From d501f747ef5c0ac0c917f9a6781d04ae4ae39d63 Mon Sep 17 00:00:00 2001 From: Ben Gardon Date: Tue, 18 May 2021 10:34:14 -0700 Subject: [PATCH] KVM: x86/mmu: Lazily allocate memslot rmaps 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 Message-Id: <20210518173414.450044-8-bgardon@google.com> Signed-off-by: Paolo Bonzini --- arch/x86/include/asm/kvm_host.h | 2 ++ arch/x86/kvm/mmu.h | 7 ++++- arch/x86/kvm/mmu/mmu.c | 14 +++++++--- arch/x86/kvm/mmu/tdp_mmu.c | 6 +++-- arch/x86/kvm/mmu/tdp_mmu.h | 4 +-- arch/x86/kvm/x86.c | 46 +++++++++++++++++++++++++++++++++ 6 files changed, 71 insertions(+), 8 deletions(-) diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h index 11798a9ff3e9..dadb545c429f 100644 --- a/arch/x86/include/asm/kvm_host.h +++ b/arch/x86/include/asm/kvm_host.h @@ -1869,4 +1869,6 @@ 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.h b/arch/x86/kvm/mmu.h index af09c47b1aa2..9d8550af994c 100644 --- a/arch/x86/kvm/mmu.h +++ b/arch/x86/kvm/mmu.h @@ -234,7 +234,12 @@ void kvm_mmu_pre_destroy_vm(struct kvm *kvm); static inline bool kvm_memslots_have_rmaps(struct kvm *kvm) { - return kvm->arch.memslots_have_rmaps; + /* + * Read memslot_have_rmaps before rmap pointers. Hence, threads reading + * memslots_have_rmaps in any lock context are guaranteed to see the + * pointers. Pairs with smp_store_release in alloc_all_memslots_rmaps. + */ + return smp_load_acquire(&kvm->arch.memslots_have_rmaps); } #endif diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c index 2131f71577bc..aa9e77f406d9 100644 --- a/arch/x86/kvm/mmu/mmu.c +++ b/arch/x86/kvm/mmu/mmu.c @@ -3312,6 +3312,10 @@ 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) @@ -5523,9 +5527,13 @@ 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; diff --git a/arch/x86/kvm/mmu/tdp_mmu.c b/arch/x86/kvm/mmu/tdp_mmu.c index 6b6dfcdcb179..cc13e001f3de 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 a861570fcd7c..f7a7990da11d 100644 --- a/arch/x86/kvm/mmu/tdp_mmu.h +++ b/arch/x86/kvm/mmu/tdp_mmu.h @@ -81,12 +81,12 @@ 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 ddeff81f90a4..e838e999ab49 100644 --- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c @@ -10952,6 +10952,8 @@ static int memslot_rmap_alloc(struct kvm_memory_slot *slot, int lpages = gfn_to_index(slot->base_gfn + npages - 1, slot->base_gfn, level) + 1; + WARN_ON(slot->arch.rmap[i]); + slot->arch.rmap[i] = kvcalloc(lpages, sz, GFP_KERNEL_ACCOUNT); if (!slot->arch.rmap[i]) { memslot_rmap_free(slot); @@ -10962,6 +10964,50 @@ 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, i; + + /* + * Check if memslots alreday have rmaps early before acquiring + * the slots_arch_lock below. + */ + if (kvm_memslots_have_rmaps(kvm)) + return 0; + + mutex_lock(&kvm->slots_arch_lock); + + /* + * Read memslots_have_rmaps again, under the slots arch lock, + * before allocating the rmaps + */ + if (kvm_memslots_have_rmaps(kvm)) { + mutex_unlock(&kvm->slots_arch_lock); + 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; + } + } + } + + /* + * Ensure that memslots_have_rmaps becomes true strictly after + * all the rmap pointers are set. + */ + 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) -- GitLab