[tip:x86/asm] x86/xen: Simplify set_aliased_prot()

[tip-bot for Andy Lutomirski]

Commit-ID:  99158f10e91768d34c5004c40c42f802b719bcae
Gitweb:     http://git.kernel.org/tip/99158f10e91768d34c5004c40c42f802b719bcae
Author:     Andy Lutomirski <luto@xxxxxxxxxx>
AuthorDate: Tue, 24 May 2016 15:48:38 -0700
Committer:  Ingo Molnar <mingo@xxxxxxxxxx>
CommitDate: Sat, 11 Jun 2016 11:28:11 +0200

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@xxxxxxxxxx>
Reviewed-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
Acked-by: David Vrabel <david.vrabel@xxxxxxxxxx>
Cc: Andy Lutomirski <luto@xxxxxxxxxxxxxx>
Cc: Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>
Cc: Borislav Petkov <bp@xxxxxxxxx>
Cc: Brian Gerst <brgerst@xxxxxxxxx>
Cc: David Vrabel <dvrabel@xxxxxxxxxx>
Cc: Denys Vlasenko <dvlasenk@xxxxxxxxxx>
Cc: H. Peter Anvin <hpa@xxxxxxxxx>
Cc: Jan Beulich <jbeulich@xxxxxxxx>
Cc: Kees Cook <keescook@xxxxxxxxxxxx>
Cc: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: xen-devel <xen-devel@xxxxxxxxxxxxx>
Link: http://lkml.kernel.org/r/0706f1a2538e481194514197298cca6b5e3f2638.1464129798.git.luto@xxxxxxxxxx
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
---
 arch/x86/xen/enlighten.c | 4 +---
 1 file changed, 1 insertion(+), 3 deletions(-)

diff --git a/arch/x86/xen/enlighten.c b/arch/x86/xen/enlighten.c
index 760789a..0f87db2 100644
--- a/arch/x86/xen/enlighten.c
+++ b/arch/x86/xen/enlighten.c
@@ -521,9 +521,7 @@ 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();