[PATCH v4 7/7] KVM: x86/mmu: Lazily allocate memslot rmaps
From: Ben Gardon
Date: Tue May 11 2021 - 13:16:58 EST
If the TDP MMU is in use, wait to allocate the rmaps until the shadow
MMU is actually used. (i.e. a nested VM is launched.) This saves memory
equal to 0.2% of guest memory in cases where the TDP MMU is used and
there are no nested guests involved.
Signed-off-by: Ben Gardon <bgardon@xxxxxxxxxx>
---
arch/x86/include/asm/kvm_host.h | 2 ++
arch/x86/kvm/mmu/mmu.c | 53 +++++++++++++++++++++++----------
arch/x86/kvm/mmu/tdp_mmu.c | 6 ++--
arch/x86/kvm/mmu/tdp_mmu.h | 4 +--
arch/x86/kvm/x86.c | 45 +++++++++++++++++++++++++++-
5 files changed, 89 insertions(+), 21 deletions(-)
diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index fc75ed49bfee..7b65f82ade1c 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -1868,4 +1868,6 @@ static inline int kvm_cpu_get_apicid(int mps_cpu)
int kvm_cpu_dirty_log_size(void);
+int alloc_all_memslots_rmaps(struct kvm *kvm);
+
#endif /* _ASM_X86_KVM_HOST_H */
diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
index b0bdb924d519..183afccd2944 100644
--- a/arch/x86/kvm/mmu/mmu.c
+++ b/arch/x86/kvm/mmu/mmu.c
@@ -1190,7 +1190,8 @@ static void kvm_mmu_write_protect_pt_masked(struct kvm *kvm,
kvm_tdp_mmu_clear_dirty_pt_masked(kvm, slot,
slot->base_gfn + gfn_offset, mask, true);
- if (!kvm->arch.memslots_have_rmaps)
+ /* Read memslots_have_rmaps before the rmaps themselves */
+ if (!smp_load_acquire(&kvm->arch.memslots_have_rmaps))
return;
while (mask) {
@@ -1223,7 +1224,8 @@ static void kvm_mmu_clear_dirty_pt_masked(struct kvm *kvm,
kvm_tdp_mmu_clear_dirty_pt_masked(kvm, slot,
slot->base_gfn + gfn_offset, mask, false);
- if (!kvm->arch.memslots_have_rmaps)
+ /* Read memslots_have_rmaps before the rmaps themselves */
+ if (!smp_load_acquire(&kvm->arch.memslots_have_rmaps))
return;
while (mask) {
@@ -1268,7 +1270,8 @@ bool kvm_mmu_slot_gfn_write_protect(struct kvm *kvm,
int i;
bool write_protected = false;
- if (kvm->arch.memslots_have_rmaps) {
+ /* Read memslots_have_rmaps before the rmaps themselves */
+ if (smp_load_acquire(&kvm->arch.memslots_have_rmaps)) {
for (i = PG_LEVEL_4K; i <= KVM_MAX_HUGEPAGE_LEVEL; ++i) {
rmap_head = __gfn_to_rmap(gfn, i, slot);
write_protected |= __rmap_write_protect(kvm, rmap_head,
@@ -1446,7 +1449,8 @@ bool kvm_unmap_gfn_range(struct kvm *kvm, struct kvm_gfn_range *range)
{
bool flush = false;
- if (kvm->arch.memslots_have_rmaps)
+ /* Read memslots_have_rmaps before the rmaps themselves */
+ if (smp_load_acquire(&kvm->arch.memslots_have_rmaps))
flush = kvm_handle_gfn_range(kvm, range, kvm_unmap_rmapp);
if (is_tdp_mmu_enabled(kvm))
@@ -1459,7 +1463,8 @@ bool kvm_set_spte_gfn(struct kvm *kvm, struct kvm_gfn_range *range)
{
bool flush = false;
- if (kvm->arch.memslots_have_rmaps)
+ /* Read memslots_have_rmaps before the rmaps themselves */
+ if (smp_load_acquire(&kvm->arch.memslots_have_rmaps))
flush = kvm_handle_gfn_range(kvm, range, kvm_set_pte_rmapp);
if (is_tdp_mmu_enabled(kvm))
@@ -1515,7 +1520,8 @@ bool kvm_age_gfn(struct kvm *kvm, struct kvm_gfn_range *range)
{
bool young = false;
- if (kvm->arch.memslots_have_rmaps)
+ /* Read memslots_have_rmaps before the rmaps themselves */
+ if (smp_load_acquire(&kvm->arch.memslots_have_rmaps))
young = kvm_handle_gfn_range(kvm, range, kvm_age_rmapp);
if (is_tdp_mmu_enabled(kvm))
@@ -1528,7 +1534,8 @@ bool kvm_test_age_gfn(struct kvm *kvm, struct kvm_gfn_range *range)
{
bool young = false;
