[PATCH v3 1/2] KVM: x86/mmu: Track TDP MMU NX huge pages separately

Vipin Sharma
2024-09-06T20:45:20Z

Create separate list for storing TDP MMU NX huge pages and provide
counter for it. Use this list in NX huge page recovery worker along with
the existing NX huge pages list. Use old NX huge pages list for storing
only non-TDP MMU pages and provide separate counter for it.

Separate list will allow to optimize TDP MMU NX huge page recovery in
future patches by using MMU read lock.

Suggested-by: Sean Christopherson <seanjc@google.com>
Suggested-by: David Matlack <dmatlack@google.com>
Signed-off-by: Vipin Sharma <vipinsh@google.com>
---
arch/x86/include/asm/kvm_host.h | 13 ++++++++++-
arch/x86/kvm/mmu/mmu.c | 39 +++++++++++++++++++++++----------
arch/x86/kvm/mmu/mmu_internal.h | 8 +++++--
arch/x86/kvm/mmu/tdp_mmu.c | 19 ++++++++++++----
arch/x86/kvm/mmu/tdp_mmu.h | 1 +
5 files changed, 61 insertions(+), 19 deletions(-)

diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index 950a03e0181e..0f21f9a69285 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -1318,8 +1318,12 @@ struct kvm_arch {
* guarantee an NX huge page will be created in its stead, e.g. if the
* guest attempts to execute from the region then KVM obviously can't
* create an NX huge page (without hanging the guest).
+ *
+ * This list only contains shadow and legacy MMU pages. TDP MMU pages
+ * are stored separately in tdp_mmu_possible_nx_huge_pages.
*/
struct list_head possible_nx_huge_pages;
+ u64 nr_possible_nx_huge_pages;
#ifdef CONFIG_KVM_EXTERNAL_WRITE_TRACKING
struct kvm_page_track_notifier_head track_notifier_head;
#endif
@@ -1474,7 +1478,7 @@ struct kvm_arch {
* is held in read mode:
* - tdp_mmu_roots (above)
* - the link field of kvm_mmu_page structs used by the TDP MMU
- * - possible_nx_huge_pages;
+ * - tdp_mmu_possible_nx_huge_pages
* - the possible_nx_huge_page_link field of kvm_mmu_page structs used
* by the TDP MMU
* Because the lock is only taken within the MMU lock, strictly
@@ -1483,6 +1487,13 @@ struct kvm_arch {
* the code to do so.
*/
spinlock_t tdp_mmu_pages_lock;
+
+ /*
+ * Similar to possible_nx_huge_pages list but this one stores only TDP
+ * MMU pages.
+ */
+ struct list_head tdp_mmu_possible_nx_huge_pages;
+ u64 tdp_mmu_nr_possible_nx_huge_pages;
#endif /* CONFIG_X86_64 */

/*
diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
index 901be9e420a4..455caaaa04f5 100644
--- a/arch/x86/kvm/mmu/mmu.c
+++ b/arch/x86/kvm/mmu/mmu.c
@@ -857,7 +857,8 @@ static void account_shadowed(struct kvm *kvm, struct kvm_mmu_page *sp)
kvm_flush_remote_tlbs_gfn(kvm, gfn, PG_LEVEL_4K);
}

-void track_possible_nx_huge_page(struct kvm *kvm, struct kvm_mmu_page *sp)
+void track_possible_nx_huge_page(struct kvm *kvm, struct kvm_mmu_page *sp,
+ struct list_head *pages, u64 *nr_pages)
{
/*
* If it's possible to replace the shadow page with an NX huge page,
@@ -870,9 +871,9 @@ void track_possible_nx_huge_page(struct kvm *kvm, struct kvm_mmu_page *sp)
if (!list_empty(&sp->possible_nx_huge_page_link))
return;

+ ++(*nr_pages);
++kvm->stat.nx_lpage_splits;
- list_add_tail(&sp->possible_nx_huge_page_link,
- &kvm->arch.possible_nx_huge_pages);
+ list_add_tail(&sp->possible_nx_huge_page_link, pages);
}

static void account_nx_huge_page(struct kvm *kvm, struct kvm_mmu_page *sp,
@@ -881,7 +882,10 @@ static void account_nx_huge_page(struct kvm *kvm, struct kvm_mmu_page *sp,
sp->nx_huge_page_disallowed = true;

if (nx_huge_page_possible)
- track_possible_nx_huge_page(kvm, sp);
+ track_possible_nx_huge_page(kvm,
+ sp,
+ &kvm->arch.possible_nx_huge_pages,
+ &kvm->arch.nr_possible_nx_huge_pages);
}

static void unaccount_shadowed(struct kvm *kvm, struct kvm_mmu_page *sp)
@@ -900,11 +904,13 @@ static void unaccount_shadowed(struct kvm *kvm, struct kvm_mmu_page *sp)
kvm_mmu_gfn_allow_lpage(slot, gfn);
}

