linux-kernel - [PATCH v2] KVM: arm/arm64: Handle hva aging while destroying the vm

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Date:   Wed,  5 Jul 2017 08:20:31 +0200
From:   Alexander Graf <agraf@...e.de>
To:     kvmarm@...ts.cs.columbia.edu
Cc:     kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
        Christoffer Dall <cdall@...aro.org>,
        Andrea Arcangeli <aarcange@...hat.com>,
        Suzuki K Poulose <suzuki.poulose@....com>,
        stable@...r.kernel.org
Subject: [PATCH v2] KVM: arm/arm64: Handle hva aging while destroying the vm

The kvm_age_hva callback may be called all the way concurrently while
kvm_mmu_notifier_release() is running.

The release function sets kvm->arch.pgd = NULL which the aging function
however implicitly relies on in stage2_get_pud(). That means they can
race and the aging function may dereference a NULL pgd pointer.

This patch adds a check for that case, so that we leave the aging
function silently.

Cc: stable@...r.kernel.org
Fixes: 293f29363 ("kvm-arm: Unmap shadow pagetables properly")
Signed-off-by: Alexander Graf <agraf@...e.de>

---

v1 -> v2:

  - Fix commit message
  - Add Fixes and stable tags
---
 virt/kvm/arm/mmu.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/virt/kvm/arm/mmu.c b/virt/kvm/arm/mmu.c
index f2d5b6c..227931f 100644
--- a/virt/kvm/arm/mmu.c
+++ b/virt/kvm/arm/mmu.c
@@ -861,6 +861,10 @@ static pud_t *stage2_get_pud(struct kvm *kvm, struct kvm_mmu_memory_cache *cache
 	pgd_t *pgd;
 	pud_t *pud;
 
+	/* Do we clash with kvm_free_stage2_pgd()? */
+	if (!kvm->arch.pgd)
+		return NULL;
+
 	pgd = kvm->arch.pgd + stage2_pgd_index(addr);
 	if (WARN_ON(stage2_pgd_none(*pgd))) {
 		if (!cache)
-- 
1.8.5.6