Commit f5756029 authored by Maciej S. Szmigiero's avatar Maciej S. Szmigiero Committed by Paolo Bonzini
Browse files

KVM: x86: Use nr_memslot_pages to avoid traversing the memslots array 



There is no point in recalculating from scratch the total number of pages
in all memslots each time a memslot is created or deleted.  Use KVM's
cached nr_memslot_pages to compute the default max number of MMU pages.

Note that even with nr_memslot_pages capped at ULONG_MAX we can't safely
multiply it by KVM_PERMILLE_MMU_PAGES (20) since this operation can
possibly overflow an unsigned long variable.

Write this "* 20 / 1000" operation as "/ 50" instead to avoid such
overflow.

Signed-off-by: default avatarMaciej S. Szmigiero <maciej.szmigiero@oracle.com>
[sean: use common KVM field and rework changelog accordingly]
Reviewed-by: default avatarSean Christopherson <seanjc@google.com>
Message-Id: <d14c5a24535269606675437d5602b7dac4ad8c0e.1638817640.git.maciej.szmigiero@oracle.com>
parent e0c2b633

arch/x86/include/asm/kvm_host.h

+1 −2
Original line number Diff line number Diff line
@@ -135,7 +135,7 @@ 
#define KVM_HPAGE_MASK(x)	(~(KVM_HPAGE_SIZE(x) - 1))

#define KVM_PAGES_PER_HPAGE(x)	(KVM_HPAGE_SIZE(x) / PAGE_SIZE)



#define KVM_PERMILLE_MMU_PAGES 20

#define KVM_MEMSLOT_PAGES_TO_MMU_PAGES_RATIO 50

#define KVM_MIN_ALLOC_MMU_PAGES 64UL

#define KVM_MMU_HASH_SHIFT 12

#define KVM_NUM_MMU_PAGES (1 << KVM_MMU_HASH_SHIFT)
@@ -1592,7 +1592,6 @@ void kvm_mmu_slot_leaf_clear_dirty(struct kvm *kvm, 
				   const struct kvm_memory_slot *memslot);

void kvm_mmu_zap_all(struct kvm *kvm);

void kvm_mmu_invalidate_mmio_sptes(struct kvm *kvm, u64 gen);

unsigned long kvm_mmu_calculate_default_mmu_pages(struct kvm *kvm);

void kvm_mmu_change_mmu_pages(struct kvm *kvm, unsigned long kvm_nr_mmu_pages);



int load_pdptrs(struct kvm_vcpu *vcpu, struct kvm_mmu *mmu, unsigned long cr3);

arch/x86/kvm/mmu/mmu.c

+0 −24
Original line number Diff line number Diff line
@@ -6150,30 +6150,6 @@ int kvm_mmu_module_init(void) 
	return ret;

}



/*

 * Calculate mmu pages needed for kvm.

 */

unsigned long kvm_mmu_calculate_default_mmu_pages(struct kvm *kvm)

{

	unsigned long nr_mmu_pages;

	unsigned long nr_pages = 0;

	struct kvm_memslots *slots;

	struct kvm_memory_slot *memslot;

	int i;



	for (i = 0; i < KVM_ADDRESS_SPACE_NUM; i++) {

		slots = __kvm_memslots(kvm, i);



		kvm_for_each_memslot(memslot, slots)

			nr_pages += memslot->npages;

	}



	nr_mmu_pages = nr_pages * KVM_PERMILLE_MMU_PAGES / 1000;

	nr_mmu_pages = max(nr_mmu_pages, KVM_MIN_ALLOC_MMU_PAGES);



	return nr_mmu_pages;

}



void kvm_mmu_destroy(struct kvm_vcpu *vcpu)

{

	kvm_mmu_unload(vcpu);

arch/x86/kvm/x86.c

+7 −3
Original line number Diff line number Diff line
@@ -11784,9 +11784,13 @@ void kvm_arch_commit_memory_region(struct kvm *kvm, 
				enum kvm_mr_change change)

{

	if (!kvm->arch.n_requested_mmu_pages &&

	    (change == KVM_MR_CREATE || change == KVM_MR_DELETE))

		kvm_mmu_change_mmu_pages(kvm,

				kvm_mmu_calculate_default_mmu_pages(kvm));

	    (change == KVM_MR_CREATE || change == KVM_MR_DELETE)) {

		unsigned long nr_mmu_pages;



		nr_mmu_pages = kvm->nr_memslot_pages / KVM_MEMSLOT_PAGES_TO_MMU_PAGES_RATIO;

		nr_mmu_pages = max(nr_mmu_pages, KVM_MIN_ALLOC_MMU_PAGES);

		kvm_mmu_change_mmu_pages(kvm, nr_mmu_pages);

	}



	kvm_mmu_slot_apply_flags(kvm, old, new, change);