- if (kvm->arch.memslots_have_rmaps)
+ /* Read memslots_have_rmaps before the rmaps themselves */
+ if (smp_load_acquire(&kvm->arch.memslots_have_rmaps))
young = kvm_handle_gfn_range(kvm, range, kvm_test_age_rmapp);
if (is_tdp_mmu_enabled(kvm))
@@ -3295,6 +3302,10 @@ static int mmu_alloc_shadow_roots(struct kvm_vcpu *vcpu)
}
}
+ r = alloc_all_memslots_rmaps(vcpu->kvm);
+ if (r)
+ return r;
+
write_lock(&vcpu->kvm->mmu_lock);
r = make_mmu_pages_available(vcpu);
if (r < 0)
@@ -5455,7 +5466,8 @@ static void kvm_mmu_zap_all_fast(struct kvm *kvm)
*/
kvm_reload_remote_mmus(kvm);
- if (kvm->arch.memslots_have_rmaps)
+ /* Read memslots_have_rmaps before the rmaps themselves */
+ if (smp_load_acquire(&kvm->arch.memslots_have_rmaps))
kvm_zap_obsolete_pages(kvm);
write_unlock(&kvm->mmu_lock);
@@ -5483,9 +5495,13 @@ void kvm_mmu_init_vm(struct kvm *kvm)
{
struct kvm_page_track_notifier_node *node = &kvm->arch.mmu_sp_tracker;
- kvm_mmu_init_tdp_mmu(kvm);
-
- kvm->arch.memslots_have_rmaps = true;
+ if (!kvm_mmu_init_tdp_mmu(kvm))
+ /*
+ * No smp_load/store wrappers needed here as we are in
+ * VM init and there cannot be any memslots / other threads
+ * accessing this struct kvm yet.
+ */
+ kvm->arch.memslots_have_rmaps = true;
node->track_write = kvm_mmu_pte_write;
node->track_flush_slot = kvm_mmu_invalidate_zap_pages_in_memslot;
@@ -5508,7 +5524,8 @@ void kvm_zap_gfn_range(struct kvm *kvm, gfn_t gfn_start, gfn_t gfn_end)
int i;
bool flush = false;
- if (kvm->arch.memslots_have_rmaps) {
+ /* Read memslots_have_rmaps before the rmaps themselves */
+ if (smp_load_acquire(&kvm->arch.memslots_have_rmaps)) {
write_lock(&kvm->mmu_lock);
for (i = 0; i < KVM_ADDRESS_SPACE_NUM; i++) {
slots = __kvm_memslots(kvm, i);
@@ -5559,7 +5576,8 @@ void kvm_mmu_slot_remove_write_access(struct kvm *kvm,
{
bool flush = false;
- if (kvm->arch.memslots_have_rmaps) {
+ /* Read memslots_have_rmaps before the rmaps themselves */
+ if (smp_load_acquire(&kvm->arch.memslots_have_rmaps)) {
write_lock(&kvm->mmu_lock);
flush = slot_handle_level(kvm, memslot, slot_rmap_write_protect,
start_level, KVM_MAX_HUGEPAGE_LEVEL,
@@ -5635,7 +5653,8 @@ void kvm_mmu_zap_collapsible_sptes(struct kvm *kvm,
struct kvm_memory_slot *slot = (struct kvm_memory_slot *)memslot;
bool flush;
- if (kvm->arch.memslots_have_rmaps) {
+ /* Read memslots_have_rmaps before the rmaps themselves */
+ if (smp_load_acquire(&kvm->arch.memslots_have_rmaps)) {
write_lock(&kvm->mmu_lock);
flush = slot_handle_leaf(kvm, slot, kvm_mmu_zap_collapsible_spte, true);
if (flush)
@@ -5672,7 +5691,8 @@ void kvm_mmu_slot_leaf_clear_dirty(struct kvm *kvm,
{
bool flush = false;
- if (kvm->arch.memslots_have_rmaps) {
+ /* Read memslots_have_rmaps before the rmaps themselves */
+ if (smp_load_acquire(&kvm->arch.memslots_have_rmaps)) {
write_lock(&kvm->mmu_lock);
flush = slot_handle_leaf(kvm, memslot, __rmap_clear_dirty,
false);
@@ -5705,7 +5725,8 @@ void kvm_mmu_zap_all(struct kvm *kvm)
if (is_tdp_mmu_enabled(kvm))
kvm_tdp_mmu_zap_all(kvm);
- if (!kvm->arch.memslots_have_rmaps) {
+ /* Read memslots_have_rmaps before the rmaps themselves */
+ if (!smp_load_acquire(&kvm->arch.memslots_have_rmaps)) {
write_unlock(&kvm->mmu_lock);
return;
}
diff --git a/arch/x86/kvm/mmu/tdp_mmu.c b/arch/x86/kvm/mmu/tdp_mmu.c
index 95eeb5ac6a8a..ea00c9502ba1 100644
--- a/arch/x86/kvm/mmu/tdp_mmu.c
+++ b/arch/x86/kvm/mmu/tdp_mmu.c
@@ -14,10 +14,10 @@ static bool __read_mostly tdp_mmu_enabled = false;
