We have to do down_write on the mm semaphore to set a bitfield in the
mm context.
Signed-off-by: Janosch Frank <frankja@xxxxxxxxxxxxx>
Fixes: a4499382 ("KVM: s390: Add huge page enablement control")
---
arch/s390/include/asm/mmu.h | 8 +++++++-
arch/s390/kvm/kvm-s390.c | 2 ++
2 files changed, 9 insertions(+), 1 deletion(-)
diff --git a/arch/s390/include/asm/mmu.h b/arch/s390/include/asm/mmu.h
index f31a15044c24..a8418e1379eb 100644
--- a/arch/s390/include/asm/mmu.h
+++ b/arch/s390/include/asm/mmu.h
@@ -16,7 +16,13 @@ typedef struct {
unsigned long asce;
unsigned long asce_limit;
unsigned long vdso_base;
- /* The mmu context allocates 4K page tables. */
+ /*
+ * The following bitfields need a down_write on the mm
+ * semaphore when they are written to. As they are only
+ * written once, they can be read without a lock.
+ *
+ * The mmu context allocates 4K page tables.
+ */
unsigned int alloc_pgste:1;
/* The mmu context uses extended page tables. */
unsigned int has_pgste:1;
diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c
index 8c039e12cb24..ac5da6b0b862 100644
--- a/arch/s390/kvm/kvm-s390.c
+++ b/arch/s390/kvm/kvm-s390.c
@@ -695,7 +695,9 @@ static int kvm_vm_ioctl_enable_cap(struct kvm *kvm, struct kvm_enable_cap *cap)
r = -EINVAL;
else {
r = 0;
+ down_write(&kvm->mm->mmap_sem);
kvm->mm->context.allow_gmap_hpage_1m = 1;
+ up_write(&kvm->mm->mmap_sem);
/*
* We might have to create fake 4k page
* tables. To avoid that the hardware works on
--
2.14.3
