--- /dev/null
+From b5331379bc62611d1026173a09c73573384201d9 Mon Sep 17 00:00:00 2001
+From: Will Deacon <will@kernel.org>
+Date: Tue, 11 Aug 2020 11:27:25 +0100
+Subject: KVM: arm64: Only reschedule if MMU_NOTIFIER_RANGE_BLOCKABLE is not set
+
+From: Will Deacon <will@kernel.org>
+
+commit b5331379bc62611d1026173a09c73573384201d9 upstream.
+
+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: 8b3405e345b5 ("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>
+Signed-off-by: Will Deacon <will@kernel.org>
+Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
+---
+ arch/arm64/kvm/mmu.c | 17 +++++++++++++----
+ 1 file changed, 13 insertions(+), 4 deletions(-)
+
+--- a/arch/arm64/kvm/mmu.c
++++ b/arch/arm64/kvm/mmu.c
+@@ -365,7 +365,8 @@ static void unmap_stage2_p4ds(struct kvm
+ * destroying the VM), otherwise another faulting VCPU may come in and mess
+ * with things behind our backs.
+ */
+-static void unmap_stage2_range(struct kvm *kvm, phys_addr_t start, u64 size)
++static void __unmap_stage2_range(struct kvm *kvm, phys_addr_t start, u64 size,
++ bool may_block)
+ {
+ pgd_t *pgd;
+ phys_addr_t addr = start, end = start + size;
+@@ -390,11 +391,16 @@ static void unmap_stage2_range(struct kv
+ * 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 *kvm, phys_addr_t start, u64 size)
++{
++ __unmap_stage2_range(kvm, start, size, true);
++}
++
+ static void stage2_flush_ptes(struct kvm *kvm, pmd_t *pmd,
+ phys_addr_t addr, phys_addr_t end)
+ {
+@@ -2198,7 +2204,10 @@ static int handle_hva_to_gpa(struct kvm
+
+ static int kvm_unmap_hva_handler(struct kvm *kvm, gpa_t gpa, u64 size, void *data)
+ {
+- unmap_stage2_range(kvm, gpa, size);
++ unsigned flags = *(unsigned *)data;
++ bool may_block = flags & MMU_NOTIFIER_RANGE_BLOCKABLE;
++
++ __unmap_stage2_range(kvm, gpa, size, may_block);
+ return 0;
+ }
+
+@@ -2209,7 +2218,7 @@ 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;
+ }
+
projects / thirdparty / kernel / stable-queue.git / commitdiff
