On Fri, 19 Aug 2022 01:55:57 +0100, Gavin Shan gshan@redhat.com wrote:
The ring-based dirty memory tracking has been available and enabled on x86 for a while. The feature is beneficial when the number of dirty pages is small in a checkpointing system or live migration scenario. More details can be found from fb04a1eddb1a ("KVM: X86: Implement ring-based dirty memory tracking").
This enables the ring-based dirty memory tracking on ARM64. It's notable that no extra reserved ring entries are needed on ARM64 because the huge pages are always split into base pages when page dirty tracking is enabled.
Can you please elaborate on this? Adding a per-CPU ring of course results in extra memory allocation, so there must be a subtle x86-specific detail that I'm not aware of...
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 | 1 + arch/arm64/kvm/arm.c | 8 ++++++++ 4 files changed, 11 insertions(+), 1 deletion(-)
diff --git a/Documentation/virt/kvm/api.rst b/Documentation/virt/kvm/api.rst index abd7c32126ce..19fa1ac017ed 100644 --- a/Documentation/virt/kvm/api.rst +++ b/Documentation/virt/kvm/api.rst @@ -8022,7 +8022,7 @@ regardless of what has actually been exposed through the CPUID leaf. 8.29 KVM_CAP_DIRTY_LOG_RING
-: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 3bb134355874..7e04b0b8d2b2 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
For context, the documentation says:
<quote> - if KVM_CAP_DIRTY_LOG_RING is available, a number of pages at KVM_DIRTY_LOG_PAGE_OFFSET * PAGE_SIZE. [...] </quote>
What is the reason for picking this particular value?
#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..0309b2d0f2da 100644 --- a/arch/arm64/kvm/Kconfig +++ b/arch/arm64/kvm/Kconfig @@ -32,6 +32,7 @@ menuconfig KVM select KVM_VFIO select HAVE_KVM_EVENTFD select HAVE_KVM_IRQFD
- select HAVE_KVM_DIRTY_RING 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 986cee6fbc7f..3de6b9b39db7 100644 --- a/arch/arm64/kvm/arm.c +++ b/arch/arm64/kvm/arm.c @@ -866,6 +866,14 @@ int kvm_arch_vcpu_ioctl_run(struct kvm_vcpu *vcpu) if (!ret) ret = 1;
/* Force vcpu exit if its dirty ring is soft-full */if (unlikely(vcpu->kvm->dirty_ring_size &&kvm_dirty_ring_soft_full(&vcpu->dirty_ring))) {vcpu->run->exit_reason = KVM_EXIT_DIRTY_RING_FULL;trace_kvm_dirty_ring_exit(vcpu);ret = 0;}
Why can't this be moved to kvm_vcpu_exit_request() instead? I would also very much like the check to be made a common helper with x86.
A seemingly approach would be to make this a request on dirty log insertion, and avoid the whole "check the log size" on every run, which adds pointless overhead to unsuspecting users (aka everyone).
Thanks,
M.