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Subject[PATCH v3] kvm: arm/arm64: Fix locking for kvm_free_stage2_pgd
Date
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: stable@vger.kernel.org # v3.10+
Cc: Paolo Bonzini <pbonzin@redhat.com>
Cc: Marc Zyngier <marc.zyngier@arm.com>
Cc: Christoffer Dall <christoffer.dall@linaro.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Suzuki K Poulose <suzuki.poulose@arm.com>
[ Avoid vCPU starvation and lockup detector warnings ]
Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>
Signed-off-by: Suzuki K Poulose <suzuki.poulose@arm.com>

---
Changes since V2:
- Restrict kvm->mmu_lock relaxation to bigger ranges in unmap_stage2_range(),
to avoid possible issues like [0]

[0] http://lists.infradead.org/pipermail/linux-arm-kernel/2017-March/498210.html

Changes since V1:
- Yield the kvm->mmu_lock if necessary in unmap_stage2_range to prevent
vCPU starvation and lockup detector warnings.
---
arch/arm/kvm/mmu.c | 10 ++++++++++
1 file changed, 10 insertions(+)

diff --git a/arch/arm/kvm/mmu.c b/arch/arm/kvm/mmu.c
index 13b9c1f..db94f3a 100644
--- a/arch/arm/kvm/mmu.c
+++ b/arch/arm/kvm/mmu.c
@@ -292,8 +292,15 @@ 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 {
+ /*
+ * If the range is too large, release the kvm->mmu_lock
+ * to prevent starvation and lockup detector warnings.
+ */
+ if (size > S2_PUD_SIZE)
+ cond_resched_lock(&kvm->mmu_lock);
next = stage2_pgd_addr_end(addr, end);
if (!stage2_pgd_none(*pgd))
unmap_stage2_puds(kvm, pgd, addr, next);
@@ -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;
--
2.7.4
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