From 98a1e65ca455d6366ca171dacdf1e3737f6fea14 Mon Sep 17 00:00:00 2001 From: Wang Yechao Date: Fri, 31 Jul 2026 17:12:10 +0800 Subject: [PATCH] RISC-V: KVM: Add the eager_page_split module parameter 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 Reviewed-by: Anup Patel Link: https://lore.kernel.org/r/20260731091215.1549430-6-wang.yechao255@zte.com.cn Signed-off-by: Anup Patel --- Documentation/admin-guide/kernel-parameters.txt | 7 +++++-- arch/riscv/kvm/mmu.c | 13 ++++++++++--- 2 files changed, 15 insertions(+), 5 deletions(-) diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt index b5493a7f8f22..d78eda7ee23a 100644 --- a/Documentation/admin-guide/kernel-parameters.txt +++ b/Documentation/admin-guide/kernel-parameters.txt @@ -3047,7 +3047,7 @@ Kernel parameters Default is 0 (don't ignore, but inject #GP) kvm.eager_page_split= - [KVM,X86] Controls whether or not KVM will try to + [KVM,X86,RISCV] Controls whether or not KVM will try to proactively split all huge pages during dirty logging. Eager page splitting reduces interruptions to vCPU execution by eliminating the write-protection faults @@ -3067,7 +3067,10 @@ Kernel parameters the KVM_CLEAR_DIRTY ioctl, and only for the pages being cleared. - Eager page splitting is only supported when kvm.tdp_mmu=Y. + On x86, eager page splitting is only supported when + kvm.tdp_mmu=Y. + + On RISCV, eager page splitting is supported by default. Default is Y (on). diff --git a/arch/riscv/kvm/mmu.c b/arch/riscv/kvm/mmu.c index 9ae10f5b2984..154f3afaf1c9 100644 --- a/arch/riscv/kvm/mmu.c +++ b/arch/riscv/kvm/mmu.c @@ -16,6 +16,9 @@ #include #include +static 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); @@ -168,8 +171,10 @@ 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)) - mmu_split_huge_pages(&gstage, start, end); + if (kvm_dirty_log_manual_protect_and_init_set(kvm)) { + if (READ_ONCE(eager_page_split)) + mmu_split_huge_pages(&gstage, start, end); + } /* * Remote TLB flush is not needed here since callers of @@ -244,7 +249,9 @@ 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); - mmu_split_memory_region(kvm, new->id); + + if (READ_ONCE(eager_page_split)) + mmu_split_memory_region(kvm, new->id); } }