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-rw-r--r--Documentation/virt/kvm/locking.rst8
-rw-r--r--arch/x86/include/asm/kvm_host.h7
-rw-r--r--arch/x86/kvm/mmu/mmu.c28
3 files changed, 39 insertions, 4 deletions
diff --git a/Documentation/virt/kvm/locking.rst b/Documentation/virt/kvm/locking.rst
index 35eca377543d..88fa495abbac 100644
--- a/Documentation/virt/kvm/locking.rst
+++ b/Documentation/virt/kvm/locking.rst
@@ -25,10 +25,10 @@ On x86:
- vcpu->mutex is taken outside kvm->arch.hyperv.hv_lock
-- kvm->arch.mmu_lock is an rwlock. kvm->arch.tdp_mmu_pages_lock is
- taken inside kvm->arch.mmu_lock, and cannot be taken without already
- holding kvm->arch.mmu_lock (typically with ``read_lock``, otherwise
- there's no need to take kvm->arch.tdp_mmu_pages_lock at all).
+- kvm->arch.mmu_lock is an rwlock. kvm->arch.tdp_mmu_pages_lock and
+ kvm->arch.mmu_unsync_pages_lock are taken inside kvm->arch.mmu_lock, and
+ cannot be taken without already holding kvm->arch.mmu_lock (typically with
+ ``read_lock`` for the TDP MMU, thus the need for additional spinlocks).
Everything else is a leaf: no other lock is taken inside the critical
sections.
diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index 974cbfb1eefe..af6ce8d4c86a 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -1038,6 +1038,13 @@ struct kvm_arch {
struct list_head lpage_disallowed_mmu_pages;
struct kvm_page_track_notifier_node mmu_sp_tracker;
struct kvm_page_track_notifier_head track_notifier_head;
+ /*
+ * Protects marking pages unsync during page faults, as TDP MMU page
+ * faults only take mmu_lock for read. For simplicity, the unsync
+ * pages lock is always taken when marking pages unsync regardless of
+ * whether mmu_lock is held for read or write.
+ */
+ spinlock_t mmu_unsync_pages_lock;
struct list_head assigned_dev_head;
struct iommu_domain *iommu_domain;
diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
index c4f4fa23320e..47b765270239 100644
--- a/arch/x86/kvm/mmu/mmu.c
+++ b/arch/x86/kvm/mmu/mmu.c
@@ -2535,6 +2535,7 @@ static void kvm_unsync_page(struct kvm_vcpu *vcpu, struct kvm_mmu_page *sp)
int mmu_try_to_unsync_pages(struct kvm_vcpu *vcpu, gfn_t gfn, bool can_unsync)
{
struct kvm_mmu_page *sp;
+ bool locked = false;
/*
* Force write-protection if the page is being tracked. Note, the page
@@ -2557,9 +2558,34 @@ int mmu_try_to_unsync_pages(struct kvm_vcpu *vcpu, gfn_t gfn, bool can_unsync)
if (sp->unsync)
continue;
+ /*
+ * TDP MMU page faults require an additional spinlock as they
+ * run with mmu_lock held for read, not write, and the unsync
+ * logic is not thread safe. Take the spinklock regardless of
+ * the MMU type to avoid extra conditionals/parameters, there's
+ * no meaningful penalty if mmu_lock is held for write.
+ */
+ if (!locked) {
+ locked = true;
+ spin_lock(&vcpu->kvm->arch.mmu_unsync_pages_lock);
+
+ /*
+ * Recheck after taking the spinlock, a different vCPU
+ * may have since marked the page unsync. A false
+ * positive on the unprotected check above is not
+ * possible as clearing sp->unsync _must_ hold mmu_lock
+ * for write, i.e. unsync cannot transition from 0->1
+ * while this CPU holds mmu_lock for read (or write).
+ */
+ if (READ_ONCE(sp->unsync))
+ continue;
+ }
+
WARN_ON(sp->role.level != PG_LEVEL_4K);
kvm_unsync_page(vcpu, sp);
}
+ if (locked)
+ spin_unlock(&vcpu->kvm->arch.mmu_unsync_pages_lock);
/*
* We need to ensure that the marking of unsync pages is visible
@@ -5537,6 +5563,8 @@ void kvm_mmu_init_vm(struct kvm *kvm)
{
struct kvm_page_track_notifier_node *node = &kvm->arch.mmu_sp_tracker;
+ spin_lock_init(&kvm->arch.mmu_unsync_pages_lock);
+
if (!kvm_mmu_init_tdp_mmu(kvm))
/*
* No smp_load/store wrappers needed here as we are in