From 443a813304ec36d4e81264b6a452a412a6b3ad9b Mon Sep 17 00:00:00 2001 From: Martin Schwidefsky Date: Wed, 24 Feb 2016 10:18:50 +0100 Subject: [PATCH] s390/kvm: simplify set_guest_storage_key Git commit ab3f285f227fec62868037e9b1b1fd18294a83b8 "KVM: s390/mm: try a cow on read only pages for key ops" added a fixup_user_fault to set_guest_storage_key force a copy on write if the page is mapped read-only. This is supposed to fix the problem of differing storage keys for shared mappings, e.g. the empty_zero_page. But if the storage key is set before the pte is mapped the storage key update is done on the pgste. A later fault will happily map the shared page with the key from the pgste. Eventually git commit 2faee8ff9dc6f4bfe46f6d2d110add858140fb20 "s390/mm: prevent and break zero page mappings in case of storage keys" fixed this problem for the empty_zero_page. The commit makes sure that guests enabled for storage keys will not use the empty_zero_page at all. As the call to fixup_user_fault in set_guest_storage_key depends on the order of the storage key operation vs. the fault that maps the pte it does not really fix anything. Just remove it. Reviewed-by: Dominik Dingel Signed-off-by: Martin Schwidefsky --- arch/s390/mm/pgtable.c | 17 ----------------- 1 file changed, 17 deletions(-) diff --git a/arch/s390/mm/pgtable.c b/arch/s390/mm/pgtable.c index 5109827883ac..6acd7174fe75 100644 --- a/arch/s390/mm/pgtable.c +++ b/arch/s390/mm/pgtable.c @@ -809,30 +809,13 @@ int set_guest_storage_key(struct mm_struct *mm, unsigned long addr, spinlock_t *ptl; pgste_t old, new; pte_t *ptep; - bool unlocked; down_read(&mm->mmap_sem); -retry: - unlocked = false; ptep = get_locked_pte(mm, addr, &ptl); if (unlikely(!ptep)) { up_read(&mm->mmap_sem); return -EFAULT; } - if (!(pte_val(*ptep) & _PAGE_INVALID) && - (pte_val(*ptep) & _PAGE_PROTECT)) { - pte_unmap_unlock(ptep, ptl); - /* - * We do not really care about unlocked. We will retry either - * way. But this allows fixup_user_fault to enable userfaultfd. - */ - if (fixup_user_fault(current, mm, addr, FAULT_FLAG_WRITE, - &unlocked)) { - up_read(&mm->mmap_sem); - return -EFAULT; - } - goto retry; - } new = old = pgste_get_lock(ptep); pgste_val(new) &= ~(PGSTE_GR_BIT | PGSTE_GC_BIT | -- 2.39.5