linux-kernel - [tip:x86/asm] x86/xen: Simplify set_aliased

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Message-ID: <tip-99158f10e91768d34c5004c40c42f802b719bcae@git.kernel.org>
Date:	Sat, 11 Jun 2016 02:34:10 -0700
From:	tip-bot for Andy Lutomirski <tipbot@...or.com>
To:	linux-tip-commits@...r.kernel.org
Cc:	xen-devel@...ts.xen.org, bp@...en8.de, boris.ostrovsky@...cle.com,
	keescook@...omium.org, luto@...nel.org, mingo@...nel.org,
	david.vrabel@...rix.com, hpa@...or.com,
	torvalds@...ux-foundation.org, luto@...capital.net,
	tglx@...utronix.de, peterz@...radead.org,
	linux-kernel@...r.kernel.org, brgerst@...il.com,
	konrad.wilk@...cle.com, jbeulich@...e.com,
	andrew.cooper3@...rix.com, dvrabel@...tab.net, dvlasenk@...hat.com
Subject: [tip:x86/asm] x86/xen: Simplify set_aliased_prot()

Commit-ID:  99158f10e91768d34c5004c40c42f802b719bcae
Gitweb:     http://git.kernel.org/tip/99158f10e91768d34c5004c40c42f802b719bcae
Author:     Andy Lutomirski <luto@...nel.org>
AuthorDate: Tue, 24 May 2016 15:48:38 -0700
Committer:  Ingo Molnar <mingo@...nel.org>
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@...nel.org>
Reviewed-by: Andrew Cooper <andrew.cooper3@...rix.com>
Acked-by: David Vrabel <david.vrabel@...rix.com>
Cc: Andy Lutomirski <luto@...capital.net>
Cc: Boris Ostrovsky <boris.ostrovsky@...cle.com>
Cc: Borislav Petkov <bp@...en8.de>
Cc: Brian Gerst <brgerst@...il.com>
Cc: David Vrabel <dvrabel@...tab.net>
Cc: Denys Vlasenko <dvlasenk@...hat.com>
Cc: H. Peter Anvin <hpa@...or.com>
Cc: Jan Beulich <jbeulich@...e.com>
Cc: Kees Cook <keescook@...omium.org>
Cc: Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: xen-devel <xen-devel@...ts.xen.org>
Link: http://lkml.kernel.org/r/0706f1a2538e481194514197298cca6b5e3f2638.1464129798.git.luto@kernel.org
Signed-off-by: Ingo Molnar <mingo@...nel.org>
---
 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();