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Message-Id: <20240822065544.65013-1-zhangpeng.00@bytedance.com>
Date: Thu, 22 Aug 2024 14:55:44 +0800
From: Peng Zhang <zhangpeng.00@...edance.com>
To: pbonzini@...hat.com,
chao.p.peng@...ux.intel.com,
seanjc@...gle.com,
Liam.Howlett@...cle.com
Cc: kvm@...r.kernel.org,
linux-kernel@...r.kernel.org,
maple-tree@...ts.infradead.org,
Peng Zhang <zhangpeng.00@...edance.com>
Subject: [PATCH RFC] KVM: Use maple tree to manage memory attributes.
Currently, xarray is used to manage memory attributes. The memory
attributes management here is an interval problem. However, xarray is
not suitable for handling interval problems. It may cause memory waste
and is not efficient. Switching it to maple tree is more elegant. Using
maple tree here has the following three advantages:
1. Less memory overhead.
2. More efficient interval operations.
3. Simpler code.
This is the first user of the maple tree interface mas_find_range(),
and it does not have any test cases yet, so its stability is unclear.
Signed-off-by: Peng Zhang <zhangpeng.00@...edance.com>
---
include/linux/kvm_host.h | 5 +++--
virt/kvm/kvm_main.c | 47 ++++++++++++++--------------------------
2 files changed, 19 insertions(+), 33 deletions(-)
I haven't tested this code yet, and I'm not very familiar with kvm, so I'd
be happy if someone could help test it. This is just an RFC now. Any comments
are welcome.
diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
index 79a6b1a63027..9b3351d88d64 100644
--- a/include/linux/kvm_host.h
+++ b/include/linux/kvm_host.h
@@ -35,6 +35,7 @@
#include <linux/interval_tree.h>
#include <linux/rbtree.h>
#include <linux/xarray.h>
+#include <linux/maple_tree.h>
#include <asm/signal.h>
#include <linux/kvm.h>
@@ -839,7 +840,7 @@ struct kvm {
#endif
#ifdef CONFIG_KVM_GENERIC_MEMORY_ATTRIBUTES
/* Protected by slots_locks (for writes) and RCU (for reads) */
- struct xarray mem_attr_array;
+ struct maple_tree mem_attr_mtree;
#endif
char stats_id[KVM_STATS_NAME_SIZE];
};
@@ -2410,7 +2411,7 @@ static inline void kvm_prepare_memory_fault_exit(struct kvm_vcpu *vcpu,
#ifdef CONFIG_KVM_GENERIC_MEMORY_ATTRIBUTES
static inline unsigned long kvm_get_memory_attributes(struct kvm *kvm, gfn_t gfn)
{
- return xa_to_value(xa_load(&kvm->mem_attr_array, gfn));
+ return xa_to_value(mtree_load(&kvm->mem_attr_mtree, gfn));
}
bool kvm_range_has_memory_attributes(struct kvm *kvm, gfn_t start, gfn_t end,
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index 92901656a0d4..9a99c334f4af 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -10,6 +10,7 @@
* Yaniv Kamay <yaniv@...ranet.com>
*/
+#include "linux/maple_tree.h"
#include <kvm/iodev.h>
#include <linux/kvm_host.h>
@@ -1159,7 +1160,8 @@ static struct kvm *kvm_create_vm(unsigned long type, const char *fdname)
rcuwait_init(&kvm->mn_memslots_update_rcuwait);
xa_init(&kvm->vcpu_array);
#ifdef CONFIG_KVM_GENERIC_MEMORY_ATTRIBUTES
- xa_init(&kvm->mem_attr_array);
+ mt_init_flags(&kvm->mem_attr_mtree, MT_FLAGS_LOCK_EXTERN);
+ mt_set_external_lock(&kvm->mem_attr_mtree, &kvm->slots_lock);
#endif
INIT_LIST_HEAD(&kvm->gpc_list);
@@ -1356,7 +1358,9 @@ static void kvm_destroy_vm(struct kvm *kvm)
cleanup_srcu_struct(&kvm->irq_srcu);
cleanup_srcu_struct(&kvm->srcu);
#ifdef CONFIG_KVM_GENERIC_MEMORY_ATTRIBUTES
- xa_destroy(&kvm->mem_attr_array);
+ mutex_lock(&kvm->slots_lock);
+ __mt_destroy(&kvm->mem_attr_mtree);
+ mutex_unlock(&kvm->slots_lock);
#endif
kvm_arch_free_vm(kvm);
preempt_notifier_dec();
@@ -2413,30 +2417,20 @@ static u64 kvm_supported_mem_attributes(struct kvm *kvm)
bool kvm_range_has_memory_attributes(struct kvm *kvm, gfn_t start, gfn_t end,
unsigned long mask, unsigned long attrs)
{
- XA_STATE(xas, &kvm->mem_attr_array, start);
- unsigned long index;
+ MA_STATE(mas, &kvm->mem_attr_mtree, start, start);
void *entry;
mask &= kvm_supported_mem_attributes(kvm);
if (attrs & ~mask)
return false;
- if (end == start + 1)
- return (kvm_get_memory_attributes(kvm, start) & mask) == attrs;
-
guard(rcu)();
- if (!attrs)
- return !xas_find(&xas, end - 1);
-
- 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) & mask) != attrs)
+ do {
+ entry = mas_find_range(&mas, end - 1);
+ if ((xa_to_value(entry) & mask) != attrs)
return false;
- }
+ } while (mas.last < end - 1);
return true;
}
@@ -2524,9 +2518,9 @@ static int kvm_vm_set_mem_attributes(struct kvm *kvm, gfn_t start, gfn_t end,
.on_lock = kvm_mmu_invalidate_end,
.may_block = true,
};
- unsigned long i;
void *entry;
int r = 0;
+ MA_STATE(mas, &kvm->mem_attr_mtree, start, end - 1);
entry = attributes ? xa_mk_value(attributes) : NULL;
@@ -2540,20 +2534,11 @@ static int kvm_vm_set_mem_attributes(struct kvm *kvm, gfn_t start, gfn_t end,
* Reserve memory ahead of time to avoid having to deal with failures
* partway through setting the new attributes.
*/
- for (i = start; i < end; i++) {
- r = xa_reserve(&kvm->mem_attr_array, i, GFP_KERNEL_ACCOUNT);
- if (r)
- goto out_unlock;
- }
-
+ r = mas_preallocate(&mas, entry, GFP_KERNEL_ACCOUNT);
+ if (r)
+ goto out_unlock;
kvm_handle_gfn_range(kvm, &pre_set_range);
-
- for (i = start; i < end; i++) {
- r = xa_err(xa_store(&kvm->mem_attr_array, i, entry,
- GFP_KERNEL_ACCOUNT));
- KVM_BUG_ON(r, kvm);
- }
-
+ mas_store_prealloc(&mas, entry);
kvm_handle_gfn_range(kvm, &post_set_range);
out_unlock:
--
2.20.1
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