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Commit 3a801517 authored by Martin Schwidefsky's avatar Martin Schwidefsky Committed by Christian Borntraeger
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KVM: s390: correct locking for s390_enable_skey 



Use the mm semaphore to serialize multiple invocations of s390_enable_skey.
The second CPU faulting on a storage key operation needs to wait for the
completion of the page table update. Taking the mm semaphore writable
has the positive side-effect that it prevents any host faults from
taking place which does have implications on keys vs PGSTE.

Signed-off-by: default avatarMartin Schwidefsky <schwidefsky@de.ibm.com>
Signed-off-by: default avatarChristian Borntraeger <borntraeger@de.ibm.com>
parent d9f89b88

arch/s390/mm/pgtable.c

+7 −15
Original line number Diff line number Diff line
@@ -958,8 +958,10 @@ void page_table_reset_pgste(struct mm_struct *mm, unsigned long start, 
	unsigned long addr, next;

	pgd_t *pgd;



	down_write(&mm->mmap_sem);

	if (init_skey && mm_use_skey(mm))

		goto out_up;

	addr = start;

	down_read(&mm->mmap_sem);

	pgd = pgd_offset(mm, addr);

	do {

		next = pgd_addr_end(addr, end);
@@ -967,7 +969,10 @@ void page_table_reset_pgste(struct mm_struct *mm, unsigned long start, 
			continue;

		next = page_table_reset_pud(mm, pgd, addr, next, init_skey);

	} while (pgd++, addr = next, addr != end);

	up_read(&mm->mmap_sem);

	if (init_skey)

		current->mm->context.use_skey = 1;

out_up:

	up_write(&mm->mmap_sem);

}

EXPORT_SYMBOL(page_table_reset_pgste);
@@ -1384,19 +1389,6 @@ EXPORT_SYMBOL_GPL(s390_enable_sie); 
 */

void s390_enable_skey(void)

{

	/*

	 * To avoid races between multiple vcpus, ending in calling

	 * page_table_reset twice or more,

	 * the page_table_lock is taken for serialization.

	 */

	spin_lock(&current->mm->page_table_lock);

	if (mm_use_skey(current->mm)) {

		spin_unlock(&current->mm->page_table_lock);

		return;

	}



	current->mm->context.use_skey = 1;

	spin_unlock(&current->mm->page_table_lock);

	page_table_reset_pgste(current->mm, 0, TASK_SIZE, true);

}

EXPORT_SYMBOL_GPL(s390_enable_skey);