module_param_named(tdp_mmu, tdp_mmu_enabled, bool, 0644);
/* Initializes the TDP MMU for the VM, if enabled. */
-void kvm_mmu_init_tdp_mmu(struct kvm *kvm)
+bool kvm_mmu_init_tdp_mmu(struct kvm *kvm)
{
if (!tdp_enabled || !READ_ONCE(tdp_mmu_enabled))
- return;
+ return false;
/* This should not be changed for the lifetime of the VM. */
kvm->arch.tdp_mmu_enabled = true;
@@ -25,6 +25,8 @@ void kvm_mmu_init_tdp_mmu(struct kvm *kvm)
INIT_LIST_HEAD(&kvm->arch.tdp_mmu_roots);
spin_lock_init(&kvm->arch.tdp_mmu_pages_lock);
INIT_LIST_HEAD(&kvm->arch.tdp_mmu_pages);
+
+ return true;
}
static __always_inline void kvm_lockdep_assert_mmu_lock_held(struct kvm *kvm,
diff --git a/arch/x86/kvm/mmu/tdp_mmu.h b/arch/x86/kvm/mmu/tdp_mmu.h
index 5fdf63090451..b046ab5137a1 100644
--- a/arch/x86/kvm/mmu/tdp_mmu.h
+++ b/arch/x86/kvm/mmu/tdp_mmu.h
@@ -80,12 +80,12 @@ int kvm_tdp_mmu_get_walk(struct kvm_vcpu *vcpu, u64 addr, u64 *sptes,
int *root_level);
#ifdef CONFIG_X86_64
-void kvm_mmu_init_tdp_mmu(struct kvm *kvm);
+bool kvm_mmu_init_tdp_mmu(struct kvm *kvm);
void kvm_mmu_uninit_tdp_mmu(struct kvm *kvm);
static inline bool is_tdp_mmu_enabled(struct kvm *kvm) { return kvm->arch.tdp_mmu_enabled; }
static inline bool is_tdp_mmu_page(struct kvm_mmu_page *sp) { return sp->tdp_mmu_page; }
#else
-static inline void kvm_mmu_init_tdp_mmu(struct kvm *kvm) {}
+static inline bool kvm_mmu_init_tdp_mmu(struct kvm *kvm) { return false; }
static inline void kvm_mmu_uninit_tdp_mmu(struct kvm *kvm) {}
static inline bool is_tdp_mmu_enabled(struct kvm *kvm) { return false; }
static inline bool is_tdp_mmu_page(struct kvm_mmu_page *sp) { return false; }
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 03b6bcff2a53..fdc1b2759771 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -10920,6 +10920,8 @@ static int memslot_rmap_alloc(struct kvm_memory_slot *slot,
int lpages;
int level = i + 1;
+ WARN_ON(slot->arch.rmap[i]);
+
lpages = gfn_to_index(slot->base_gfn + npages - 1,
slot->base_gfn, level) + 1;
@@ -10935,6 +10937,46 @@ static int memslot_rmap_alloc(struct kvm_memory_slot *slot,
return 0;
}
+int alloc_all_memslots_rmaps(struct kvm *kvm)
+{
+ struct kvm_memslots *slots;
+ struct kvm_memory_slot *slot;
+ int r = 0;
+ int i;
+
+ /*
+ * Check memslots_have_rmaps early before acquiring the
+ * slots_arch_lock below.
+ */
+ if (smp_load_acquire(&kvm->arch.memslots_have_rmaps))
+ return 0;
+
+ mutex_lock(&kvm->slots_arch_lock);
+
+ /*
+ * Read memslots_have_rmaps again, under the slots arch lock,
+ * before allocating the rmaps
+ */
+ if (smp_load_acquire(&kvm->arch.memslots_have_rmaps))
+ return 0;
+
+ for (i = 0; i < KVM_ADDRESS_SPACE_NUM; i++) {
+ slots = __kvm_memslots(kvm, i);
+ kvm_for_each_memslot(slot, slots) {
+ r = memslot_rmap_alloc(slot, slot->npages);
+ if (r) {
+ mutex_unlock(&kvm->slots_arch_lock);
+ return r;
+ }
+ }
+ }
+
+ /* Write rmap pointers before memslots_have_rmaps */
+ smp_store_release(&kvm->arch.memslots_have_rmaps, true);
+ mutex_unlock(&kvm->slots_arch_lock);
+ return 0;
+}
+
static int kvm_alloc_memslot_metadata(struct kvm *kvm,
struct kvm_memory_slot *slot,
unsigned long npages)
@@ -10949,7 +10991,8 @@ static int kvm_alloc_memslot_metadata(struct kvm *kvm,
*/
memset(&slot->arch, 0, sizeof(slot->arch));
- if (kvm->arch.memslots_have_rmaps) {
+ /* Read memslots_have_rmaps before allocating the rmaps */
+ if (smp_load_acquire(&kvm->arch.memslots_have_rmaps)) {
r = memslot_rmap_alloc(slot, npages);
if (r)
return r;
--
2.31.1.607.g51e8a6a459-goog