Commit 10ba2d17 authored by Gavin Shan's avatar Gavin Shan Committed by Marc Zyngier
Browse files

KVM: arm64: Don't retrieve memory slot again in page fault handler 



We needn't retrieve the memory slot again in user_mem_abort() because
the corresponding memory slot has been passed from the caller. This
would save some CPU cycles. For example, the time used to write 1GB
memory, which is backed by 2MB hugetlb pages and write-protected, is
dropped by 6.8% from 928ms to 864ms.

Signed-off-by: default avatarGavin Shan <gshan@redhat.com>
Reviewed-by: default avatarKeqian Zhu <zhukeqian1@huawei.com>
Signed-off-by: default avatarMarc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20210316041126.81860-4-gshan@redhat.com
parent c728fd4c

arch/arm64/kvm/mmu.c

+7 −2
Original line number Diff line number Diff line
@@ -843,10 +843,15 @@ static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa, 
	 * unmapped afterwards, the call to kvm_unmap_hva will take it away

	 * from us again properly. This smp_rmb() interacts with the smp_wmb()

	 * in kvm_mmu_notifier_invalidate_<page|range_end>.

	 *

	 * Besides, __gfn_to_pfn_memslot() instead of gfn_to_pfn_prot() is

	 * used to avoid unnecessary overhead introduced to locate the memory

	 * slot because it's always fixed even @gfn is adjusted for huge pages.

	 */

	smp_rmb();



	pfn = gfn_to_pfn_prot(kvm, gfn, write_fault, &writable);

	pfn = __gfn_to_pfn_memslot(memslot, gfn, false, NULL,

				   write_fault, &writable, NULL);

	if (pfn == KVM_PFN_ERR_HWPOISON) {

		kvm_send_hwpoison_signal(hva, vma_shift);

		return 0;
@@ -912,7 +917,7 @@ static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa, 
	/* Mark the page dirty only if the fault is handled successfully */

	if (writable && !ret) {

		kvm_set_pfn_dirty(pfn);

		mark_page_dirty(kvm, gfn);

		mark_page_dirty_in_slot(kvm, memslot, gfn);

	}



out_unlock: