KVM: Drop .on_unlock() mmu_notifier hook

Drop the .on_unlock() mmu_notifer hook now that it's no longer used for
notifying arch code that memory has been reclaimed.  Adding .on_unlock()
and invoking it *after* dropping mmu_lock was a terrible idea, as doing so
resulted in .on_lock() and .on_unlock() having divergent and asymmetric
behavior, and set future developers up for failure, i.e. all but asked for
bugs where KVM relied on using .on_unlock() to try to run a callback while
holding mmu_lock.

Opportunistically add a lockdep assertion in kvm_mmu_invalidate_end() to
guard against future bugs of this nature.

Reported-by: Isaku Yamahata <isaku.yamahata@intel.com>
Link: https://lore.kernel.org/all/20230802203119.GB2021422@ls.amr.corp.intel.com
Signed-off-by: Sean Christopherson <seanjc@google.com>
Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>
Reviewed-by: Fuad Tabba <tabba@google.com>
Tested-by: Fuad Tabba <tabba@google.com>
Message-Id: <20231027182217.3615211-12-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index e18a7f152c0b47a7fabad5f4aa50e4d25bc9d4e1..7f3291dec7a6cab7fb1db08bf1808866d34ceb3c 100644 (file)
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -544,7 +544,6 @@ static inline struct kvm *mmu_notifier_to_kvm(struct mmu_notifier *mn)
 typedef bool (*gfn_handler_t)(struct kvm *kvm, struct kvm_gfn_range *range);
 
 typedef void (*on_lock_fn_t)(struct kvm *kvm);
-typedef void (*on_unlock_fn_t)(struct kvm *kvm);
 
 struct kvm_mmu_notifier_range {
        /*
@@ -556,7 +555,6 @@ struct kvm_mmu_notifier_range {
        union kvm_mmu_notifier_arg arg;
        gfn_handler_t handler;
        on_lock_fn_t on_lock;
-       on_unlock_fn_t on_unlock;
        bool flush_on_ret;
        bool may_block;
 };
@@ -663,11 +661,8 @@ static __always_inline kvm_mn_ret_t __kvm_handle_hva_range(struct kvm *kvm,
        if (range->flush_on_ret && r.ret)
                kvm_flush_remote_tlbs(kvm);
 
-       if (r.found_memslot) {
+       if (r.found_memslot)
                KVM_MMU_UNLOCK(kvm);
-               if (!IS_KVM_NULL_FN(range->on_unlock))
-                       range->on_unlock(kvm);
-       }
 
        srcu_read_unlock(&kvm->srcu, idx);
 
@@ -687,7 +682,6 @@ static __always_inline int kvm_handle_hva_range(struct mmu_notifier *mn,
                .arg            = arg,
                .handler        = handler,
                .on_lock        = (void *)kvm_null_fn,
-               .on_unlock      = (void *)kvm_null_fn,
                .flush_on_ret   = true,
                .may_block      = false,
        };
@@ -706,7 +700,6 @@ static __always_inline int kvm_handle_hva_range_no_flush(struct mmu_notifier *mn
                .end            = end,
                .handler        = handler,
                .on_lock        = (void *)kvm_null_fn,
-               .on_unlock      = (void *)kvm_null_fn,
                .flush_on_ret   = false,
                .may_block      = false,
        };
@@ -813,7 +806,6 @@ static int kvm_mmu_notifier_invalidate_range_start(struct mmu_notifier *mn,
                .end            = range->end,
                .handler        = kvm_mmu_unmap_gfn_range,
                .on_lock        = kvm_mmu_invalidate_begin,
-               .on_unlock      = (void *)kvm_null_fn,
                .flush_on_ret   = true,
                .may_block      = mmu_notifier_range_blockable(range),
        };
@@ -891,7 +883,6 @@ static void kvm_mmu_notifier_invalidate_range_end(struct mmu_notifier *mn,
                .end            = range->end,
                .handler        = (void *)kvm_null_fn,
                .on_lock        = kvm_mmu_invalidate_end,
-               .on_unlock      = (void *)kvm_null_fn,
                .flush_on_ret   = false,
                .may_block      = mmu_notifier_range_blockable(range),
        };