[PATCH 1/5] KVM: riscv: Rely on common MMU notifier locking

[Jinyu Tang <tjytimi@163.com>]

The common KVM invalidation paths call kvm_unmap_gfn_range() with
mmu_lock already held for write.

For the standard MMU notifier path, the call chain is:

  kvm_mmu_notifier_invalidate_range_start()
    kvm_handle_hva_range()
      kvm_unmap_gfn_range()

kvm_mmu_notifier_invalidate_range_start() leaves range.lockless clear.
kvm_handle_hva_range() therefore takes KVM_MMU_LOCK(kvm) before invoking
the handler.

The guest_memfd path has the same locking contract:

  __kvm_gmem_invalidate_begin()
    kvm_mmu_unmap_gfn_range()
      kvm_unmap_gfn_range()

__kvm_gmem_invalidate_begin() explicitly takes KVM_MMU_LOCK(kvm) before
calling kvm_mmu_unmap_gfn_range().

So remove the local trylock and make the common locking contract explicit 
with lockdep_assert_held_write() like x86.

Signed-off-by: Jinyu Tang <tjytimi@163.com>
---
 arch/riscv/kvm/mmu.c | 6 ++----
 1 file changed, 2 insertions(+), 4 deletions(-)

diff --git a/arch/riscv/kvm/mmu.c b/arch/riscv/kvm/mmu.c
index 2d3def024..0197e41fc 100644
--- a/arch/riscv/kvm/mmu.c
+++ b/arch/riscv/kvm/mmu.c
@@ -230,18 +230,16 @@ int kvm_arch_prepare_memory_region(struct kvm *kvm,
 bool kvm_unmap_gfn_range(struct kvm *kvm, struct kvm_gfn_range *range)
 {
 	struct kvm_gstage gstage;
-	bool mmu_locked;
 
 	if (!kvm->arch.pgd)
 		return false;
 
+	lockdep_assert_held_write(&kvm->mmu_lock);
+
 	kvm_riscv_gstage_init(&gstage, kvm);
-	mmu_locked = spin_trylock(&kvm->mmu_lock);
 	kvm_riscv_gstage_unmap_range(&gstage, range->start << PAGE_SHIFT,
 				     (range->end - range->start) << PAGE_SHIFT,
 				     range->may_block);
-	if (mmu_locked)
-		spin_unlock(&kvm->mmu_lock);
 	return false;
 }
 
-- 
2.43.0