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Message-Id: <20231125083400.1399197-2-pbonzini@redhat.com>
Date: Sat, 25 Nov 2023 03:33:57 -0500
From: Paolo Bonzini <pbonzini@...hat.com>
To: linux-kernel@...r.kernel.org, kvm@...r.kernel.org
Cc: seanjc@...gle.com, mlevitsk@...hat.com
Subject: [PATCH v2 1/4] KVM: x86/mmu: remove unnecessary "bool shared" argument from functions
Neither tdp_mmu_next_root nor kvm_tdp_mmu_put_root need to know
if the lock is taken for read or write. Either way, protection
is achieved via RCU and tdp_mmu_pages_lock. Remove the argument
and just assert that the lock is taken.
Reviewed-by: Maxim Levitsky <mlevitsk@...hat.com>
Signed-off-by: Paolo Bonzini <pbonzini@...hat.com>
---
arch/x86/kvm/mmu/mmu.c | 2 +-
arch/x86/kvm/mmu/tdp_mmu.c | 34 +++++++++++++++++++++-------------
arch/x86/kvm/mmu/tdp_mmu.h | 3 +--
3 files changed, 23 insertions(+), 16 deletions(-)
v1->v2: comment tweak
diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
index c57e181bba21..1cb81573a60b 100644
--- a/arch/x86/kvm/mmu/mmu.c
+++ b/arch/x86/kvm/mmu/mmu.c
@@ -3556,7 +3556,7 @@ static void mmu_free_root_page(struct kvm *kvm, hpa_t *root_hpa,
return;
if (is_tdp_mmu_page(sp))
- kvm_tdp_mmu_put_root(kvm, sp, false);
+ kvm_tdp_mmu_put_root(kvm, sp);
else if (!--sp->root_count && sp->role.invalid)
kvm_mmu_prepare_zap_page(kvm, sp, invalid_list);
diff --git a/arch/x86/kvm/mmu/tdp_mmu.c b/arch/x86/kvm/mmu/tdp_mmu.c
index 6cd4dd631a2f..05689c8d45b7 100644
--- a/arch/x86/kvm/mmu/tdp_mmu.c
+++ b/arch/x86/kvm/mmu/tdp_mmu.c
@@ -73,10 +73,13 @@ static void tdp_mmu_free_sp_rcu_callback(struct rcu_head *head)
tdp_mmu_free_sp(sp);
}
-void kvm_tdp_mmu_put_root(struct kvm *kvm, struct kvm_mmu_page *root,
- bool shared)
+void kvm_tdp_mmu_put_root(struct kvm *kvm, struct kvm_mmu_page *root)
{
- kvm_lockdep_assert_mmu_lock_held(kvm, shared);
+ /*
+ * Either read or write is okay, but mmu_lock must be held because
+ * writers are not required to take tdp_mmu_pages_lock.
+ */
+ lockdep_assert_held(&kvm->mmu_lock);
if (!refcount_dec_and_test(&root->tdp_mmu_root_count))
return;
@@ -106,10 +109,16 @@ void kvm_tdp_mmu_put_root(struct kvm *kvm, struct kvm_mmu_page *root,
*/
static struct kvm_mmu_page *tdp_mmu_next_root(struct kvm *kvm,
struct kvm_mmu_page *prev_root,
- bool shared, bool only_valid)
+ bool only_valid)
{
struct kvm_mmu_page *next_root;
+ /*
+ * While the roots themselves are RCU-protected, fields such as
+ * role.invalid are protected by mmu_lock.
+ */
+ lockdep_assert_held(&kvm->mmu_lock);
+
rcu_read_lock();
if (prev_root)
@@ -132,7 +141,7 @@ static struct kvm_mmu_page *tdp_mmu_next_root(struct kvm *kvm,
rcu_read_unlock();
if (prev_root)
- kvm_tdp_mmu_put_root(kvm, prev_root, shared);
+ kvm_tdp_mmu_put_root(kvm, prev_root);
return next_root;
}
@@ -144,13 +153,12 @@ static struct kvm_mmu_page *tdp_mmu_next_root(struct kvm *kvm,
* recent root. (Unless keeping a live reference is desirable.)
*
* If shared is set, this function is operating under the MMU lock in read
- * mode. In the unlikely event that this thread must free a root, the lock
- * will be temporarily dropped and reacquired in write mode.
+ * mode.
*/
#define __for_each_tdp_mmu_root_yield_safe(_kvm, _root, _as_id, _shared, _only_valid)\
- for (_root = tdp_mmu_next_root(_kvm, NULL, _shared, _only_valid); \
+ for (_root = tdp_mmu_next_root(_kvm, NULL, _only_valid); \
_root; \
- _root = tdp_mmu_next_root(_kvm, _root, _shared, _only_valid)) \
+ _root = tdp_mmu_next_root(_kvm, _root, _only_valid)) \
if (kvm_lockdep_assert_mmu_lock_held(_kvm, _shared) && \
kvm_mmu_page_as_id(_root) != _as_id) { \
} else
@@ -159,9 +167,9 @@ static struct kvm_mmu_page *tdp_mmu_next_root(struct kvm *kvm,
__for_each_tdp_mmu_root_yield_safe(_kvm, _root, _as_id, _shared, true)
#define for_each_tdp_mmu_root_yield_safe(_kvm, _root, _shared) \
- for (_root = tdp_mmu_next_root(_kvm, NULL, _shared, false); \
+ for (_root = tdp_mmu_next_root(_kvm, NULL, false); \
_root; \
- _root = tdp_mmu_next_root(_kvm, _root, _shared, false)) \
+ _root = tdp_mmu_next_root(_kvm, _root, false)) \
if (!kvm_lockdep_assert_mmu_lock_held(_kvm, _shared)) { \
} else
@@ -891,7 +899,7 @@ void kvm_tdp_mmu_zap_invalidated_roots(struct kvm *kvm)
* the root must be reachable by mmu_notifiers while it's being
* zapped
*/
- kvm_tdp_mmu_put_root(kvm, root, true);
+ kvm_tdp_mmu_put_root(kvm, root);
}
read_unlock(&kvm->mmu_lock);
@@ -1500,7 +1508,7 @@ void kvm_tdp_mmu_try_split_huge_pages(struct kvm *kvm,
for_each_valid_tdp_mmu_root_yield_safe(kvm, root, slot->as_id, shared) {
r = tdp_mmu_split_huge_pages_root(kvm, root, start, end, target_level, shared);
if (r) {
- kvm_tdp_mmu_put_root(kvm, root, shared);
+ kvm_tdp_mmu_put_root(kvm, root);
break;
}
}
diff --git a/arch/x86/kvm/mmu/tdp_mmu.h b/arch/x86/kvm/mmu/tdp_mmu.h
index 733a3aef3a96..20d97aa46c49 100644
--- a/arch/x86/kvm/mmu/tdp_mmu.h
+++ b/arch/x86/kvm/mmu/tdp_mmu.h
@@ -17,8 +17,7 @@ __must_check static inline bool kvm_tdp_mmu_get_root(struct kvm_mmu_page *root)
return refcount_inc_not_zero(&root->tdp_mmu_root_count);
}
-void kvm_tdp_mmu_put_root(struct kvm *kvm, struct kvm_mmu_page *root,
- bool shared);
+void kvm_tdp_mmu_put_root(struct kvm *kvm, struct kvm_mmu_page *root);
bool kvm_tdp_mmu_zap_leafs(struct kvm *kvm, gfn_t start, gfn_t end, bool flush);
bool kvm_tdp_mmu_zap_sp(struct kvm *kvm, struct kvm_mmu_page *sp);
--
2.39.1
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