[PATCH 10/12] KVM: cleanup and add shortcuts to kvm_range_has_memory_attributes()

Paolo Bonzini
2024-07-11T22:28:09Z

Use a guard to simplify early returns, and add two more easy
shortcuts. If the requested attributes are invalid, the attributes
xarray will never show them as set. And if testing a single page,
kvm_get_memory_attributes() is more efficient.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
---
virt/kvm/kvm_main.c | 42 ++++++++++++++++++++----------------------
1 file changed, 20 insertions(+), 22 deletions(-)

diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index f817ec66c85f..8ab9d8ff7b74 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -2392,6 +2392,14 @@ static int kvm_vm_ioctl_clear_dirty_log(struct kvm *kvm,
#endif /* CONFIG_KVM_GENERIC_DIRTYLOG_READ_PROTECT */

#ifdef CONFIG_KVM_GENERIC_MEMORY_ATTRIBUTES
+static u64 kvm_supported_mem_attributes(struct kvm *kvm)
+{
+ if (!kvm || kvm_arch_has_private_mem(kvm))
+ return KVM_MEMORY_ATTRIBUTE_PRIVATE;
+
+ return 0;
+}
+
/*
* Returns true if _all_ gfns in the range [@start, @end) have attributes
* matching @attrs.
@@ -2400,40 +2408,30 @@ bool kvm_range_has_memory_attributes(struct kvm *kvm, gfn_t start, gfn_t end,
unsigned long attrs)
{
XA_STATE(xas, &kvm->mem_attr_array, start);
+ unsigned long mask = kvm_supported_mem_attributes(kvm);;
unsigned long index;
- bool has_attrs;
void *entry;

- rcu_read_lock();
+ if (attrs & ~mask)
+ return false;

- if (!attrs) {
- has_attrs = !xas_find(&xas, end - 1);
- goto out;
- }
+ if (end == start + 1)
+ return kvm_get_memory_attributes(kvm, start) == attrs;
+
+ guard(rcu)();
+ if (!attrs)
+ return !xas_find(&xas, end - 1);

- has_attrs = true;
for (index = start; index < end; index++) {
do {
entry = xas_next(&xas);
} while (xas_retry(&xas, entry));

- if (xas.xa_index != index || xa_to_value(entry) != attrs) {
- has_attrs = false;
- break;
- }
+ if (xas.xa_index != index || xa_to_value(entry) != attrs)
+ return false;
}

-out:
- rcu_read_unlock();
- return has_attrs;
-}
-
-static u64 kvm_supported_mem_attributes(struct kvm *kvm)
-{
- if (!kvm || kvm_arch_has_private_mem(kvm))
- return KVM_MEMORY_ATTRIBUTE_PRIVATE;
-
- return 0;
+ return true;
}

static __always_inline void kvm_handle_gfn_range(struct kvm *kvm,
--
2.43.0