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KVM: arm64: Only reschedule if MMU_NOTIFIER_RANGE_BLOCKABLE is not set

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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: 8b3405e345 ("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>
This commit is contained in:
Will Deacon 2020-08-11 11:27:25 +01:00 committed by Paolo Bonzini
parent fdfe7cbd58
commit b5331379bc
1 changed files with 13 additions and 4 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

17
arch/arm64/kvm/mmu.c
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@ -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;
}