Commit c0e64238 authored by Ben Gardon's avatar Ben Gardon Committed by Paolo Bonzini
Browse files

KVM: x86/mmu: Protect the tdp_mmu_roots list with RCU



Protect the contents of the TDP MMU roots list with RCU in preparation
for a future patch which will allow the iterator macro to be used under
the MMU lock in read mode.

Signed-off-by: default avatarBen Gardon <bgardon@google.com>
Message-Id: <20210401233736.638171-9-bgardon@google.com>
Signed-off-by: default avatarPaolo Bonzini <pbonzini@redhat.com>
parent fb101293
......@@ -1059,25 +1059,36 @@ struct kvm_arch {
bool tdp_mmu_enabled;
/*
* List of struct kvmp_mmu_pages being used as roots.
* List of struct kvm_mmu_pages being used as roots.
* All struct kvm_mmu_pages in the list should have
* tdp_mmu_page set.
* All struct kvm_mmu_pages in the list should have a positive
* root_count except when a thread holds the MMU lock and is removing
* an entry from the list.
*
* For reads, this list is protected by:
* the MMU lock in read mode + RCU or
* the MMU lock in write mode
*
* For writes, this list is protected by:
* the MMU lock in read mode + the tdp_mmu_pages_lock or
* the MMU lock in write mode
*
* Roots will remain in the list until their tdp_mmu_root_count
* drops to zero, at which point the thread that decremented the
* count to zero should removed the root from the list and clean
* it up, freeing the root after an RCU grace period.
*/
struct list_head tdp_mmu_roots;
/*
* List of struct kvmp_mmu_pages not being used as roots.
* All struct kvm_mmu_pages in the list should have
* tdp_mmu_page set and a root_count of 0.
* tdp_mmu_page set and a tdp_mmu_root_count of 0.
*/
struct list_head tdp_mmu_pages;
/*
* Protects accesses to the following fields when the MMU lock
* is held in read mode:
* - tdp_mmu_roots (above)
* - tdp_mmu_pages (above)
* - the link field of struct kvm_mmu_pages used by the TDP MMU
* - lpage_disallowed_mmu_pages
......
......@@ -50,6 +50,22 @@ static void tdp_mmu_free_sp(struct kvm_mmu_page *sp)
kmem_cache_free(mmu_page_header_cache, sp);
}
/*
* This is called through call_rcu in order to free TDP page table memory
* safely with respect to other kernel threads that may be operating on
* the memory.
* By only accessing TDP MMU page table memory in an RCU read critical
* section, and freeing it after a grace period, lockless access to that
* memory won't use it after it is freed.
*/
static void tdp_mmu_free_sp_rcu_callback(struct rcu_head *head)
{
struct kvm_mmu_page *sp = container_of(head, struct kvm_mmu_page,
rcu_head);
tdp_mmu_free_sp(sp);
}
void kvm_tdp_mmu_put_root(struct kvm *kvm, struct kvm_mmu_page *root)
{
gfn_t max_gfn = 1ULL << (shadow_phys_bits - PAGE_SHIFT);
......@@ -61,11 +77,13 @@ void kvm_tdp_mmu_put_root(struct kvm *kvm, struct kvm_mmu_page *root)
WARN_ON(!root->tdp_mmu_page);
list_del(&root->link);
spin_lock(&kvm->arch.tdp_mmu_pages_lock);
list_del_rcu(&root->link);
spin_unlock(&kvm->arch.tdp_mmu_pages_lock);
zap_gfn_range(kvm, root, 0, max_gfn, false, false);
tdp_mmu_free_sp(root);
call_rcu(&root->rcu_head, tdp_mmu_free_sp_rcu_callback);
