Commit d501f747 authored by Ben Gardon's avatar Ben Gardon Committed by Paolo Bonzini
Browse files

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: default avatarBen Gardon <bgardon@google.com>
Message-Id: <20210518173414.450044-8-bgardon@google.com>
Signed-off-by: default avatarPaolo Bonzini <pbonzini@redhat.com>
parent e2209710

arch/x86/include/asm/kvm_host.h

+2 −0
Original line number Diff line number Diff line
@@ -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 */

arch/x86/kvm/mmu.h

+6 −1
Original line number Diff line number Diff line
@@ -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

arch/x86/kvm/mmu/mmu.c

+11 −3
Original line number Diff line number Diff line
@@ -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)
@@ -5523,8 +5527,12 @@ 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);



	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;

arch/x86/kvm/mmu/tdp_mmu.c

+4 −2
Original line number Diff line number Diff line
@@ -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,

arch/x86/kvm/mmu/tdp_mmu.h

+2 −2
Original line number Diff line number Diff line
@@ -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; }