[PATCH v3] x86: fix small LDT allocation for Xen

[PATCH v3] x86: fix small LDT allocation for Xen

[Jan Beulich]

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() (or better get_zeroed_page()).

Signed-off-by: Jan Beulich <jbeulich@suse.com>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Cc: David Vrabel <david.vrabel@citrix.com>
Cc: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
---
v3: Use get_zeroed_page() and free_page() respectively.
---
 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_zeroed_page(GFP_KERNEL);
 
 	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);
+		free_page((unsigned long)ldt->entries);
 	kfree(ldt);
 }
 

[tip:x86/urgent] x86/ldt: Fix small LDT allocation for Xen

[tip-bot for Jan Beulich]

Commit-ID:  f454b478861325f067fd58ba7ee9f1b5c4a9d6a0
Gitweb:     http://git.kernel.org/tip/f454b478861325f067fd58ba7ee9f1b5c4a9d6a0
Author:     Jan Beulich <JBeulich@suse.com>
AuthorDate: Wed, 2 Sep 2015 09:45:58 -0600
Committer:  Ingo Molnar <mingo@kernel.org>
CommitDate: Mon, 14 Sep 2015 12:10:50 +0200

x86/ldt: Fix small LDT allocation for Xen

While the following 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() (or better get_zeroed_page()).

Signed-off-by: Jan Beulich <jbeulich@suse.com>
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: David Vrabel <david.vrabel@citrix.com>
Cc: Denys Vlasenko <dvlasenk@redhat.com>
Cc: H. Peter Anvin <hpa@zytor.com>
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>
Link: http://lkml.kernel.org/r/55E735D6020000780009F1E6@prv-mh.provo.novell.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
---
 arch/x86/kernel/ldt.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kernel/ldt.c b/arch/x86/kernel/ldt.c
index 2bcc052..6acc9dd 100644
--- a/arch/x86/kernel/ldt.c
+++ b/arch/x86/kernel/ldt.c
@@ -58,7 +58,7 @@ static struct ldt_struct *alloc_ldt_struct(int size)
 	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_zeroed_page(GFP_KERNEL);
 
 	if (!new_ldt->entries) {
 		kfree(new_ldt);
@@ -95,7 +95,7 @@ static void free_ldt_struct(struct ldt_struct *ldt)
 	if (ldt->size * LDT_ENTRY_SIZE > PAGE_SIZE)
 		vfree(ldt->entries);
 	else
-		kfree(ldt->entries);
+		free_page((unsigned long)ldt->entries);
 	kfree(ldt);
 }