linux-kernel - [PATCH 12/29] KVM: share dirty ring for same vCPU id on different planes

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Message-ID: <20250401161106.790710-13-pbonzini@redhat.com>
Date: Tue,  1 Apr 2025 18:10:49 +0200
From: Paolo Bonzini <pbonzini@...hat.com>
To: linux-kernel@...r.kernel.org,
	kvm@...r.kernel.org
Cc: roy.hopkins@...e.com,
	seanjc@...gle.com,
	thomas.lendacky@....com,
	ashish.kalra@....com,
	michael.roth@....com,
	jroedel@...e.de,
	nsaenz@...zon.com,
	anelkz@...zon.de,
	James.Bottomley@...senPartnership.com
Subject: [PATCH 12/29] KVM: share dirty ring for same vCPU id on different planes

The dirty page ring is read by mmap()-ing the vCPU file descriptor,
which is only possible for plane 0.  This is not a problem because it
is only filled by KVM_RUN which takes the plane-0 vCPU mutex, and it is
therefore possible to share it for vCPUs that have the same id but are
on different planes.  (TODO: double check).

Signed-off-by: Paolo Bonzini <pbonzini@...hat.com>
---
 include/linux/kvm_host.h |  6 ++++--
 virt/kvm/dirty_ring.c    |  5 +++--
 virt/kvm/kvm_main.c      | 10 +++++-----
 3 files changed, 12 insertions(+), 9 deletions(-)

diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
index d2e0c0e8ff17..b511aed2de8e 100644
--- a/include/linux/kvm_host.h
+++ b/include/linux/kvm_host.h
@@ -394,9 +394,11 @@ struct kvm_vcpu {
 	bool scheduled_out;
 	struct kvm_vcpu_arch arch;
 	struct kvm_vcpu_stat *stat;
-	struct kvm_vcpu_stat __stat;
 	char stats_id[KVM_STATS_NAME_SIZE];
-	struct kvm_dirty_ring dirty_ring;
+	struct kvm_dirty_ring *dirty_ring;
+
+	struct kvm_vcpu_stat __stat;
+	struct kvm_dirty_ring __dirty_ring;
 
 	/*
 	 * The most recently used memslot by this vCPU and the slots generation
diff --git a/virt/kvm/dirty_ring.c b/virt/kvm/dirty_ring.c
index d14ffc7513ee..66e6a6a67d13 100644
--- a/virt/kvm/dirty_ring.c
+++ b/virt/kvm/dirty_ring.c
@@ -172,11 +172,12 @@ int kvm_dirty_ring_reset(struct kvm *kvm, struct kvm_dirty_ring *ring)
 
 void kvm_dirty_ring_push(struct kvm_vcpu *vcpu, u32 slot, u64 offset)
 {
-	struct kvm_dirty_ring *ring = &vcpu->dirty_ring;
+	struct kvm_dirty_ring *ring = vcpu->dirty_ring;
 	struct kvm_dirty_gfn *entry;
 
 	/* It should never get full */
 	WARN_ON_ONCE(kvm_dirty_ring_full(ring));
+	lockdep_assert_held(&vcpu->plane0->mutex);
 
 	entry = &ring->dirty_gfns[ring->dirty_index & (ring->size - 1)];
 
@@ -204,7 +205,7 @@ bool kvm_dirty_ring_check_request(struct kvm_vcpu *vcpu)
 	 * the dirty ring is reset by userspace.
 	 */
 	if (kvm_check_request(KVM_REQ_DIRTY_RING_SOFT_FULL, vcpu) &&
-	    kvm_dirty_ring_soft_full(&vcpu->dirty_ring)) {
+	    kvm_dirty_ring_soft_full(vcpu->dirty_ring)) {
 		kvm_make_request(KVM_REQ_DIRTY_RING_SOFT_FULL, vcpu);
 		vcpu->run->exit_reason = KVM_EXIT_DIRTY_RING_FULL;
 		trace_kvm_dirty_ring_exit(vcpu);
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index 4c7e379fbf7d..863fd80ddfbe 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -466,7 +466,7 @@ static void kvm_vcpu_init(struct kvm_vcpu *vcpu, struct kvm *kvm, unsigned id)
 static void kvm_vcpu_destroy(struct kvm_vcpu *vcpu)
 {
 	kvm_arch_vcpu_destroy(vcpu);
-	kvm_dirty_ring_free(&vcpu->dirty_ring);
+	kvm_dirty_ring_free(vcpu->dirty_ring);
 
 	/*
 	 * No need for rcu_read_lock as VCPU_RUN is the only place that changes
@@ -4038,7 +4038,7 @@ static vm_fault_t kvm_vcpu_fault(struct vm_fault *vmf)
 #endif
 	else if (kvm_page_in_dirty_ring(vcpu->kvm, vmf->pgoff))
 		page = kvm_dirty_ring_get_page(
-		    &vcpu->dirty_ring,
+		    vcpu->dirty_ring,
 		    vmf->pgoff - KVM_DIRTY_LOG_PAGE_OFFSET);
 	else
 		return kvm_arch_vcpu_fault(vcpu, vmf);
@@ -4174,7 +4174,7 @@ static int kvm_vm_ioctl_create_vcpu(struct kvm *kvm, unsigned long id)
 	vcpu->run = page_address(page);
 
 	if (kvm->dirty_ring_size) {
-		r = kvm_dirty_ring_alloc(kvm, &vcpu->dirty_ring,
+		r = kvm_dirty_ring_alloc(kvm, &vcpu->__dirty_ring,
 					 id, kvm->dirty_ring_size);
 		if (r)
 			goto vcpu_free_run_page;
@@ -4242,7 +4242,7 @@ static int kvm_vm_ioctl_create_vcpu(struct kvm *kvm, unsigned long id)
 	mutex_unlock(&kvm->lock);
 	kvm_arch_vcpu_destroy(vcpu);
 vcpu_free_dirty_ring:
-	kvm_dirty_ring_free(&vcpu->dirty_ring);
+	kvm_dirty_ring_free(&vcpu->__dirty_ring);
 vcpu_free_run_page:
 	free_page((unsigned long)vcpu->run);
 vcpu_free:
@@ -5047,7 +5047,7 @@ static int kvm_vm_ioctl_reset_dirty_pages(struct kvm *kvm)
 	mutex_lock(&kvm->slots_lock);
 
 	kvm_for_each_vcpu(i, vcpu, kvm)
-		cleared += kvm_dirty_ring_reset(vcpu->kvm, &vcpu->dirty_ring);
+		cleared += kvm_dirty_ring_reset(vcpu->kvm, vcpu->dirty_ring);
 
 	mutex_unlock(&kvm->slots_lock);
 
-- 
2.49.0