x86/xen: Simplify set_aliased_prot()

A year ago, via the following commit:

  aa1acff356bb ("x86/xen: Probe target addresses in set_aliased_prot() before the hypercall")

I added an explicit probe to work around a hypercall issue.  The code can
be simplified by using probe_kernel_read().

No change in functionality.

Signed-off-by: Andy Lutomirski <luto@kernel.org>
Reviewed-by: Andrew Cooper <andrew.cooper3@citrix.com>
Acked-by: David Vrabel <david.vrabel@citrix.com>
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: David Vrabel <dvrabel@cantab.net>
Cc: Denys Vlasenko <dvlasenk@redhat.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Jan Beulich <jbeulich@suse.com>
Cc: Kees Cook <keescook@chromium.org>
Cc: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: xen-devel <xen-devel@lists.xen.org>
Link: http://lkml.kernel.org/r/0706f1a2538e481194514197298cca6b5e3f2638.1464129798.git.luto@kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
(cherry picked from commit 99158f10e91768d34c5004c40c42f802b719bcae)
Signed-off-by: Bob Liu <bob.liu@oracle.com>
Orabug: 24820937

diff --git a/arch/x86/xen/enlighten.c b/arch/x86/xen/enlighten.c
index ecd13e97f4f4e97ccdc7608ac37fe6d6560e00c7..8015db319bd7b15c9c9f36b2a2b65dae1b0ab42a 100644 (file)
--- a/arch/x86/xen/enlighten.c
+++ b/arch/x86/xen/enlighten.c
@@ -553,9 +553,7 @@ static void set_aliased_prot(void *v, pgprot_t prot)
 
        preempt_disable();
 
-       pagefault_disable();    /* Avoid warnings due to being atomic. */
-       __get_user(dummy, (unsigned char __user __force *)v);
-       pagefault_enable();
+       probe_kernel_read(&dummy, v, 1);
 
        if (HYPERVISOR_update_va_mapping((unsigned long)v, pte, 0))
                BUG();