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FAILED: patch "[PATCH] KVM: x86/mmu: Yield in TDU MMU iter even if no SPTES changed" failed to apply to 5.11-stable tree

PATCH [email protected] 1 participant 1 message Apr 3, 2021

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The patch below does not apply to the 5.11-stable tree.
If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to <[email protected]>.

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From 1af4a96025b33587ca953c7ef12a1b20c6e70412 Mon Sep 17 00:00:00 2001
From: Ben Gardon <[email protected]>
Date: Tue, 2 Feb 2021 10:57:20 -0800
Subject: [PATCH] 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 a6a0b05da9f3 ("kvm: x86/mmu: Support dirty logging for the TDP MMU")
Reviewed-by Peter Feiner <[email protected]>
Signed-off-by Ben Gardon <[email protected]>

Message-Id: <[email protected]>

Signed-off-by Paolo Bonzini <[email protected]>
arch/x86/kvm/mmu/tdp_mmu.c +22 -10
index 7cfc0639b1ef..c8a1149cb229 100644
@@ -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)