[PATCH 4/4] RISC-V: KVM: Add the eager_page_split module parameter

From: Wang Yechao <[email protected]>

Add an eager_page_split module parameter for RISC-V KVM, following
the same approach as on x86. This parameter controls whether eager
page splitting is enabled. The default value is on.

When eager page splitting is enabled, KVM proactively splits large
pages (huge pages) into smaller pages when needed for dirty logging
or other operations. Disabling it can be beneficial for VM workloads
that rarely perform writes, or that only write to a small region of
memory, as it allows huge pages to remain intact for read accesses.

Signed-off-by: Wang Yechao <[email protected]>
---
 arch/riscv/kvm/mmu.c | 13 ++++++++++---
 1 file changed, 10 insertions(+), 3 deletions(-)

diff --git a/arch/riscv/kvm/mmu.c b/arch/riscv/kvm/mmu.c
index 2cdea3e3ed4b..2af03c48aff3 100644
--- a/arch/riscv/kvm/mmu.c
+++ b/arch/riscv/kvm/mmu.c
@@ -16,6 +16,9 @@
 #include <asm/kvm_mmu.h>
 #include <asm/kvm_nacl.h>

+bool __read_mostly eager_page_split = true;
+module_param(eager_page_split, bool, 0644);
+
 static void mmu_wp_memory_region(struct kvm *kvm, int slot)
 {
 	struct kvm_memslots *slots = kvm_memslots(kvm);
@@ -148,8 +151,10 @@ void kvm_arch_mmu_enable_log_dirty_pt_masked(struct kvm *kvm,

 	kvm_riscv_gstage_wp_range(&gstage, start, end);

-	if (kvm_dirty_log_manual_protect_and_init_set(kvm))
-		kvm_riscv_split_huge_pages(&gstage, start, end, true);
+	if (kvm_dirty_log_manual_protect_and_init_set(kvm)) {
+		if (READ_ONCE(eager_page_split))
+			kvm_riscv_split_huge_pages(&gstage, start, end, true);
+	}
 }

 void kvm_arch_sync_dirty_log(struct kvm *kvm, struct kvm_memory_slot *memslot)
@@ -214,7 +219,9 @@ void kvm_arch_commit_memory_region(struct kvm *kvm,
 		if (kvm_dirty_log_manual_protect_and_init_set(kvm))
 			return;
 		mmu_wp_memory_region(kvm, new->id);
-		kvm_riscv_split_memory_region(kvm, new->id);
+
+		if (READ_ONCE(eager_page_split))
+			kvm_riscv_split_memory_region(kvm, new->id);
 	}
 }

-- 
2.27.0

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