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FAILED: patch "[PATCH] kvm: arm/arm64: Fix locking for kvm_free_stage2_pgd" failed to apply to 4.4-stable tree

PATCH [email protected] 1 participant 1 message Apr 9, 2017

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Stable branch Arm (32-bit)
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The patch below does not apply to the 4.4-stable tree.
If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to <[email protected]>.

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

Quoted 1 line

From 8b3405e345b5a098101b0c31b264c812bba045d9 Mon Sep 17 00:00:00 2001

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

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.

Fixes commit d5d8184d35c9 ("KVM: ARM: Memory virtualization setup")
Cc [email protected] # v3.10+
Cc Paolo Bonzini <[email protected]>
Cc Marc Zyngier <[email protected]>
Cc Christoffer Dall <[email protected]>
Cc Mark Rutland <[email protected]>
Signed-off-by Suzuki K Poulose <[email protected]>
[ Avoid vCPU starvation and lockup detector warnings ]
Signed-off-by Marc Zyngier <[email protected]>
Signed-off-by Suzuki K Poulose <[email protected]>
Signed-off-by Christoffer Dall <[email protected]>
arch/arm/kvm/mmu.c +10 -0
index 13b9c1fa8961..582a972371cf 100644
@@ -292,11 +292,18 @@ static void unmap_stage2_range(struct kvm *kvm, phys_addr_t start, u64 size)
 	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;