Introduce kvm_arch_dirty_ring_clear() that allow implementation of
arch-specific hardware-accelerated dirty-ring routines.

A call to that is added on kvm_dirty_ring_reset() and will fall back to
software version if not implemented, or any error was detected in the
arch-specific routine.

For an arch to implement this function, it's required to provide it in a
asm/kvm_dirty_bit.h and have CONFIG_HAVE_KVM_HW_DIRTY_BIT=y on building.

If the arch does not implement it, and thus lack above config, the
introduced snippet is expected to be compiled-out and have zero impact at
runtime.

Signed-off-by: Leonardo Bras <leo.bras@arm.com>
---
 include/linux/kvm_dirty_bit.h | 7 +++++++
 virt/kvm/dirty_ring.c         | 4 ++++
 2 files changed, 11 insertions(+)

diff --git a/include/linux/kvm_dirty_bit.h b/include/linux/kvm_dirty_bit.h
index fa4f6b67b623..8492979d694e 100644
--- a/include/linux/kvm_dirty_bit.h
+++ b/include/linux/kvm_dirty_bit.h
@@ -11,17 +11,24 @@
 
 static inline int kvm_arch_dirty_log_clear(struct kvm *kvm,
 					   struct kvm_memory_slot *memslot,
 					   struct kvm_clear_dirty_log *log,
 					   unsigned long *bitmap,
 					   bool *flush)
 {
 	return -ENXIO;
 }
 
+static inline int kvm_arch_dirty_ring_clear(struct kvm *kvm,
+					    struct kvm_dirty_ring *ring,
+					    int *nr_entries_reset)
+{
+	return -ENXIO;
+}
+
 #else /* CONFIG_HAVE_KVM_HW_DIRTY_BIT */
 
 #include <asm/kvm_dirty_bit.h>
 
 #endif /* CONFIG_HAVE_KVM_HW_DIRTY_BIT */
 
 #endif /* __KVM_DIRTY_BIT_H__ */
diff --git a/virt/kvm/dirty_ring.c b/virt/kvm/dirty_ring.c
index 83ac5ac907c1..a58c811dd461 100644
--- a/virt/kvm/dirty_ring.c
+++ b/virt/kvm/dirty_ring.c
@@ -1,20 +1,21 @@
 // SPDX-License-Identifier: GPL-2.0-only
 /*
  * KVM dirty ring implementation
  *
  * Copyright 2019 Red Hat, Inc.
  */
 #include <linux/kvm_host.h>
 #include <linux/kvm.h>
 #include <linux/vmalloc.h>
 #include <linux/kvm_dirty_ring.h>
+#include <linux/kvm_dirty_bit.h>
 #include <trace/events/kvm.h>
 #include "kvm_mm.h"
 
 int __weak kvm_cpu_dirty_log_size(struct kvm *kvm)
 {
 	return 0;
 }
 
 u32 kvm_dirty_ring_get_rsvd_entries(struct kvm *kvm)
 {
@@ -125,20 +126,23 @@ int kvm_dirty_ring_reset(struct kvm *kvm, struct kvm_dirty_ring *ring,
 	struct kvm_dirty_gfn *entry;
 
 	/*
 	 * Ensure concurrent calls to KVM_RESET_DIRTY_RINGS are serialized,
 	 * e.g. so that KVM fully resets all entries processed by a given call
 	 * before returning to userspace.  Holding slots_lock also protects
 	 * the various memslot accesses.
 	 */
 	lockdep_assert_held(&kvm->slots_lock);
 
+	if (kvm_arch_dirty_ring_clear(kvm, ring, nr_entries_reset) >= 0)
+		return 0;
+
 	while (likely((*nr_entries_reset) < INT_MAX)) {
 		if (signal_pending(current))
 			return -EINTR;
 
 		entry = &ring->dirty_gfns[ring->reset_index & (ring->size - 1)];
 
 		if (!kvm_dirty_gfn_harvested(entry))
 			break;
 
 		next_slot = READ_ONCE(entry->slot);
-- 
2.54.0