Re: [PATCH v8 4/7] KVM: arm64: Enable ring-based dirty memory tracking

[Marc Zyngier <maz@kernel.org>]

On Fri, 04 Nov 2022 23:40:46 +0000,
Gavin Shan <gshan@redhat.com> wrote:
> 
> Enable ring-based dirty memory tracking on arm64 by selecting
> CONFIG_HAVE_KVM_DIRTY_{RING_ACQ_REL, RING_WITH_BITMAP} and providing
> the ring buffer's physical page offset (KVM_DIRTY_LOG_PAGE_OFFSET).
> 
> Besides, helper kvm_vgic_save_its_tables_in_progress() is added to
> indicate if vgic/its tables are being saved or not. The helper is used
> in ARM64's kvm_arch_allow_write_without_running_vcpu() to keep the
> site of saving vgic/its tables out of no-running-vcpu radar.
> 
> Signed-off-by: Gavin Shan <gshan@redhat.com>
> ---
>  Documentation/virt/kvm/api.rst     |  2 +-
>  arch/arm64/include/uapi/asm/kvm.h  |  1 +
>  arch/arm64/kvm/Kconfig             |  2 ++
>  arch/arm64/kvm/arm.c               |  3 +++
>  arch/arm64/kvm/mmu.c               | 15 +++++++++++++++
>  arch/arm64/kvm/vgic/vgic-its.c     |  3 +++
>  arch/arm64/kvm/vgic/vgic-mmio-v3.c |  7 +++++++
>  include/kvm/arm_vgic.h             |  2 ++
>  8 files changed, 34 insertions(+), 1 deletion(-)
> 
> diff --git a/Documentation/virt/kvm/api.rst b/Documentation/virt/kvm/api.rst
> index 2ec32bd41792..2fc68f684ad8 100644
> --- a/Documentation/virt/kvm/api.rst
> +++ b/Documentation/virt/kvm/api.rst
> @@ -7921,7 +7921,7 @@ regardless of what has actually been exposed through the CPUID leaf.
>  8.29 KVM_CAP_DIRTY_LOG_RING/KVM_CAP_DIRTY_LOG_RING_ACQ_REL
>  ----------------------------------------------------------
>  
> -:Architectures: x86
> +:Architectures: x86, arm64
>  :Parameters: args[0] - size of the dirty log ring
>  
>  KVM is capable of tracking dirty memory using ring buffers that are
> diff --git a/arch/arm64/include/uapi/asm/kvm.h b/arch/arm64/include/uapi/asm/kvm.h
> index 316917b98707..a7a857f1784d 100644
> --- a/arch/arm64/include/uapi/asm/kvm.h
> +++ b/arch/arm64/include/uapi/asm/kvm.h
> @@ -43,6 +43,7 @@
>  #define __KVM_HAVE_VCPU_EVENTS
>  
>  #define KVM_COALESCED_MMIO_PAGE_OFFSET 1
> +#define KVM_DIRTY_LOG_PAGE_OFFSET 64
>  
>  #define KVM_REG_SIZE(id)						\
>  	(1U << (((id) & KVM_REG_SIZE_MASK) >> KVM_REG_SIZE_SHIFT))
> diff --git a/arch/arm64/kvm/Kconfig b/arch/arm64/kvm/Kconfig
> index 815cc118c675..066b053e9eb9 100644
> --- a/arch/arm64/kvm/Kconfig
> +++ b/arch/arm64/kvm/Kconfig
> @@ -32,6 +32,8 @@ menuconfig KVM
>  	select KVM_VFIO
>  	select HAVE_KVM_EVENTFD
>  	select HAVE_KVM_IRQFD
> +	select HAVE_KVM_DIRTY_RING_ACQ_REL
> +	select HAVE_KVM_DIRTY_RING_WITH_BITMAP
>  	select HAVE_KVM_MSI
>  	select HAVE_KVM_IRQCHIP
>  	select HAVE_KVM_IRQ_ROUTING
> diff --git a/arch/arm64/kvm/arm.c b/arch/arm64/kvm/arm.c
> index 94d33e296e10..6b097605e38c 100644
> --- a/arch/arm64/kvm/arm.c
> +++ b/arch/arm64/kvm/arm.c
> @@ -746,6 +746,9 @@ static int check_vcpu_requests(struct kvm_vcpu *vcpu)
>  
>  		if (kvm_check_request(KVM_REQ_SUSPEND, vcpu))
>  			return kvm_vcpu_suspend(vcpu);
> +
> +		if (kvm_dirty_ring_check_request(vcpu))
> +			return 0;
>  	}
>  
>  	return 1;
> diff --git a/arch/arm64/kvm/mmu.c b/arch/arm64/kvm/mmu.c
> index 60ee3d9f01f8..fbeb55e45f53 100644
> --- a/arch/arm64/kvm/mmu.c
> +++ b/arch/arm64/kvm/mmu.c
> @@ -932,6 +932,21 @@ void kvm_arch_mmu_enable_log_dirty_pt_masked(struct kvm *kvm,
>  	kvm_mmu_write_protect_pt_masked(kvm, slot, gfn_offset, mask);
>  }
>  
> +/*
> + * kvm_arch_allow_write_without_running_vcpu - allow writing guest memory
> + * without the running VCPU when dirty ring is enabled.
> + *
> + * The running VCPU is required to track dirty guest pages when dirty ring
> + * is enabled. Otherwise, the backup bitmap should be used to track the
> + * dirty guest pages. When vgic/its tables are being saved, the backup
> + * bitmap is used to track the dirty guest pages due to the missed running
> + * VCPU in the period.
> + */
> +bool kvm_arch_allow_write_without_running_vcpu(struct kvm *kvm)
> +{
> +	return kvm_vgic_save_its_tables_in_progress(kvm);

I don't think we need the extra level of abstraction here. Just return
kvm->arch.vgic.save_its_tables_in_progress and be done with it.

You can also move the helper to the vgic-its code since they are
closely related for now.

Thanks,

	M.

-- 
Without deviation from the norm, progress is not possible.
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