[PATCH 1/2] RISC-V: KVM: Enable ring-based dirty memory tracking

[Anup Patel]

On Fri, Jun 13, 2025 at 5:08 PM <zhouquan at iscas.ac.cn> wrote:
>
> From: Quan Zhou <zhouquan at iscas.ac.cn>
>
> Enable ring-based dirty memory tracking on riscv:
>
> - Enable CONFIG_HAVE_KVM_DIRTY_RING_ACQ_REL as riscv is weakly
>   ordered.
> - Set KVM_DIRTY_LOG_PAGE_OFFSET for the ring buffer's physical page
>   offset.
> - Add a check to kvm_vcpu_kvm_riscv_check_vcpu_requests for checking
>   whether the dirty ring is soft full.
>
> To handle vCPU requests that cause exits to userspace, modified the
> `kvm_riscv_check_vcpu_requests` to return a value (currently only
> returns 0 or 1).
>
> Signed-off-by: Quan Zhou <zhouquan at iscas.ac.cn>

LGTM.

Reviewed-by: Anup Patel <anup at brainfault.org>

Queued this patch for Linux-6.17

Thanks,
Anup

> ---
>  Documentation/virt/kvm/api.rst    |  2 +-
>  arch/riscv/include/uapi/asm/kvm.h |  1 +
>  arch/riscv/kvm/Kconfig            |  1 +
>  arch/riscv/kvm/vcpu.c             | 18 ++++++++++++++++--
>  4 files changed, 19 insertions(+), 3 deletions(-)
>
> diff --git a/Documentation/virt/kvm/api.rst b/Documentation/virt/kvm/api.rst
> index 1bd2d42e6424..5de0fbfe2fc0 100644
> --- a/Documentation/virt/kvm/api.rst
> +++ b/Documentation/virt/kvm/api.rst
> @@ -8316,7 +8316,7 @@ core crystal clock frequency, if a non-zero CPUID 0x15 is exposed to the guest.
>  7.36 KVM_CAP_DIRTY_LOG_RING/KVM_CAP_DIRTY_LOG_RING_ACQ_REL
>  ----------------------------------------------------------
>
> -:Architectures: x86, arm64
> +:Architectures: x86, arm64, riscv
>  :Type: vm
>  :Parameters: args[0] - size of the dirty log ring
>
> diff --git a/arch/riscv/include/uapi/asm/kvm.h b/arch/riscv/include/uapi/asm/kvm.h
> index 5f59fd226cc5..ef27d4289da1 100644
> --- a/arch/riscv/include/uapi/asm/kvm.h
> +++ b/arch/riscv/include/uapi/asm/kvm.h
> @@ -18,6 +18,7 @@
>  #define __KVM_HAVE_IRQ_LINE
>
>  #define KVM_COALESCED_MMIO_PAGE_OFFSET 1
> +#define KVM_DIRTY_LOG_PAGE_OFFSET 64
>
>  #define KVM_INTERRUPT_SET      -1U
>  #define KVM_INTERRUPT_UNSET    -2U
> diff --git a/arch/riscv/kvm/Kconfig b/arch/riscv/kvm/Kconfig
> index 704c2899197e..5a62091b0809 100644
> --- a/arch/riscv/kvm/Kconfig
> +++ b/arch/riscv/kvm/Kconfig
> @@ -25,6 +25,7 @@ config KVM
>         select HAVE_KVM_MSI
>         select HAVE_KVM_VCPU_ASYNC_IOCTL
>         select HAVE_KVM_READONLY_MEM
> +       select HAVE_KVM_DIRTY_RING_ACQ_REL
>         select KVM_COMMON
>         select KVM_GENERIC_DIRTYLOG_READ_PROTECT
>         select KVM_GENERIC_HARDWARE_ENABLING
> diff --git a/arch/riscv/kvm/vcpu.c b/arch/riscv/kvm/vcpu.c
> index e0a01af426ff..0502125efb30 100644
> --- a/arch/riscv/kvm/vcpu.c
> +++ b/arch/riscv/kvm/vcpu.c
> @@ -690,7 +690,14 @@ void kvm_arch_vcpu_put(struct kvm_vcpu *vcpu)
>         }
>  }
>
> -static void kvm_riscv_check_vcpu_requests(struct kvm_vcpu *vcpu)
> +/**
> + * check_vcpu_requests - check and handle pending vCPU requests
> + * @vcpu:      the VCPU pointer
> + *
> + * Return: 1 if we should enter the guest
> + *         0 if we should exit to userspace
> + */
> +static int kvm_riscv_check_vcpu_requests(struct kvm_vcpu *vcpu)
>  {
>         struct rcuwait *wait = kvm_arch_vcpu_get_wait(vcpu);
>
> @@ -735,7 +742,12 @@ static void kvm_riscv_check_vcpu_requests(struct kvm_vcpu *vcpu)
>
>                 if (kvm_check_request(KVM_REQ_STEAL_UPDATE, vcpu))
>                         kvm_riscv_vcpu_record_steal_time(vcpu);
> +
> +               if (kvm_dirty_ring_check_request(vcpu))
> +                       return 0;
>         }
> +
> +       return 1;
>  }
>
>  static void kvm_riscv_update_hvip(struct kvm_vcpu *vcpu)
> @@ -917,7 +929,9 @@ int kvm_arch_vcpu_ioctl_run(struct kvm_vcpu *vcpu)
>
>                 kvm_riscv_gstage_vmid_update(vcpu);
>
> -               kvm_riscv_check_vcpu_requests(vcpu);
> +               ret = kvm_riscv_check_vcpu_requests(vcpu);
> +               if (ret <= 0)
> +                       continue;
>
>                 preempt_disable();
>
> --
> 2.34.1
>