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

[Marc Zyngier <maz@kernel.org>]

On Sun, 06 Nov 2022 21:46:19 +0000,
Gavin Shan <gshan@redhat.com> wrote:
> 
> 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') ?

No, this still needs to be per-VM.

	M.

-- 
Without deviation from the norm, progress is not possible.
_______________________________________________
kvmarm mailing list
kvmarm@lists.cs.columbia.edu
https://lists.cs.columbia.edu/mailman/listinfo/kvmarm