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

[Gavin Shan <gshan@redhat.com>]

Hi Marc,

On 11/6/22 11:50 PM, Marc Zyngier wrote:
> 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.
> 

Ok. After kvm_arch_allow_write_without_running_vcpu() is moved to vgic-its.c,
do we need to replace 'struct vgic_dist::save_its_tables_in_progress' with
a file-scoped variant ('bool vgic_its_saving_tables') ?

Thanks,
Gavin

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