x86/vsyscall/64: Use proper accessor to update P4D entry

Writing to it directly does not work for Xen PV guests.

Fixes: 49275fef986a ("x86/vsyscall/64: Explicitly set _PAGE_USER in the pagetable hierarchy")
Signed-off-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Juergen Gross <jgross@suse.com>
Acked-by: Andy Lutomirski <luto@kernel.org>
Cc: stable@vger.kernel.org
Link: https://lkml.kernel.org/r/20180319143154.3742-1-boris.ostrovsky@oracle.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>

diff --git a/arch/x86/entry/vsyscall/vsyscall_64.c b/arch/x86/entry/vsyscall/vsyscall_64.c
index 8560ef68a9d631163934a40415df65d2a495f2bc..317be365bce3a459b9d2b60dad6ad864868b1366 100644 (file)
--- a/arch/x86/entry/vsyscall/vsyscall_64.c
+++ b/arch/x86/entry/vsyscall/vsyscall_64.c
@@ -347,7 +347,7 @@ void __init set_vsyscall_pgtable_user_bits(pgd_t *root)
        set_pgd(pgd, __pgd(pgd_val(*pgd) | _PAGE_USER));
        p4d = p4d_offset(pgd, VSYSCALL_ADDR);
 #if CONFIG_PGTABLE_LEVELS >= 5
-       p4d->p4d |= _PAGE_USER;
+       set_p4d(p4d, __p4d(p4d_val(*p4d) | _PAGE_USER));
 #endif
        pud = pud_offset(p4d, VSYSCALL_ADDR);
        set_pud(pud, __pud(pud_val(*pud) | _PAGE_USER));