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    Subject[PATCH AUTOSEL 3.18 87/98] x86/ldt: Fix small LDT allocation for Xen
    Date
    From: Jan Beulich <JBeulich@suse.com>

    [ Upstream commit f454b478861325f067fd58ba7ee9f1b5c4a9d6a0 ]

    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>
    Signed-off-by: Sasha Levin <sashal@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 2bcc0525f1c1..6acc9dd91f36 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);
    }

    --
    2.17.1
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