}
/*
......@@ -82,18 +100,21 @@ static struct kvm_mmu_page *tdp_mmu_next_root(struct kvm *kvm,
lockdep_assert_held_write(&kvm->mmu_lock);
rcu_read_lock();
if (prev_root)
next_root = list_next_entry(prev_root, link);
next_root = list_next_or_null_rcu(&kvm->arch.tdp_mmu_roots,
&prev_root->link,
typeof(*prev_root), link);
else
next_root = list_first_entry(&kvm->arch.tdp_mmu_roots,
typeof(*next_root), link);
next_root = list_first_or_null_rcu(&kvm->arch.tdp_mmu_roots,
typeof(*next_root), link);
while (!list_entry_is_head(next_root, &kvm->arch.tdp_mmu_roots, link) &&
!kvm_tdp_mmu_get_root(kvm, next_root))
next_root = list_next_entry(next_root, link);
while (next_root && !kvm_tdp_mmu_get_root(kvm, next_root))
next_root = list_next_or_null_rcu(&kvm->arch.tdp_mmu_roots,
&next_root->link, typeof(*next_root), link);
if (list_entry_is_head(next_root, &kvm->arch.tdp_mmu_roots, link))
next_root = NULL;
rcu_read_unlock();
if (prev_root)
kvm_tdp_mmu_put_root(kvm, prev_root);
......@@ -107,15 +128,17 @@ static struct kvm_mmu_page *tdp_mmu_next_root(struct kvm *kvm,
* if exiting the loop early, the caller must drop the reference to the most
* recent root. (Unless keeping a live reference is desirable.)
*/
#define for_each_tdp_mmu_root_yield_safe(_kvm, _root, _as_id) \
#define for_each_tdp_mmu_root_yield_safe(_kvm, _root, _as_id) \
for (_root = tdp_mmu_next_root(_kvm, NULL); \
_root; \
_root = tdp_mmu_next_root(_kvm, _root)) \
if (kvm_mmu_page_as_id(_root) != _as_id) { \
} else
#define for_each_tdp_mmu_root(_kvm, _root, _as_id) \
list_for_each_entry(_root, &_kvm->arch.tdp_mmu_roots, link) \
#define for_each_tdp_mmu_root(_kvm, _root, _as_id) \
list_for_each_entry_rcu(_root, &_kvm->arch.tdp_mmu_roots, link, \
lockdep_is_held_type(&kvm->mmu_lock, 0) || \
lockdep_is_held(&kvm->arch.tdp_mmu_pages_lock)) \
if (kvm_mmu_page_as_id(_root) != _as_id) { \
} else
......@@ -171,28 +194,14 @@ hpa_t kvm_tdp_mmu_get_vcpu_root_hpa(struct kvm_vcpu *vcpu)
root = alloc_tdp_mmu_page(vcpu, 0, vcpu->arch.mmu->shadow_root_level);
refcount_set(&root->tdp_mmu_root_count, 1);
list_add(&root->link, &kvm->arch.tdp_mmu_roots);
spin_lock(&kvm->arch.tdp_mmu_pages_lock);
list_add_rcu(&root->link, &kvm->arch.tdp_mmu_roots);
spin_unlock(&kvm->arch.tdp_mmu_pages_lock);
out:
return __pa(root->spt);
}
/*
* This is called through call_rcu in order to free TDP page table memory
* safely with respect to other kernel threads that may be operating on
* the memory.
* By only accessing TDP MMU page table memory in an RCU read critical
* section, and freeing it after a grace period, lockless access to that
* memory won't use it after it is freed.
*/
static void tdp_mmu_free_sp_rcu_callback(struct rcu_head *head)
{
struct kvm_mmu_page *sp = container_of(head, struct kvm_mmu_page,
rcu_head);
tdp_mmu_free_sp(sp);
}
static void handle_changed_spte(struct kvm *kvm, int as_id, gfn_t gfn,
u64 old_spte, u64 new_spte, int level,
bool shared);
......
Supports Markdown
0% or .
You are about to add 0 people to the discussion. Proceed with caution.
Finish editing this message first!
Please register or to comment