-void untrack_possible_nx_huge_page(struct kvm *kvm, struct kvm_mmu_page *sp)
+void untrack_possible_nx_huge_page(struct kvm *kvm, struct kvm_mmu_page *sp,
+ u64 *nr_pages)
{
if (list_empty(&sp->possible_nx_huge_page_link))
return;

+ --(*nr_pages);
--kvm->stat.nx_lpage_splits;
list_del_init(&sp->possible_nx_huge_page_link);
}
@@ -913,7 +919,7 @@ static void unaccount_nx_huge_page(struct kvm *kvm, struct kvm_mmu_page *sp)
{
sp->nx_huge_page_disallowed = false;

- untrack_possible_nx_huge_page(kvm, sp);
+ untrack_possible_nx_huge_page(kvm, sp, &kvm->arch.nr_possible_nx_huge_pages);
}

static struct kvm_memory_slot *gfn_to_memslot_dirty_bitmap(struct kvm_vcpu *vcpu,
@@ -7311,9 +7317,9 @@ static int set_nx_huge_pages_recovery_param(const char *val, const struct kernel
return err;
}

-static void kvm_recover_nx_huge_pages(struct kvm *kvm)
+void kvm_recover_nx_huge_pages(struct kvm *kvm, struct list_head *pages,
+ unsigned long nr_pages)
{
- unsigned long nx_lpage_splits = kvm->stat.nx_lpage_splits;
struct kvm_memory_slot *slot;
int rcu_idx;
struct kvm_mmu_page *sp;
@@ -7333,9 +7339,9 @@ static void kvm_recover_nx_huge_pages(struct kvm *kvm)
rcu_read_lock();

ratio = READ_ONCE(nx_huge_pages_recovery_ratio);
- to_zap = ratio ? DIV_ROUND_UP(nx_lpage_splits, ratio) : 0;
+ to_zap = ratio ? DIV_ROUND_UP(nr_pages, ratio) : 0;
for ( ; to_zap; --to_zap) {
- if (list_empty(&kvm->arch.possible_nx_huge_pages))
+ if (list_empty(pages))
break;

/*
@@ -7345,7 +7351,7 @@ static void kvm_recover_nx_huge_pages(struct kvm *kvm)
* the total number of shadow pages. And because the TDP MMU
* doesn't use active_mmu_pages.
*/
- sp = list_first_entry(&kvm->arch.possible_nx_huge_pages,
+ sp = list_first_entry(pages,
struct kvm_mmu_page,
possible_nx_huge_page_link);
WARN_ON_ONCE(!sp->nx_huge_page_disallowed);
@@ -7417,6 +7423,12 @@ static long get_nx_huge_page_recovery_timeout(u64 start_time)
: MAX_SCHEDULE_TIMEOUT;
}

+static void kvm_mmu_recover_nx_huge_pages(struct kvm *kvm)
+{
+ kvm_recover_nx_huge_pages(kvm, &kvm->arch.possible_nx_huge_pages,
+ kvm->arch.nr_possible_nx_huge_pages);
+}
+
static int kvm_nx_huge_page_recovery_worker(struct kvm *kvm, uintptr_t data)
{
u64 start_time;
@@ -7438,7 +7450,10 @@ static int kvm_nx_huge_page_recovery_worker(struct kvm *kvm, uintptr_t data)
if (kthread_should_stop())
return 0;

- kvm_recover_nx_huge_pages(kvm);
+ kvm_mmu_recover_nx_huge_pages(kvm);
+ if (tdp_mmu_enabled)
+ kvm_tdp_mmu_recover_nx_huge_pages(kvm);
+
}
}

diff --git a/arch/x86/kvm/mmu/mmu_internal.h b/arch/x86/kvm/mmu/mmu_internal.h
index 1721d97743e9..2d2e1231996a 100644
--- a/arch/x86/kvm/mmu/mmu_internal.h
+++ b/arch/x86/kvm/mmu/mmu_internal.h
@@ -351,7 +351,11 @@ void disallowed_hugepage_adjust(struct kvm_page_fault *fault, u64 spte, int cur_

void *mmu_memory_cache_alloc(struct kvm_mmu_memory_cache *mc);

