Re: [PATCH v3 3/6] KVM: arm64: Enable ring-based dirty memory tracking

[Marc Zyngier <maz@kernel.org>]

On Thu, 22 Sep 2022 01:32:11 +0100,
Gavin Shan <gshan@redhat.com> wrote:
> 
> This enables the ring-based dirty memory tracking on ARM64. The
> feature is configured by CONFIG_HAVE_KVM_DIRTY_RING, detected and
> enabled by KVM_CAP_DIRTY_LOG_RING. A ring buffer is created on every
> VCPU when the feature is enabled. Each entry in the ring buffer is
> described by 'struct kvm_dirty_gfn'.
> 
> A ring buffer entry is pushed when a page becomes dirty on host,
> and pulled by userspace after the ring buffer is mapped at physical
> page offset KVM_DIRTY_LOG_PAGE_OFFSET. The specific VCPU is enforced
> to exit if its ring buffer becomes softly full. Besides, the ring
> buffer can be reset by ioctl command KVM_RESET_DIRTY_RINGS to release
> those pulled ring buffer entries.

I think you can cut this message short. This description was useful
when the feature was initially merged, but this is only a "plumb the
damn thing" patch.

> 
> 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 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..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 2ff0ef62abad..76816f8e082b 100644
> --- a/arch/arm64/kvm/arm.c
> +++ b/arch/arm64/kvm/arm.c
> @@ -747,6 +747,14 @@ static int check_vcpu_requests(struct kvm_vcpu *vcpu)
>  
>  		if (kvm_check_request(KVM_REQ_SUSPEND, vcpu))
>  			return kvm_vcpu_suspend(vcpu);
> +
> +		if (kvm_check_request(KVM_REQ_RING_SOFT_FULL, vcpu) &&
> +		    kvm_dirty_ring_soft_full(&vcpu->dirty_ring)) {
> +			kvm_make_request(KVM_REQ_RING_SOFT_FULL, vcpu);
> +			vcpu->run->exit_reason = KVM_EXIT_DIRTY_RING_FULL;
> +			trace_kvm_dirty_ring_exit(vcpu);
> +			return 0;
> +		}

This is *very* similar to the x86 code. Could we move it to common
code? Something like the diff below, to be for most of it squashed
into patch #1.

Thanks,

	M.

diff --git a/arch/arm64/kvm/arm.c b/arch/arm64/kvm/arm.c
index 76816f8e082b..93a16cdbe163 100644
--- a/arch/arm64/kvm/arm.c
+++ b/arch/arm64/kvm/arm.c
@@ -748,13 +748,8 @@ static int check_vcpu_requests(struct kvm_vcpu *vcpu)
 		if (kvm_check_request(KVM_REQ_SUSPEND, vcpu))
 			return kvm_vcpu_suspend(vcpu);
 
-		if (kvm_check_request(KVM_REQ_RING_SOFT_FULL, vcpu) &&
-		    kvm_dirty_ring_soft_full(&vcpu->dirty_ring)) {
-			kvm_make_request(KVM_REQ_RING_SOFT_FULL, vcpu);
-			vcpu->run->exit_reason = KVM_EXIT_DIRTY_RING_FULL;
-			trace_kvm_dirty_ring_exit(vcpu);
+		if (kvm_dirty_ring_check_request(vcpu))
 			return 0;
-		}
 	}
 
 	return 1;
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index eb7d0d7654bb..48f2519b1db7 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -10249,11 +10249,7 @@ static int vcpu_enter_guest(struct kvm_vcpu *vcpu)
 
 	if (kvm_request_pending(vcpu)) {
 		/* Forbid vmenter if vcpu dirty ring is soft-full */
-		if (kvm_check_request(KVM_REQ_RING_SOFT_FULL, vcpu) &&
-		    kvm_dirty_ring_soft_full(&vcpu->dirty_ring)) {
-			kvm_make_request(KVM_REQ_RING_SOFT_FULL, vcpu);
-			vcpu->run->exit_reason = KVM_EXIT_DIRTY_RING_FULL;
-			trace_kvm_dirty_ring_exit(vcpu);
+		if (kvm_dirty_ring_check_request(vcpu)) {
 			r = 0;
 			goto out;
 		}
diff --git a/include/linux/kvm_dirty_ring.h b/include/linux/kvm_dirty_ring.h
index 8c6755981c9b..6e484220adc0 100644
--- a/include/linux/kvm_dirty_ring.h
+++ b/include/linux/kvm_dirty_ring.h
@@ -64,11 +64,6 @@ static inline void kvm_dirty_ring_free(struct kvm_dirty_ring *ring)
 {
 }
 
-static inline bool kvm_dirty_ring_soft_full(struct kvm_dirty_ring *ring)
-{
-	return true;
-}
-
 #else /* CONFIG_HAVE_KVM_DIRTY_RING */
 
 int kvm_cpu_dirty_log_size(void);
@@ -91,7 +86,7 @@ void kvm_dirty_ring_push(struct kvm_dirty_ring *ring, u32 slot, u64 offset);
 struct page *kvm_dirty_ring_get_page(struct kvm_dirty_ring *ring, u32 offset);
 
 void kvm_dirty_ring_free(struct kvm_dirty_ring *ring);
-bool kvm_dirty_ring_soft_full(struct kvm_dirty_ring *ring);
+bool kvm_dirty_ring_check_request(struct kvm_vcpu *vcpu);
 
 #endif /* CONFIG_HAVE_KVM_DIRTY_RING */
 
diff --git a/virt/kvm/dirty_ring.c b/virt/kvm/dirty_ring.c
index 69c8c90d489d..436d7cded5bf 100644
--- a/virt/kvm/dirty_ring.c
+++ b/virt/kvm/dirty_ring.c
@@ -26,7 +26,7 @@ static u32 kvm_dirty_ring_used(struct kvm_dirty_ring *ring)
 	return READ_ONCE(ring->dirty_index) - READ_ONCE(ring->reset_index);
 }
 
-bool kvm_dirty_ring_soft_full(struct kvm_dirty_ring *ring)
+static bool kvm_dirty_ring_soft_full(struct kvm_dirty_ring *ring)
 {
 	return kvm_dirty_ring_used(ring) >= ring->soft_limit;
 }
@@ -182,3 +182,16 @@ void kvm_dirty_ring_free(struct kvm_dirty_ring *ring)
 	vfree(ring->dirty_gfns);
 	ring->dirty_gfns = NULL;
 }
+
+bool kvm_dirty_ring_check_request(struct kvm_vcpu *vcpu)
+{
+	if (kvm_check_request(KVM_REQ_RING_SOFT_FULL, vcpu) &&
+	    kvm_dirty_ring_soft_full(&vcpu->dirty_ring)) {
+		kvm_make_request(KVM_REQ_RING_SOFT_FULL, vcpu);
+		vcpu->run->exit_reason = KVM_EXIT_DIRTY_RING_FULL;
+		trace_kvm_dirty_ring_exit(vcpu);
+		return true;
+	}
+
+	return false;
+}

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