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KVM: s390: Properly lock mm context allow_gmap_hpage_1m setting

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We have to do down_write on the mm semaphore to set a bitfield in the
mm context.

Signed-off-by: Janosch Frank <frankja@linux.ibm.com>
Fixes: a4499382 ("KVM: s390: Add huge page enablement control")
Reviewed-by: Christian Borntraeger <borntraeger@de.ibm.com>
Signed-off-by: Christian Borntraeger <borntraeger@de.ibm.com>
This commit is contained in:
Janosch Frank 2018-08-30 16:14:18 +02:00 committed by Christian Borntraeger
parent 204c972456
commit df88f3181f
2 changed files with 9 additions and 1 deletions
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8
arch/s390/include/asm/mmu.h
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@ -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;

2
arch/s390/kvm/kvm-s390.c
View File

@ -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