Re: [PATCH 16/24] kvm: mmu: Wrap mmu_lock assertions

[Paolo Bonzini]

On 12/01/21 19:10, Ben Gardon wrote:
> Wrap assertions and warnings checking the MMU lock state in a function
> which uses lockdep_assert_held. While the existing checks use a few
> different functions to check the lock state, they are all better off
> using lockdep_assert_held. This will support a refactoring to move the
> mmu_lock to struct kvm_arch so that it can be replaced with an rwlock for
> x86.
>
> Reviewed-by: Peter Feiner <pfeiner@xxxxxxxxxx>
>
> Signed-off-by: Ben Gardon <bgardon@xxxxxxxxxx>
> ---
>   arch/arm64/kvm/mmu.c                     | 2 +-
>   arch/powerpc/include/asm/kvm_book3s_64.h | 7 +++----
>   arch/powerpc/kvm/book3s_hv_nested.c      | 3 +--
>   arch/x86/kvm/mmu/mmu_internal.h          | 4 ++--
>   arch/x86/kvm/mmu/tdp_mmu.c               | 8 ++++----
>   include/linux/kvm_host.h                 | 1 +
>   virt/kvm/kvm_main.c                      | 5 +++++
>   7 files changed, 17 insertions(+), 13 deletions(-)
>
> diff --git a/arch/arm64/kvm/mmu.c b/arch/arm64/kvm/mmu.c
> index 57ef1ec23b56..8b54eb58bf47 100644
> --- a/arch/arm64/kvm/mmu.c
> +++ b/arch/arm64/kvm/mmu.c
> @@ -130,7 +130,7 @@ static void __unmap_stage2_range(struct kvm_s2_mmu *mmu, phys_addr_t start, u64
>   	struct kvm *kvm = mmu->kvm;
>   	phys_addr_t end = start + size;
>   
> -	assert_spin_locked(&kvm->mmu_lock);
> +	kvm_mmu_lock_assert_held(kvm);
>   	WARN_ON(size & ~PAGE_MASK);
>   	WARN_ON(stage2_apply_range(kvm, start, end, kvm_pgtable_stage2_unmap,
>   				   may_block));
> diff --git a/arch/powerpc/include/asm/kvm_book3s_64.h b/arch/powerpc/include/asm/kvm_book3s_64.h
> index 9bb9bb370b53..db2e437cd97c 100644
> --- a/arch/powerpc/include/asm/kvm_book3s_64.h
> +++ b/arch/powerpc/include/asm/kvm_book3s_64.h
> @@ -650,8 +650,8 @@ static inline pte_t *find_kvm_secondary_pte(struct kvm *kvm, unsigned long ea,
>   {
>   	pte_t *pte;
>   
> -	VM_WARN(!spin_is_locked(&kvm->mmu_lock),
> -		"%s called with kvm mmu_lock not held \n", __func__);
> +	kvm_mmu_lock_assert_held(kvm);
> +
>   	pte = __find_linux_pte(kvm->arch.pgtable, ea, NULL, hshift);
>   
>   	return pte;
> @@ -662,8 +662,7 @@ static inline pte_t *find_kvm_host_pte(struct kvm *kvm, unsigned long mmu_seq,
>   {
>   	pte_t *pte;
>   
> -	VM_WARN(!spin_is_locked(&kvm->mmu_lock),
> -		"%s called with kvm mmu_lock not held \n", __func__);
> +	kvm_mmu_lock_assert_held(kvm);
>   
>   	if (mmu_notifier_retry(kvm, mmu_seq))
>   		return NULL;
> diff --git a/arch/powerpc/kvm/book3s_hv_nested.c b/arch/powerpc/kvm/book3s_hv_nested.c
> index 18890dca9476..6d5987d1eee7 100644
> --- a/arch/powerpc/kvm/book3s_hv_nested.c
> +++ b/arch/powerpc/kvm/book3s_hv_nested.c
> @@ -767,8 +767,7 @@ pte_t *find_kvm_nested_guest_pte(struct kvm *kvm, unsigned long lpid,
>   	if (!gp)
>   		return NULL;
>   
> -	VM_WARN(!spin_is_locked(&kvm->mmu_lock),
> -		"%s called with kvm mmu_lock not held \n", __func__);
> +	kvm_mmu_lock_assert_held(kvm);
>   	pte = __find_linux_pte(gp->shadow_pgtable, ea, NULL, hshift);
>   
>   	return pte;
> diff --git a/arch/x86/kvm/mmu/mmu_internal.h b/arch/x86/kvm/mmu/mmu_internal.h
> index 7f599cc64178..cc8268cf28d2 100644