-void track_possible_nx_huge_page(struct kvm *kvm, struct kvm_mmu_page *sp);
-void untrack_possible_nx_huge_page(struct kvm *kvm, struct kvm_mmu_page *sp);
+void track_possible_nx_huge_page(struct kvm *kvm, struct kvm_mmu_page *sp,
+ struct list_head *pages, u64 *nr_pages);
+void untrack_possible_nx_huge_page(struct kvm *kvm, struct kvm_mmu_page *sp,
+ u64 *nr_pages);
+void kvm_recover_nx_huge_pages(struct kvm *kvm, struct list_head *pages,
+ unsigned long nr_pages);

#endif /* __KVM_X86_MMU_INTERNAL_H */
diff --git a/arch/x86/kvm/mmu/tdp_mmu.c b/arch/x86/kvm/mmu/tdp_mmu.c
index c7dc49ee7388..9a6c26d20210 100644
--- a/arch/x86/kvm/mmu/tdp_mmu.c
+++ b/arch/x86/kvm/mmu/tdp_mmu.c
@@ -15,6 +15,7 @@
void kvm_mmu_init_tdp_mmu(struct kvm *kvm)
{
INIT_LIST_HEAD(&kvm->arch.tdp_mmu_roots);
+ INIT_LIST_HEAD(&kvm->arch.tdp_mmu_possible_nx_huge_pages);
spin_lock_init(&kvm->arch.tdp_mmu_pages_lock);
}

@@ -73,6 +74,13 @@ static void tdp_mmu_free_sp_rcu_callback(struct rcu_head *head)
tdp_mmu_free_sp(sp);
}

+void kvm_tdp_mmu_recover_nx_huge_pages(struct kvm *kvm)
+{
+ kvm_recover_nx_huge_pages(kvm,
+ &kvm->arch.tdp_mmu_possible_nx_huge_pages,
+ kvm->arch.tdp_mmu_nr_possible_nx_huge_pages);
+}
+
void kvm_tdp_mmu_put_root(struct kvm *kvm, struct kvm_mmu_page *root)
{
if (!refcount_dec_and_test(&root->tdp_mmu_root_count))
@@ -318,7 +326,7 @@ static void tdp_mmu_unlink_sp(struct kvm *kvm, struct kvm_mmu_page *sp)

spin_lock(&kvm->arch.tdp_mmu_pages_lock);
sp->nx_huge_page_disallowed = false;
- untrack_possible_nx_huge_page(kvm, sp);
+ untrack_possible_nx_huge_page(kvm, sp, &kvm->arch.tdp_mmu_nr_possible_nx_huge_pages);
spin_unlock(&kvm->arch.tdp_mmu_pages_lock);
}

@@ -1162,10 +1170,13 @@ int kvm_tdp_mmu_map(struct kvm_vcpu *vcpu, struct kvm_page_fault *fault)
}

if (fault->huge_page_disallowed &&
- fault->req_level >= iter.level) {
+ fault->req_level >= iter.level &&
+ sp->nx_huge_page_disallowed) {
spin_lock(&kvm->arch.tdp_mmu_pages_lock);
- if (sp->nx_huge_page_disallowed)
- track_possible_nx_huge_page(kvm, sp);
+ track_possible_nx_huge_page(kvm,
+ sp,
+ &kvm->arch.tdp_mmu_possible_nx_huge_pages,
+ &kvm->arch.tdp_mmu_nr_possible_nx_huge_pages);
spin_unlock(&kvm->arch.tdp_mmu_pages_lock);
}
}
diff --git a/arch/x86/kvm/mmu/tdp_mmu.h b/arch/x86/kvm/mmu/tdp_mmu.h
index 1b74e058a81c..510baf3eb3f1 100644
--- a/arch/x86/kvm/mmu/tdp_mmu.h
+++ b/arch/x86/kvm/mmu/tdp_mmu.h
@@ -66,6 +66,7 @@ int kvm_tdp_mmu_get_walk(struct kvm_vcpu *vcpu, u64 addr, u64 *sptes,
int *root_level);
u64 *kvm_tdp_mmu_fast_pf_get_last_sptep(struct kvm_vcpu *vcpu, gfn_t gfn,
u64 *spte);
+void kvm_tdp_mmu_recover_nx_huge_pages(struct kvm *kvm);

#ifdef CONFIG_X86_64
static inline bool is_tdp_mmu_page(struct kvm_mmu_page *sp) { return sp->tdp_mmu_page; }
--
2.46.0.469.g59c65b2a67-goog