KVM: x86/mmu: Move the lockdep_assert of mmu_lock to inside clear_dirty_pt_masked()

Commit Message

Like Xu June 27, 2023, 4:26 a.m. UTC

From: Like Xu <[e-mail]>

Move the lockdep_assert_held_write(&kvm->mmu_lock) from the only one caller
kvm_tdp_mmu_clear_dirty_pt_masked() to inside clear_dirty_pt_masked().

This change makes it more obvious why it's safe for clear_dirty_pt_masked()
to use the non-atomic (for non-volatile SPTEs) tdp_mmu_clear_spte_bits()
helper. for_each_tdp_mmu_root() does its own lockdep, so the only "loss"
in lockdep coverage is if the list is completely empty.

Suggested-by: Sean Christopherson <[e-mail]>
Signed-off-by: Like Xu <[e-mail]>
---
 arch/x86/kvm/mmu/tdp_mmu.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)


base-commit: 88bb466c9dec4f70d682cf38c685324e7b1b3d60

Comments

Sean Christopherson Aug. 2, 2023, 7:17 p.m. UTC | #1

On Tue, 27 Jun 2023 12:26:39 +0800, Like Xu wrote:
> Move the lockdep_assert_held_write(&kvm->mmu_lock) from the only one caller
> kvm_tdp_mmu_clear_dirty_pt_masked() to inside clear_dirty_pt_masked().
> 
> This change makes it more obvious why it's safe for clear_dirty_pt_masked()
> to use the non-atomic (for non-volatile SPTEs) tdp_mmu_clear_spte_bits()
> helper. for_each_tdp_mmu_root() does its own lockdep, so the only "loss"
> in lockdep coverage is if the list is completely empty.
> 
> [...]

Applied to kvm-x86 mmu, thanks!

[1/1] KVM: x86/mmu: Move the lockdep_assert of mmu_lock to inside clear_dirty_pt_masked()
      https://github.com/kvm-x86/linux/commit/e19314998321

--
https://github.com/kvm-x86/linux/tree/next
https://github.com/kvm-x86/linux/tree/fixes

Patch

diff --git a/arch/x86/kvm/mmu/tdp_mmu.c b/arch/x86/kvm/mmu/tdp_mmu.c
index 512163d52194..0b4f03bef70e 100644
--- a/arch/x86/kvm/mmu/tdp_mmu.c
+++ b/arch/x86/kvm/mmu/tdp_mmu.c
@@ -1600,6 +1600,8 @@  static void clear_dirty_pt_masked(struct kvm *kvm, struct kvm_mmu_page *root,
 						   shadow_dirty_mask;
 	struct tdp_iter iter;
 
+	lockdep_assert_held_write(&kvm->mmu_lock);
+
 	rcu_read_lock();
 
 	tdp_root_for_each_leaf_pte(iter, root, gfn + __ffs(mask),
@@ -1646,7 +1648,6 @@  void kvm_tdp_mmu_clear_dirty_pt_masked(struct kvm *kvm,
 {
 	struct kvm_mmu_page *root;
 
-	lockdep_assert_held_write(&kvm->mmu_lock);
 	for_each_tdp_mmu_root(kvm, root, slot->as_id)
 		clear_dirty_pt_masked(kvm, root, gfn, mask, wrprot);
 }