> --- a/arch/x86/kvm/mmu/mmu_internal.h
> +++ b/arch/x86/kvm/mmu/mmu_internal.h
> @@ -101,14 +101,14 @@ void kvm_flush_remote_tlbs_with_address(struct kvm *kvm,
>   static inline void kvm_mmu_get_root(struct kvm *kvm, struct kvm_mmu_page *sp)
>   {
>   	BUG_ON(!sp->root_count);
> -	lockdep_assert_held(&kvm->mmu_lock);
> +	kvm_mmu_lock_assert_held(kvm);
>   
>   	++sp->root_count;
>   }
>   
>   static inline bool kvm_mmu_put_root(struct kvm *kvm, struct kvm_mmu_page *sp)
>   {
> -	lockdep_assert_held(&kvm->mmu_lock);
> +	kvm_mmu_lock_assert_held(kvm);
>   	--sp->root_count;
>   
>   	return !sp->root_count;
> diff --git a/arch/x86/kvm/mmu/tdp_mmu.c b/arch/x86/kvm/mmu/tdp_mmu.c
> index fb911ca428b2..1d7c01300495 100644
> --- a/arch/x86/kvm/mmu/tdp_mmu.c
> +++ b/arch/x86/kvm/mmu/tdp_mmu.c
> @@ -117,7 +117,7 @@ void kvm_tdp_mmu_free_root(struct kvm *kvm, struct kvm_mmu_page *root)
>   {
>   	gfn_t max_gfn = 1ULL << (shadow_phys_bits - PAGE_SHIFT);
>   
> -	lockdep_assert_held(&kvm->mmu_lock);
> +	kvm_mmu_lock_assert_held(kvm);
>   
>   	WARN_ON(root->root_count);
>   	WARN_ON(!root->tdp_mmu_page);
> @@ -425,7 +425,7 @@ static inline void __tdp_mmu_set_spte(struct kvm *kvm, struct tdp_iter *iter,
>   	struct kvm_mmu_page *root = sptep_to_sp(root_pt);
>   	int as_id = kvm_mmu_page_as_id(root);
>   
> -	lockdep_assert_held(&kvm->mmu_lock);
> +	kvm_mmu_lock_assert_held(kvm);
>   
>   	WRITE_ONCE(*iter->sptep, new_spte);
>   
> @@ -1139,7 +1139,7 @@ void kvm_tdp_mmu_clear_dirty_pt_masked(struct kvm *kvm,
>   	struct kvm_mmu_page *root;
>   	int root_as_id;
>   
> -	lockdep_assert_held(&kvm->mmu_lock);
> +	kvm_mmu_lock_assert_held(kvm);
>   	for_each_tdp_mmu_root(kvm, root) {
>   		root_as_id = kvm_mmu_page_as_id(root);
>   		if (root_as_id != slot->as_id)
> @@ -1324,7 +1324,7 @@ bool kvm_tdp_mmu_write_protect_gfn(struct kvm *kvm,
>   	int root_as_id;
>   	bool spte_set = false;
>   
> -	lockdep_assert_held(&kvm->mmu_lock);
> +	kvm_mmu_lock_assert_held(kvm);
>   	for_each_tdp_mmu_root(kvm, root) {
>   		root_as_id = kvm_mmu_page_as_id(root);
>   		if (root_as_id != slot->as_id)
> diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
> index 6e2773fc406c..022e3522788f 100644
> --- a/include/linux/kvm_host.h
> +++ b/include/linux/kvm_host.h
> @@ -1499,5 +1499,6 @@ void kvm_mmu_lock(struct kvm *kvm);
>   void kvm_mmu_unlock(struct kvm *kvm);
>   int kvm_mmu_lock_needbreak(struct kvm *kvm);
>   int kvm_mmu_lock_cond_resched(struct kvm *kvm);
> +void kvm_mmu_lock_assert_held(struct kvm *kvm);

Probably better to make this an empty inline if !defined(CONFIG_LOCKDEP).

Paolo

>   #endif
> diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
> index b4c49a7e0556..c504f876176b 100644
> --- a/virt/kvm/kvm_main.c
> +++ b/virt/kvm/kvm_main.c
> @@ -452,6 +452,11 @@ int kvm_mmu_lock_cond_resched(struct kvm *kvm)
>   	return cond_resched_lock(&kvm->mmu_lock);
>   }
>   
> +void kvm_mmu_lock_assert_held(struct kvm *kvm)
> +{
> +	lockdep_assert_held(&kvm->mmu_lock);
> +}
> +
>   #if defined(CONFIG_MMU_NOTIFIER) && defined(KVM_ARCH_WANT_MMU_NOTIFIER)
>   static inline struct kvm *mmu_notifier_to_kvm(struct mmu_notifier *mn)
>   {