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KVM: x86/mmu: Batch zap MMU pages when recycling oldest pages

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Collect MMU pages for zapping in a loop when making MMU pages available,
and skip over active roots when doing so as zapping an active root can
never immediately free up a page.  Batching the zapping avoids multiple
remote TLB flushes and remedies the issue where the loop would bail
early if an active root was encountered.

Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
Message-Id: <20200623193542.7554-3-sean.j.christopherson@intel.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
This commit is contained in:
Sean Christopherson 2020-06-23 12:35:40 -07:00 • committed by Paolo Bonzini
parent f95eec9bed
commit 6b82ef2c9c
1 changed files with 39 additions and 13 deletions
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52
arch/x86/kvm/mmu/mmu.c
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@ -2829,20 +2829,51 @@ static bool prepare_zap_oldest_mmu_page(struct kvm *kvm,
return kvm_mmu_prepare_zap_page(kvm, sp, invalid_list); return kvm_mmu_prepare_zap_page(kvm, sp, invalid_list);
} }
static int make_mmu_pages_available(struct kvm_vcpu *vcpu) static unsigned long kvm_mmu_zap_oldest_mmu_pages(struct kvm *kvm,
unsigned long nr_to_zap)
{ {
unsigned long total_zapped = 0;
struct kvm_mmu_page *sp, *tmp;
LIST_HEAD(invalid_list); LIST_HEAD(invalid_list);
bool unstable;
int nr_zapped;
if (likely(kvm_mmu_available_pages(vcpu->kvm) >= KVM_MIN_FREE_MMU_PAGES)) if (list_empty(&kvm->arch.active_mmu_pages))
return 0; return 0;
while (kvm_mmu_available_pages(vcpu->kvm) < KVM_REFILL_PAGES) { restart:
if (!prepare_zap_oldest_mmu_page(vcpu->kvm, &invalid_list)) list_for_each_entry_safe(sp, tmp, &kvm->arch.active_mmu_pages, link) {
/*
* Don't zap active root pages, the page itself can't be freed
* and zapping it will just force vCPUs to realloc and reload.
*/
if (sp->root_count)
continue;
unstable = __kvm_mmu_prepare_zap_page(kvm, sp, &invalid_list,
&nr_zapped);
total_zapped += nr_zapped;
if (total_zapped >= nr_to_zap)
break; break;
++vcpu->kvm->stat.mmu_recycled; if (unstable)
goto restart;
} }
kvm_mmu_commit_zap_page(vcpu->kvm, &invalid_list);
kvm_mmu_commit_zap_page(kvm, &invalid_list);
kvm->stat.mmu_recycled += total_zapped;
return total_zapped;
}
static int make_mmu_pages_available(struct kvm_vcpu *vcpu)
{
unsigned long avail = kvm_mmu_available_pages(vcpu->kvm);
if (likely(avail >= KVM_MIN_FREE_MMU_PAGES))
return 0;
kvm_mmu_zap_oldest_mmu_pages(vcpu->kvm, KVM_REFILL_PAGES - avail);
if (!kvm_mmu_available_pages(vcpu->kvm)) if (!kvm_mmu_available_pages(vcpu->kvm))
return -ENOSPC; return -ENOSPC;
@ -2855,17 +2886,12 @@ static int make_mmu_pages_available(struct kvm_vcpu *vcpu)
*/ */
void kvm_mmu_change_mmu_pages(struct kvm *kvm, unsigned long goal_nr_mmu_pages) void kvm_mmu_change_mmu_pages(struct kvm *kvm, unsigned long goal_nr_mmu_pages)
{ {
LIST_HEAD(invalid_list);
spin_lock(&kvm->mmu_lock); spin_lock(&kvm->mmu_lock);
if (kvm->arch.n_used_mmu_pages > goal_nr_mmu_pages) { if (kvm->arch.n_used_mmu_pages > goal_nr_mmu_pages) {
/* Need to free some mmu pages to achieve the goal. */ kvm_mmu_zap_oldest_mmu_pages(kvm, kvm->arch.n_used_mmu_pages -
while (kvm->arch.n_used_mmu_pages > goal_nr_mmu_pages) goal_nr_mmu_pages);
if (!prepare_zap_oldest_mmu_page(kvm, &invalid_list))
break;
kvm_mmu_commit_zap_page(kvm, &invalid_list);
goal_nr_mmu_pages = kvm->arch.n_used_mmu_pages; goal_nr_mmu_pages = kvm->arch.n_used_mmu_pages;
} }