Commit b5331379 authored Aug 11, 2020 by Will Deacon Committed by Paolo Bonzini Aug 21, 2020

KVM: arm64: Only reschedule if MMU_NOTIFIER_RANGE_BLOCKABLE is not set



When an MMU notifier call results in unmapping a range that spans multiple
PGDs, we end up calling into cond_resched_lock() when crossing a PGD boundary,
since this avoids running into RCU stalls during VM teardown. Unfortunately,
if the VM is destroyed as a result of OOM, then blocking is not permitted
and the call to the scheduler triggers the following BUG():

 | BUG: sleeping function called from invalid context at arch/arm64/kvm/mmu.c:394
 | in_atomic(): 1, irqs_disabled(): 0, non_block: 1, pid: 36, name: oom_reaper
 | INFO: lockdep is turned off.
 | CPU: 3 PID: 36 Comm: oom_reaper Not tainted 5.8.0 #1
 | Hardware name: QEMU QEMU Virtual Machine, BIOS 0.0.0 02/06/2015
 | Call trace:
 |  dump_backtrace+0x0/0x284
 |  show_stack+0x1c/0x28
 |  dump_stack+0xf0/0x1a4
 |  ___might_sleep+0x2bc/0x2cc
 |  unmap_stage2_range+0x160/0x1ac
 |  kvm_unmap_hva_range+0x1a0/0x1c8
 |  kvm_mmu_notifier_invalidate_range_start+0x8c/0xf8
 |  __mmu_notifier_invalidate_range_start+0x218/0x31c
 |  mmu_notifier_invalidate_range_start_nonblock+0x78/0xb0
 |  __oom_reap_task_mm+0x128/0x268
 |  oom_reap_task+0xac/0x298
 |  oom_reaper+0x178/0x17c
 |  kthread+0x1e4/0x1fc
 |  ret_from_fork+0x10/0x30

Use the new 'flags' argument to kvm_unmap_hva_range() to ensure that we
only reschedule if MMU_NOTIFIER_RANGE_BLOCKABLE is set in the notifier
flags.

Cc: <stable@vger.kernel.org>
Fixes: 8b3405e3 ("kvm: arm/arm64: Fix locking for kvm_free_stage2_pgd")
Cc: Marc Zyngier <maz@kernel.org>
Cc: Suzuki K Poulose <suzuki.poulose@arm.com>
Cc: James Morse <james.morse@arm.com>
Signed-off-by: Will Deacon <will@kernel.org>
Message-Id: <20200811102725.7121-3-will@kernel.org>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

parent fdfe7cbd

arch/arm64/kvm/mmu.c

+13 −4

Original line number	Diff line number	Diff line
		@@ -343,7 +343,8 @@ static void unmap_stage2_p4ds(struct kvm_s2_mmu mmu, pgd_t pgd,
		* destroying the VM), otherwise another faulting VCPU may come in and mess
		* with things behind our backs.
		*/
		static void unmap_stage2_range(struct kvm_s2_mmu *mmu, phys_addr_t start, u64 size)
		static void __unmap_stage2_range(struct kvm_s2_mmu *mmu, phys_addr_t start, u64 size,
		bool may_block)
		{
		struct kvm *kvm = mmu->kvm;
		pgd_t *pgd;
		@@ -369,11 +370,16 @@ static void unmap_stage2_range(struct kvm_s2_mmu *mmu, phys_addr_t start, u64 si
		* If the range is too large, release the kvm->mmu_lock
		* to prevent starvation and lockup detector warnings.
		*/
		if (next != end)
		if (may_block && next != end)
		cond_resched_lock(&kvm->mmu_lock);
		} while (pgd++, addr = next, addr != end);
		}

		static void unmap_stage2_range(struct kvm_s2_mmu *mmu, phys_addr_t start, u64 size)
		{
		__unmap_stage2_range(mmu, start, size, true);
		}

		static void stage2_flush_ptes(struct kvm_s2_mmu mmu, pmd_t pmd,
		phys_addr_t addr, phys_addr_t end)
		{
		@@ -2208,7 +2214,10 @@ static int handle_hva_to_gpa(struct kvm *kvm,

		static int kvm_unmap_hva_handler(struct kvm kvm, gpa_t gpa, u64 size, void data)
		{
		unmap_stage2_range(&kvm->arch.mmu, gpa, size);
		unsigned flags = (unsigned )data;
		bool may_block = flags & MMU_NOTIFIER_RANGE_BLOCKABLE;

		__unmap_stage2_range(&kvm->arch.mmu, gpa, size, may_block);
		return 0;
		}

		@@ -2219,7 +2228,7 @@ int kvm_unmap_hva_range(struct kvm *kvm,
		return 0;

		trace_kvm_unmap_hva_range(start, end);
		handle_hva_to_gpa(kvm, start, end, &kvm_unmap_hva_handler, NULL);
		handle_hva_to_gpa(kvm, start, end, &kvm_unmap_hva_handler, &flags);
		return 0;
		}

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