The patch below does not apply to the 4.19-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 stable@vger.kernel.org.

thanks,

greg k-h

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

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: [PATCH] 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: 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

diff --git a/arch/arm64/kvm/mmu.c b/arch/arm64/kvm/mmu.c index dc351802ff18..ba00bcc0c884 100644 --- a/arch/arm64/kvm/mmu.c +++ b/arch/arm64/kvm/mmu.c @@ -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; }