Patch "kvm: arm/arm64: Fix locking for kvm_free_stage2_pgd" has been added to the 4.9-stable tree

This is a note to let you know that I've just added the patch titled

kvm: arm/arm64: Fix locking for kvm_free_stage2_pgd

to the 4.9-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
kvm-arm-arm64-fix-locking-for-kvm_free_stage2_pgd.patch
and it can be found in the queue-4.9 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Suzuki K Poulose <[email protected]>
Date: Mon, 3 Apr 2017 15:12:43 +0100
Subject: kvm: arm/arm64: Fix locking for kvm_free_stage2_pgd

From: Suzuki K Poulose <[email protected]>

commit 8b3405e345b5a098101b0c31b264c812bba045d9 upstream.

In kvm_free_stage2_pgd() we don't hold the kvm->mmu_lock while calling unmap_stage2_range() on the entire memory range for the guest. This could cause problems with other callers (e.g, munmap on a memslot) trying to unmap a range. And since we have to unmap the entire Guest memory range holding a spinlock, make sure we yield the lock if necessary, after we unmap each PUD range.

---
 arch/arm/kvm/mmu.c |   10 ++++++++++
 1 file changed, 10 insertions(+)

@@ -292,11 +292,18 @@ static void unmap_stage2_range(struct kv
 	phys_addr_t addr = start, end = start + size;
 	phys_addr_t next;
 
+	assert_spin_locked(&kvm->mmu_lock);
 	pgd = kvm->arch.pgd + stage2_pgd_index(addr);
 	do {
 		next = stage2_pgd_addr_end(addr, end);
 		if (!stage2_pgd_none(*pgd))
 			unmap_stage2_puds(kvm, pgd, addr, next);
+		/*
+		 * If the range is too large, release the kvm->mmu_lock
+		 * to prevent starvation and lockup detector warnings.
+		 */
+		if (next != end)
+			cond_resched_lock(&kvm->mmu_lock);
 	} while (pgd++, addr = next, addr != end);
 }
 

@@ -831,7 +838,10 @@ void kvm_free_stage2_pgd(struct kvm *kvm
 	if (kvm->arch.pgd == NULL)
 		return;
 
+	spin_lock(&kvm->mmu_lock);
 	unmap_stage2_range(kvm, 0, KVM_PHYS_SIZE);
+	spin_unlock(&kvm->mmu_lock);
+
 	/* Free the HW pgd, one page at a time */
 	free_pages_exact(kvm->arch.pgd, S2_PGD_SIZE);
 	kvm->arch.pgd = NULL;

Patches currently in stable-queue which might be from [email protected] are

queue-4.9/kvm-arm-arm64-fix-locking-for-kvm_free_stage2_pgd.patch queue-4.9/arm-arm64-kvm-take-mmap_sem-in-kvm_arch_prepare_memory_region.patch queue-4.9/arm-arm64-kvm-take-mmap_sem-in-stage2_unmap_vm.patch