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

[Jan Beulich]

>>> On 01.09.15 at 21:37, <luto@xxxxxxxxxxxxxx> wrote:
> On Tue, Sep 1, 2015 at 3:48 AM, Jan Beulich <JBeulich@xxxxxxxx> wrote:
>> 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@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>
>> ---
>>  arch/x86/kernel/ldt.c |    2 +-
>>  1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> --- 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);
> 
> This would need a corresponding change to the kfree path, right?

Oops - yes of course.

Jan

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