linux-kernel - Re: [PATCH] KVM: riscv: Support enabling dirty log gradually in small chunks

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Message-ID: <CAAhSdy01XGT6psT+3EgHbgyyOhuXP63Zv1K2acvDZKD0LxxQ=w@mail.gmail.com>
Date: Fri, 7 Nov 2025 16:33:48 +0530
From: Anup Patel <anup@...infault.org>
To: dayss1224@...il.com
Cc: ajones@...tanamicro.com, atishp@...shpatra.org, paul.walmsley@...ive.com, 
	palmer@...belt.com, linux-kernel@...r.kernel.org, 
	linux-riscv@...ts.infradead.org, kvm@...r.kernel.org, 
	kvm-riscv@...ts.infradead.org, Quan Zhou <zhouquan@...as.ac.cn>
Subject: Re: [PATCH] KVM: riscv: Support enabling dirty log gradually in small chunks

On Mon, Nov 3, 2025 at 11:58 AM <dayss1224@...il.com> wrote:
>
> From: Dong Yang <dayss1224@...il.com>
>
> There is already support of enabling dirty log gradually in small chunks
> for x86 in commit 3c9bd4006bfc ("KVM: x86: enable dirty log gradually in
> small chunks") and c862626 ("KVM: arm64: Support enabling dirty log
> gradually in small chunks"). This adds support for riscv.
>
> x86 and arm64 writes protect both huge pages and normal pages now, so
> riscv protect also protects both huge pages and normal pages.
>
> On a nested virtualization setup (RISC-V KVM running inside a QEMU VM
> on an [Intel® Core™ i5-12500H] host), I did some tests with a 2G Linux
> VM using different backing page sizes. The time taken for
> memory_global_dirty_log_start in the L2 QEMU is listed below:
>
> Page Size      Before    After Optimization
>   4K            4490.23ms         31.94ms
>   2M             48.97ms          45.46ms
>   1G             28.40ms          30.93ms
>
> Signed-off-by: Quan Zhou <zhouquan@...as.ac.cn>
> Signed-off-by: Dong Yang <dayss1224@...il.com>

LGTM.

Reviewed-by: Anup Patel <anup@...infault.org>

Queued this patch for Linux-6.19

Thanks,
Anup


> ---
>  Documentation/virt/kvm/api.rst    | 2 +-
>  arch/riscv/include/asm/kvm_host.h | 3 +++
>  arch/riscv/kvm/mmu.c              | 5 ++++-
>  3 files changed, 8 insertions(+), 2 deletions(-)
>
> diff --git a/Documentation/virt/kvm/api.rst b/Documentation/virt/kvm/api.rst
> index 57061fa29e6a..3b621c3ae67c 100644
> --- a/Documentation/virt/kvm/api.rst
> +++ b/Documentation/virt/kvm/api.rst
> @@ -8028,7 +8028,7 @@ will be initialized to 1 when created.  This also improves performance because
>  dirty logging can be enabled gradually in small chunks on the first call
>  to KVM_CLEAR_DIRTY_LOG.  KVM_DIRTY_LOG_INITIALLY_SET depends on
>  KVM_DIRTY_LOG_MANUAL_PROTECT_ENABLE (it is also only available on
> -x86 and arm64 for now).
> +x86, arm64 and riscv for now).
>
>  KVM_CAP_MANUAL_DIRTY_LOG_PROTECT2 was previously available under the name
>  KVM_CAP_MANUAL_DIRTY_LOG_PROTECT, but the implementation had bugs that make
> diff --git a/arch/riscv/include/asm/kvm_host.h b/arch/riscv/include/asm/kvm_host.h
> index 4d794573e3db..848b63f87001 100644
> --- a/arch/riscv/include/asm/kvm_host.h
> +++ b/arch/riscv/include/asm/kvm_host.h
> @@ -59,6 +59,9 @@
>                                          BIT(IRQ_VS_TIMER) | \
>                                          BIT(IRQ_VS_EXT))
>
> +#define KVM_DIRTY_LOG_MANUAL_CAPS   (KVM_DIRTY_LOG_MANUAL_PROTECT_ENABLE | \
> +       KVM_DIRTY_LOG_INITIALLY_SET)
> +
>  struct kvm_vm_stat {
>         struct kvm_vm_stat_generic generic;
>  };
> diff --git a/arch/riscv/kvm/mmu.c b/arch/riscv/kvm/mmu.c
> index 525fb5a330c0..a194eee256d8 100644
> --- a/arch/riscv/kvm/mmu.c
> +++ b/arch/riscv/kvm/mmu.c
> @@ -161,8 +161,11 @@ void kvm_arch_commit_memory_region(struct kvm *kvm,
>          * allocated dirty_bitmap[], dirty pages will be tracked while
>          * the memory slot is write protected.
>          */
> -       if (change != KVM_MR_DELETE && new->flags & KVM_MEM_LOG_DIRTY_PAGES)
> +       if (change != KVM_MR_DELETE && new->flags & KVM_MEM_LOG_DIRTY_PAGES) {
> +               if (kvm_dirty_log_manual_protect_and_init_set(kvm))
> +                       return;
>                 mmu_wp_memory_region(kvm, new->id);
> +       }
>  }
>
>  int kvm_arch_prepare_memory_region(struct kvm *kvm,
> --
> 2.34.1
>