linux-kernel - [PATCH v3 2/3] KVM: Skip invoking shared memory handler for entirely private GFN ranges

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Message-ID: <20250822080235.27274-1-yan.y.zhao@intel.com>
Date: Fri, 22 Aug 2025 16:02:34 +0800
From: Yan Zhao <yan.y.zhao@...el.com>
To: pbonzini@...hat.com,
	seanjc@...gle.com
Cc: peterx@...hat.com,
	rick.p.edgecombe@...el.com,
	linux-kernel@...r.kernel.org,
	kvm@...r.kernel.org,
	Yan Zhao <yan.y.zhao@...el.com>
Subject: [PATCH v3 2/3] KVM: Skip invoking shared memory handler for entirely private GFN ranges

When a GFN range is entirely private, it's unnecessary for
kvm_handle_hva_range() to invoke handlers for the GFN range, because
1) the gfn_range.attr_filter for the handler is KVM_FILTER_SHARED, which
   is for shared mappings only;
2) KVM has already zapped all shared mappings before setting the memory
   attribute to private.

This can avoid unnecessary zaps on private mappings for VMs of type
KVM_X86_SW_PROTECTED_VM, e.g., during auto numa balancing scans of VMAs.

Signed-off-by: Yan Zhao <yan.y.zhao@...el.com>
---
 virt/kvm/kvm_main.c | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index f769d1dccc21..e615ad405ce4 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -620,6 +620,17 @@ static __always_inline kvm_mn_ret_t kvm_handle_hva_range(struct kvm *kvm,
 			gfn_range.slot = slot;
 			gfn_range.lockless = range->lockless;
 
+#ifdef CONFIG_KVM_GENERIC_MEMORY_ATTRIBUTES
+			/*
+			 * If GFN range are all private, no need to invoke the
+			 * handler.
+			 */
+			if (kvm_range_has_memory_attributes(kvm, gfn_range.start,
+							    gfn_range.end, ~0,
+							    KVM_MEMORY_ATTRIBUTE_PRIVATE))
+				continue;
+#endif
+
 			if (!r.found_memslot) {
 				r.found_memslot = true;
 				if (!range->lockless) {
-- 
2.43.2