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RISC-V: KVM: Add the eager_page_split module parameter

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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 <wang.yechao255@zte.com.cn>
Reviewed-by: Anup Patel <anup@brainfault.org>
Link: https://lore.kernel.org/r/20260731091215.1549430-6-wang.yechao255@zte.com.cn
Signed-off-by: Anup Patel <anup@brainfault.org>
This commit is contained in:
Wang Yechao
2026-07-31 17:12:10 +08:00
committed by Anup Patel
parent c67573b37c
commit 98a1e65ca4
2 changed files with 15 additions and 5 deletions
Download Patch File Download Diff File Expand all files Collapse all files

7
Documentation/admin-guide/kernel-parameters.txt
View File

@@ -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).

13
arch/riscv/kvm/mmu.c
View File

@@ -16,6 +16,9 @@
#include <asm/kvm_mmu.h>
#include <asm/kvm_nacl.h>
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);
}
}