Commit 1af4a960 authored by Ben Gardon's avatar Ben Gardon Committed by Paolo Bonzini
Browse files

KVM: x86/mmu: Yield in TDU MMU iter even if no SPTES changed 



Given certain conditions, some TDP MMU functions may not yield
reliably / frequently enough. For example, if a paging structure was
very large but had few, if any writable entries, wrprot_gfn_range
could traverse many entries before finding a writable entry and yielding
because the check for yielding only happens after an SPTE is modified.

Fix this issue by moving the yield to the beginning of the loop.

Fixes: a6a0b05d ("kvm: x86/mmu: Support dirty logging for the TDP MMU")
Reviewed-by: default avatarPeter Feiner <pfeiner@google.com>
Signed-off-by: default avatarBen Gardon <bgardon@google.com>

Message-Id: <20210202185734.1680553-15-bgardon@google.com>
Signed-off-by: default avatarPaolo Bonzini <pbonzini@redhat.com>
parent ed5e484b

arch/x86/kvm/mmu/tdp_mmu.c

+22 −10
Original line number Diff line number Diff line
@@ -501,6 +501,12 @@ static bool zap_gfn_range(struct kvm *kvm, struct kvm_mmu_page *root, 
	bool flush_needed = false;



	tdp_root_for_each_pte(iter, root, start, end) {

		if (can_yield &&

		    tdp_mmu_iter_cond_resched(kvm, &iter, flush_needed)) {

			flush_needed = false;

			continue;

		}



		if (!is_shadow_present_pte(iter.old_spte))

			continue;
@@ -515,9 +521,7 @@ static bool zap_gfn_range(struct kvm *kvm, struct kvm_mmu_page *root, 
			continue;



		tdp_mmu_set_spte(kvm, &iter, 0);



		flush_needed = !(can_yield &&

				 tdp_mmu_iter_cond_resched(kvm, &iter, true));

		flush_needed = true;

	}

	return flush_needed;

}
@@ -880,6 +884,9 @@ static bool wrprot_gfn_range(struct kvm *kvm, struct kvm_mmu_page *root, 


	for_each_tdp_pte_min_level(iter, root->spt, root->role.level,

				   min_level, start, end) {

		if (tdp_mmu_iter_cond_resched(kvm, &iter, false))

			continue;



		if (!is_shadow_present_pte(iter.old_spte) ||

		    !is_last_spte(iter.old_spte, iter.level))

			continue;
@@ -888,8 +895,6 @@ static bool wrprot_gfn_range(struct kvm *kvm, struct kvm_mmu_page *root, 


		tdp_mmu_set_spte_no_dirty_log(kvm, &iter, new_spte);

		spte_set = true;



		tdp_mmu_iter_cond_resched(kvm, &iter, false);

	}

	return spte_set;

}
@@ -933,6 +938,9 @@ static bool clear_dirty_gfn_range(struct kvm *kvm, struct kvm_mmu_page *root, 
	bool spte_set = false;



	tdp_root_for_each_leaf_pte(iter, root, start, end) {

		if (tdp_mmu_iter_cond_resched(kvm, &iter, false))

			continue;



		if (spte_ad_need_write_protect(iter.old_spte)) {

			if (is_writable_pte(iter.old_spte))

				new_spte = iter.old_spte & ~PT_WRITABLE_MASK;
@@ -947,8 +955,6 @@ static bool clear_dirty_gfn_range(struct kvm *kvm, struct kvm_mmu_page *root, 


		tdp_mmu_set_spte_no_dirty_log(kvm, &iter, new_spte);

		spte_set = true;



		tdp_mmu_iter_cond_resched(kvm, &iter, false);

	}

	return spte_set;

}
@@ -1056,6 +1062,9 @@ static bool set_dirty_gfn_range(struct kvm *kvm, struct kvm_mmu_page *root, 
	bool spte_set = false;



	tdp_root_for_each_pte(iter, root, start, end) {

		if (tdp_mmu_iter_cond_resched(kvm, &iter, false))

			continue;



		if (!is_shadow_present_pte(iter.old_spte))

			continue;
@@ -1063,8 +1072,6 @@ static bool set_dirty_gfn_range(struct kvm *kvm, struct kvm_mmu_page *root, 


		tdp_mmu_set_spte(kvm, &iter, new_spte);

		spte_set = true;



		tdp_mmu_iter_cond_resched(kvm, &iter, false);

	}



	return spte_set;
@@ -1105,6 +1112,11 @@ static void zap_collapsible_spte_range(struct kvm *kvm, 
	bool spte_set = false;



	tdp_root_for_each_pte(iter, root, start, end) {

		if (tdp_mmu_iter_cond_resched(kvm, &iter, spte_set)) {

			spte_set = false;

			continue;

		}



		if (!is_shadow_present_pte(iter.old_spte) ||

		    !is_last_spte(iter.old_spte, iter.level))

			continue;
@@ -1116,7 +1128,7 @@ static void zap_collapsible_spte_range(struct kvm *kvm, 


		tdp_mmu_set_spte(kvm, &iter, 0);



		spte_set = !tdp_mmu_iter_cond_resched(kvm, &iter, true);

		spte_set = true;

	}



	if (spte_set)