_table_invalidate(struct kvm *kvm,
+ struct avic_physid_table *t)
+{
+ struct kvm_svm *kvm_svm = to_kvm_svm(kvm);
+
+ lockdep_assert_held(&kvm_svm->avic.tables_lock);
+ avic_physid_shadow_table_erase(kvm, t);
+}
+
+int avic_physid_shadow_table_sync(struct kvm_vcpu *vcpu,
+ struct avic_physid_table *t, int nentries)
+{
+ struct kvm_svm *kvm_svm = to_kvm_svm(vcpu->kvm);
+ struct kvm_host_map map;
+ u64 *gentries;
+ int i;
+ int ret = 0;
+
+ mutex_lock(&kvm_svm->avic.tables_lock);
+
+ if (t->nentries >= nentries)
+ goto out_unlock;
+
+
+ trace_kvm_avic_physid_table_reload(gfn_to_gpa(t->gfn), t->nentries, nentries);
+
+ if (t->nentries == 0) {
+ if (!avic_physid_shadow_table_setup_write_tracking(vcpu->kvm, t, true)) {
+ ret = -EFAULT;
+ goto out_unlock;
+ }
+ }
+
+ if (kvm_vcpu_map(vcpu, t->gfn, &map)) {
+ ret = -EFAULT;
+ goto out_unlock;
+ }
+
+ gentries = (u64 *)map.hva;
+
+ for (i = t->nentries ; i < nentries ; i++)
+ avic_physid_shadow_entry_create(vcpu->kvm, t, i, gentries[i]);
+
+ /* publish the table before setting nentries */
+ wmb();
+ WRITE_ONCE(t->nentries, nentries);
+
+ kvm_vcpu_unmap(vcpu, &map, false);
+out_unlock:
+ mutex_unlock(&kvm_svm->avic.tables_lock);
+ return ret;
+}
+
+static void avic_physid_shadow_table_track_write(struct kvm_vcpu *vcpu,
+ gpa_t gpa,
+ const u8 *new,
+ int bytes,
+ struct kvm_page_track_notifier_node *node)
+{
+ struct kvm_svm *kvm_svm = to_kvm_svm(vcpu->kvm);
+ struct hlist_head *hlist;
+ struct avic_physid_table *t;
+ gfn_t gfn = gpa_to_gfn(gpa);
+ unsigned int page_offset = offset_in_page(gpa);
+ unsigned int entry_offset = page_offset & 0x7;
+ int first = page_offset / sizeof(u64);
+ int last = (page_offset + bytes - 1) / sizeof(u64);
+ u64 new_entry, old_entry;
+ int l1_apic_id;
+
+ if (WARN_ON_ONCE(bytes == 0))
+ return;
+
+ mutex_lock(&kvm_svm->avic.tables_lock);
+
+ hlist = &kvm_svm->avic.physid_gpa_hash[avic_physid_hash(gfn)];
+ t = __avic_physid_shadow_table_get(hlist, gfn);
+
+ if (!t)
+ goto out_unlock;
+
+ trace_kvm_avic_physid_table_write(gpa, bytes);
+
+ /*
+ * Update policy:
+ *
+ * Only a write to a single entry, entry that had a valid backing page
+ * on the last VM entry with this page, and only if the
+ * write touches only the is_running and/or apic_id part of this entry
+ * is allowed.
+ *
+ * Writes outside of known number of entries are ignored to support
+ * case when the guest is adding entries to end of the page
+ * in the process of a cpu hotplug.
+ *
+ * All other writes, which are not supposed to happen during
+ * use of the page, cause the page to be invalidated,
+ * and read as a whole, next time it is used by a vCPU for VM entry.
+ */
+
+ if (first >= t->nentries)
+ goto out_table_put;
+
+ if (first != last || !test_bit(first, t->valid_entires))
+ goto invalidate;
+
+ /* update the entry with written bytes */
+ old_entry = t->entries[first].gentry;
+ new_entry = old_entry;
+ memcpy(((u8 *)&new_entry) + entry_offset, new, bytes);
+
+ /* if backing page changed, invalidate the whole page*/
+ if (physid_entry_get_backing_table(old_entry) !=
+ physid_entry_get_backing_table(new_entry))
+ goto invalidate;
+
+ /*
+ * Detect write flooding to physid pages that might not be used
+ * for the purpose anymore
+ */
+ if (!atomic_read(&t->usecount)) {
+ if (++t->flood_count > t->nentries * AVIC_PHYSID_FLOOD_COUNT)
+ goto invalidate;
+ } else {
+ t->flood_count = 0;
+ }
+
+ /* Update the backing cpu */
+ l1_apic_id = physid_entry_get_apicid(new_entry);
+ avic_physid_shadow_entry_set_vcpu(vcpu->kvm, t, first, l1_apic_id);
+ t->entries[first].gentry = new_entry;
+ goto out_table_put;
+invalidate:
+ avic_physid_shadow_table_invalidate(vcpu->kvm, t);
+out_table_put:
+ __avic_physid_shadow_table_put(vcpu->kvm, t);
+out_unlock:
+ mutex_unlock(&kvm_svm->avic.tables_lock);
+}
+
+static void avic_physid_shadow_table_flush_memslot(struct kvm *kvm,
+ struct kvm_memory_slot *slot,
+ struct kvm_page_track_notifier_node *node)
+{
+ struct kvm_svm *kvm_svm = to_kvm_svm(kvm);
+ struct avic_physid_table *t, *n;
+ int i;
+
+ mutex_lock(&kvm_svm->avic.tables_lock);
+
+ list_for_each_entry_safe(t, n, &kvm_svm->avic.physid_tables, link) {
+
+ if (gfn_in_memslot(slot, t->gfn)) {
+ avic_physid_shadow_table_invalidate(kvm, t);
+ continue;
+ }
+
+ for_each_set_bit(i, t->valid_entires, AVIC_MAX_PHYSICAL_ID_COUNT) {
+ u64 gentry = t->entries[i].gentry;
+ gpa_t gpa = physid_entry_get_backing_table(gentry);
+
+ if (gfn_in_memslot(slot, gpa_to_gfn(gpa))) {
+ avic_physid_shadow_table_invalidate(kvm, t);
+ break;
+ }
+ }
+ }
+ mutex_unlock(&kvm_svm->avic.tables_lock);
+}
+
+
/*
* This is a wrapper of struct amd_iommu_ir_data.
*/
@@ -113,18 +540,22 @@ void avic_vm_destroy(struct kvm *kvm)
__free_page(avic->logical_id_table_page);
if (avic->physical_id_table_page)
__free_page(avic->physical_id_table_page);
+ if (avic->invalid_physid_page)
+ __free_page(avic->invalid_physid_page);

