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

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Hi Marc,

On 11/6/22 11:50 PM, Marc Zyngier wrote:
On Fri, 04 Nov 2022 23:40:46 +0000,
Gavin Shan <gshan@xxxxxxxxxx> 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@xxxxxxxxxx>
---
  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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