Commit 14881998 authored by Ben Gardon's avatar Ben Gardon Committed by Paolo Bonzini
Browse files

kvm: x86/mmu: Support disabling dirty logging for the tdp MMU 

Dirty logging ultimately breaks down MMU mappings to 4k granularity.
When dirty logging is no longer needed, these granaular mappings
represent a useless performance penalty. When dirty logging is disabled,
search the paging structure for mappings that could be re-constituted
into a large page mapping. Zap those mappings so that they can be
faulted in again at a higher mapping level.

Tested by running kvm-unit-tests and KVM selftests on an Intel Haswell
machine. This series introduced no new failures.

This series can be viewed in Gerrit at:
	https://linux-review.googlesource.com/c/virt/kvm/kvm/+/2538



Signed-off-by: default avatarBen Gardon <bgardon@google.com>
Message-Id: <20201014182700.2888246-17-bgardon@google.com>
Signed-off-by: default avatarPaolo Bonzini <pbonzini@redhat.com>
parent a6a0b05d

arch/x86/kvm/mmu/mmu.c

+3 −0
Original line number Diff line number Diff line
@@ -5544,6 +5544,9 @@ void kvm_mmu_zap_collapsible_sptes(struct kvm *kvm, 
	spin_lock(&kvm->mmu_lock);

	slot_handle_leaf(kvm, (struct kvm_memory_slot *)memslot,

			 kvm_mmu_zap_collapsible_spte, true);



	if (kvm->arch.tdp_mmu_enabled)

		kvm_tdp_mmu_zap_collapsible_sptes(kvm, memslot);

	spin_unlock(&kvm->mmu_lock);

}

arch/x86/kvm/mmu/tdp_mmu.c

+58 −0
Original line number Diff line number Diff line
@@ -1020,3 +1020,61 @@ bool kvm_tdp_mmu_slot_set_dirty(struct kvm *kvm, struct kvm_memory_slot *slot) 
	return spte_set;

}



/*

 * Clear non-leaf entries (and free associated page tables) which could

 * be replaced by large mappings, for GFNs within the slot.

 */

static void zap_collapsible_spte_range(struct kvm *kvm,

				       struct kvm_mmu_page *root,

				       gfn_t start, gfn_t end)

{

	struct tdp_iter iter;

	kvm_pfn_t pfn;

	bool spte_set = false;



	tdp_root_for_each_pte(iter, root, start, end) {

		if (!is_shadow_present_pte(iter.old_spte) ||

		    is_last_spte(iter.old_spte, iter.level))

			continue;



		pfn = spte_to_pfn(iter.old_spte);

		if (kvm_is_reserved_pfn(pfn) ||

		    !PageTransCompoundMap(pfn_to_page(pfn)))

			continue;



		tdp_mmu_set_spte(kvm, &iter, 0);



		spte_set = tdp_mmu_iter_flush_cond_resched(kvm, &iter);

	}



	if (spte_set)

		kvm_flush_remote_tlbs(kvm);

}



/*

 * Clear non-leaf entries (and free associated page tables) which could

 * be replaced by large mappings, for GFNs within the slot.

 */

void kvm_tdp_mmu_zap_collapsible_sptes(struct kvm *kvm,

				       const struct kvm_memory_slot *slot)

{

	struct kvm_mmu_page *root;

	int root_as_id;



	for_each_tdp_mmu_root(kvm, root) {

		root_as_id = kvm_mmu_page_as_id(root);

		if (root_as_id != slot->as_id)

			continue;



		/*

		 * Take a reference on the root so that it cannot be freed if

		 * this thread releases the MMU lock and yields in this loop.

		 */

		kvm_mmu_get_root(kvm, root);



		zap_collapsible_spte_range(kvm, root, slot->base_gfn,

					   slot->base_gfn + slot->npages);



		kvm_mmu_put_root(kvm, root);

	}

}

arch/x86/kvm/mmu/tdp_mmu.h

+2 −0
Original line number Diff line number Diff line
@@ -38,4 +38,6 @@ void kvm_tdp_mmu_clear_dirty_pt_masked(struct kvm *kvm, 
				       gfn_t gfn, unsigned long mask,

				       bool wrprot);

bool kvm_tdp_mmu_slot_set_dirty(struct kvm *kvm, struct kvm_memory_slot *slot);

void kvm_tdp_mmu_zap_collapsible_sptes(struct kvm *kvm,

				       const struct kvm_memory_slot *slot);

#endif /* __KVM_X86_MMU_TDP_MMU_H */

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