spin_lock_irqsave(&svm_vm_data_hash_lock, flags);
hash_del(&avic->hnode);
spin_unlock_irqrestore(&svm_vm_data_hash_lock, flags);
+
+
+ kvm_page_track_unregister_notifier(kvm, &avic->write_tracker);
}

int avic_vm_init(struct kvm *kvm)
{
unsigned long flags;
int err = -ENOMEM;
- struct page *p_page;
- struct page *l_page;
+ struct page *page;
struct kvm_svm_avic *avic = &to_kvm_svm(kvm)->avic;
u32 vm_id;

@@ -132,18 +563,25 @@ int avic_vm_init(struct kvm *kvm)
return 0;

/* Allocating physical APIC ID table (4KB) */
- p_page = alloc_page(GFP_KERNEL_ACCOUNT | __GFP_ZERO);
- if (!p_page)
+ page = alloc_page(GFP_KERNEL_ACCOUNT | __GFP_ZERO);
+ if (!page)
goto free_avic;

- avic->physical_id_table_page = p_page;
+ avic->physical_id_table_page = page;

/* Allocating logical APIC ID table (4KB) */
- l_page = alloc_page(GFP_KERNEL_ACCOUNT | __GFP_ZERO);
- if (!l_page)
+ page = alloc_page(GFP_KERNEL_ACCOUNT | __GFP_ZERO);
+ if (!page)
goto free_avic;

- avic->logical_id_table_page = l_page;
+ avic->logical_id_table_page = page;
+
+ /* Allocating a dummy page for invalid nested avic physid entries */
+ page = alloc_page(GFP_KERNEL_ACCOUNT | __GFP_ZERO);
+ if (!page)
+ goto free_avic;
+
+ avic->invalid_physid_page = page;

spin_lock_irqsave(&svm_vm_data_hash_lock, flags);
again:
@@ -165,6 +603,13 @@ 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);

+ mutex_init(&avic->tables_lock);
+ INIT_LIST_HEAD(&avic->physid_tables);
+
+ avic->write_tracker.track_write = avic_physid_shadow_table_track_write;
+ avic->write_tracker.track_flush_slot = avic_physid_shadow_table_flush_memslot;
+
+ kvm_page_track_register_notifier(kvm, &avic->write_tracker);
return 0;

free_avic:
diff --git a/arch/x86/kvm/svm/svm.h b/arch/x86/kvm/svm/svm.h
index dfca4c06e2071..fc15e1f938793 100644
--- a/arch/x86/kvm/svm/svm.h
+++ b/arch/x86/kvm/svm/svm.h
@@ -18,6 +18,7 @@
#include <linux/kvm_types.h>
#include <linux/kvm_host.h>
#include <linux/bits.h>
+#include <linux/hash.h>

#include <asm/svm.h>
#include <asm/sev-common.h>
@@ -89,13 +90,33 @@ struct kvm_sev_info {
};

+#define AVIC_PHYSID_HASH_SHIFT 8
+#define AVIC_PHYSID_HASH_SIZE (1 << AVIC_PHYSID_HASH_SHIFT)
+
struct kvm_svm_avic {
u32 vm_id;
struct page *logical_id_table_page;
struct page *physical_id_table_page;
struct hlist_node hnode;
+
+ struct mutex tables_lock;
+
+ /* List of all shadow tables */
+ struct list_head physid_tables;
+
+ /* GPA hash table to find a shadow table via its GPA */
+ struct hlist_head physid_gpa_hash[AVIC_PHYSID_HASH_SIZE];
+
+ struct kvm_page_track_notifier_node write_tracker;
+
+ struct page *invalid_physid_page;
};

+static __always_inline unsigned int avic_physid_hash(gfn_t gfn)
+{
+ return hash_64(gfn, AVIC_PHYSID_HASH_SHIFT);
+}
+
struct kvm_svm {
struct kvm kvm;
struct kvm_svm_avic avic;
@@ -147,6 +168,49 @@ struct vmcb_ctrl_area_cached {
u8 reserved_sw[32];
};

+struct avic_physid_entry_descr {
+ struct list_head link;
+
+ /* cached value of guest entry */
+ u64 gentry;
+
+ /* shadow table entry pointer*/
+ u64 *sentry;
+};
+
+#define AVIC_PHYSID_FLOOD_COUNT 1000
+
+struct avic_physid_table {
+ /* List of all tables member */
+ struct list_head link;
+
+ /* GPA hash of all tables member */
+ struct hlist_node hash_link;
+
+ /* GPA of the table in guest memory*/
+ gfn_t gfn;
+
+ /* Number of entries that we shadow and which are valid*/
+ int nentries;
+ DECLARE_BITMAP(valid_entires, AVIC_MAX_PHYSICAL_ID_COUNT);
+
+ struct avic_physid_entry_descr entries[AVIC_MAX_PHYSICAL_ID_COUNT];
+
+ /* Guest visible shadow table */
+ struct page *shadow_table;
+ hpa_t shadow_table_hpa;
+ hpa_t dummy_page_hpa;
+
+ /* Number of vCPUs which have reference to this table */
+ int refcount;
+
+ /* number of vCPUs that are in guest mode and use this table */
+ atomic_t usecount;
+
+ /* Number of writes to this page between uses of it*/
+ int flood_count;
+};
+
struct svm_nested_state {
struct kvm_vmcb_info vmcb02;
u64 hsave_msr;
@@ -628,6 +692,13 @@ void avic_vcpu_unblocking(struct kvm_vcpu *vcpu);
void avic_ring_doorbell(struct kvm_vcpu *vcpu);
unsigned long avic_vcpu_get_apicv_inhibit_reasons(struct kvm_vcpu *vcpu);

+struct avic_physid_table *
+avic_physid_shadow_table_get(struct kvm_vcpu *vcpu, gfn_t gfn);
+void avic_physid_shadow_table_put(struct kvm *kvm, struct avic_physid_table *t);
+int avic_physid_shadow_table_sync(struct kvm_vcpu *vcpu,
+ struct avic_physid_table *t, int nentries);
+
+
#define INVALID_BACKING_PAGE (~(u64)0)

static inline u64 physid_entry_get_backing_table(u64 entry)
--
2.26.3