diff mbox series

[v13,11/35] KVM: Drop .on_unlock() mmu_notifier hook

Message ID 20231027182217.3615211-12-seanjc@google.com (mailing list archive)
State New
Headers show
Series KVM: guest_memfd() and per-page attributes | expand

Commit Message

Sean Christopherson Oct. 27, 2023, 6:21 p.m. UTC
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>
---
 virt/kvm/kvm_main.c | 13 +++----------
 1 file changed, 3 insertions(+), 10 deletions(-)

Comments

Paolo Bonzini Oct. 30, 2023, 5:18 p.m. UTC | #1
On 10/27/23 20:21, Sean Christopherson wrote:
> 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.

This is what David suggested to do in patch 3, FWIW.

Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>

Paolo

> 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>
> ---
Fuad Tabba Nov. 2, 2023, 1:55 p.m. UTC | #2
On Fri, Oct 27, 2023 at 7:22 PM Sean Christopherson <seanjc@google.com> wrote:
>
> 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: Fuad Tabba <tabba@google.com>
Tested-by: Fuad Tabba <tabba@google.com>

Cheers,
/fuad

>  virt/kvm/kvm_main.c | 13 +++----------
>  1 file changed, 3 insertions(+), 10 deletions(-)
>
> diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
> index 2bc04c8ae1f4..cb9376833c18 100644
> --- 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),
>         };
> @@ -858,6 +850,8 @@ static int kvm_mmu_notifier_invalidate_range_start(struct mmu_notifier *mn,
>
>  void kvm_mmu_invalidate_end(struct kvm *kvm)
>  {
> +       lockdep_assert_held_write(&kvm->mmu_lock);
> +
>         /*
>          * This sequence increase will notify the kvm page fault that
>          * the page that is going to be mapped in the spte could have
> @@ -889,7 +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),
>         };
> --
> 2.42.0.820.g83a721a137-goog
>
diff mbox series

Patch

diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index 2bc04c8ae1f4..cb9376833c18 100644
--- 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),
 	};
@@ -858,6 +850,8 @@  static int kvm_mmu_notifier_invalidate_range_start(struct mmu_notifier *mn,
 
 void kvm_mmu_invalidate_end(struct kvm *kvm)
 {
+	lockdep_assert_held_write(&kvm->mmu_lock);
+
 	/*
 	 * This sequence increase will notify the kvm page fault that
 	 * the page that is going to be mapped in the spte could have
@@ -889,7 +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),
 	};