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

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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: Maciej S. Szmigiero <maciej.szmigiero@oracle.com>
[sean: use common KVM field and rework changelog accordingly]
Reviewed-by: Sean Christopherson <seanjc@google.com>
Message-Id: <d14c5a24535269606675437d5602b7dac4ad8c0e.1638817640.git.maciej.szmigiero@oracle.com>
This commit is contained in:
Maciej S. Szmigiero 2021-12-06 20:54:24 +01:00 committed by Paolo Bonzini
parent e0c2b6338a
commit f5756029ee
3 changed files with 8 additions and 29 deletions
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3
arch/x86/include/asm/kvm_host.h
View File

@ -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);

24
arch/x86/kvm/mmu/mmu.c
View File

@ -6150,30 +6150,6 @@ out:
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);

10
arch/x86/kvm/x86.c
View File

@ -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);