linux-kernel - [PATCH v2] x86: fix small LDT allocation for Xen

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Message-Id: <55E70BC2020000780009EF6C@prv-mh.provo.novell.com>
Date:	Wed, 02 Sep 2015 06:46:26 -0600
From:	"Jan Beulich" <JBeulich@...e.com>
To:	<mingo@...e.hu>, <tglx@...utronix.de>, <hpa@...or.com>
Cc:	"David Vrabel" <david.vrabel@...rix.com>, <luto@...nel.org>,
	"Boris Ostrovsky" <boris.ostrovsky@...cle.com>,
	"Konrad Rzeszutek Wilk" <konrad.wilk@...cle.com>,
	<linux-kernel@...r.kernel.org>
Subject: [PATCH v2] x86: fix small LDT allocation for Xen

While commit 37868fe113 ("x86/ldt: Make modify_ldt synchronous") added
a nice comment explaining that Xen needs page-aligned whole page chunks
for guest descriptor tables, it then nevertheless used kzalloc() on the
small size path. As I'm unaware of guarantees for kmalloc(PAGE_SIZE, )
to return page-aligned memory blocks, I believe this needs to be
switched back to __get_free_page().

Signed-off-by: Jan Beulich <jbeulich@...e.com>
Cc: Andy Lutomirski <luto@...nel.org>
Cc: Boris Ostrovsky <boris.ostrovsky@...cle.com>
Cc: David Vrabel <david.vrabel@...rix.com>
Cc: Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
---
v2: Also adjust the freeing side.
---
 arch/x86/kernel/ldt.c |    4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

--- 4.2/arch/x86/kernel/ldt.c
+++ 4.2-x86-LDT-alloc/arch/x86/kernel/ldt.c
@@ -58,7 +58,7 @@ static struct ldt_struct *alloc_ldt_stru
 	if (alloc_size > PAGE_SIZE)
 		new_ldt->entries = vzalloc(alloc_size);
 	else
-		new_ldt->entries = kzalloc(PAGE_SIZE, GFP_KERNEL);
+		new_ldt->entries = (void *)__get_free_page(GFP_KERNEL|__GFP_ZERO);
 
 	if (!new_ldt->entries) {
 		kfree(new_ldt);
@@ -95,7 +95,7 @@ static void free_ldt_struct(struct ldt_s
 	if (ldt->size * LDT_ENTRY_SIZE > PAGE_SIZE)
 		vfree(ldt->entries);
 	else
-		kfree(ldt->entries);
+		put_page(virt_to_page(ldt->entries));
 	kfree(ldt);
 }
 



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