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

From: Jan Beulich
Date: Wed Sep 02 2015 - 11:46:06 EST

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@xxxxxxxx>
Cc: Andy Lutomirski <luto@xxxxxxxxxx>
Cc: Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>
Cc: David Vrabel <david.vrabel@xxxxxxxxxx>
Cc: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>
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);
- new_ldt->entries = kzalloc(PAGE_SIZE, GFP_KERNEL);
+ new_ldt->entries = (void *)get_zeroed_page(GFP_KERNEL);

if (!new_ldt->entries) {
@@ -95,7 +95,7 @@ static void free_ldt_struct(struct ldt_s
if (ldt->size * LDT_ENTRY_SIZE > PAGE_SIZE)
- kfree(ldt->entries);
+ free_page((unsigned long)ldt->entries);

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