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Commit 817a824b authored by Ian Campbell's avatar Ian Campbell Committed by H. Peter Anvin
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x86, xen: Disable highmem PTE allocation even when CONFIG_HIGHPTE=y 



There's a path in the pagefault code where the kernel deliberately
breaks its own locking rules by kmapping a high pte page without
holding the pagetable lock (in at least page_check_address). This
breaks Xen's ability to track the pinned/unpinned state of the
page. There does not appear to be a viable workaround for this
behaviour so simply disable HIGHPTE for all Xen guests.

Signed-off-by: default avatarIan Campbell <ian.campbell@citrix.com>
LKML-Reference: <1267204562-11844-1-git-send-email-ian.campbell@citrix.com>
Cc: Jeremy Fitzhardinge <jeremy@goop.org>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Pasi Kärkkäinen <pasik@iki.fi>
Cc: <stable@kernel.org> # .32.x: 14315592: Allow highmem user page tables to be disabled at boot time
Cc: <stable@kernel.org> # .32.x
Cc: <xen-devel@lists.xensource.com>
Signed-off-by: default avatarH. Peter Anvin <hpa@zytor.com>
parent c1fd1b43

arch/x86/xen/enlighten.c

+7 −0
Original line number Diff line number Diff line
@@ -50,6 +50,7 @@ 
#include <asm/traps.h>

#include <asm/setup.h>

#include <asm/desc.h>

#include <asm/pgalloc.h>

#include <asm/pgtable.h>

#include <asm/tlbflush.h>

#include <asm/reboot.h>
@@ -1094,6 +1095,12 @@ asmlinkage void __init xen_start_kernel(void) 


	__supported_pte_mask |= _PAGE_IOMAP;



	/*

	 * Prevent page tables from being allocated in highmem, even

	 * if CONFIG_HIGHPTE is enabled.

	 */

	__userpte_alloc_gfp &= ~__GFP_HIGHMEM;



	/* Work out if we support NX */

	x86_configure_nx();

arch/x86/xen/mmu.c

+6 −5
Original line number Diff line number Diff line
@@ -1432,14 +1432,15 @@ static void *xen_kmap_atomic_pte(struct page *page, enum km_type type) 
{

	pgprot_t prot = PAGE_KERNEL;



	/*

	 * We disable highmem allocations for page tables so we should never

	 * see any calls to kmap_atomic_pte on a highmem page.

	 */

	BUG_ON(PageHighMem(page));



	if (PagePinned(page))

		prot = PAGE_KERNEL_RO;



	if (0 && PageHighMem(page))

		printk("mapping highpte %lx type %d prot %s\n",

		       page_to_pfn(page), type,

		       (unsigned long)pgprot_val(prot) & _PAGE_RW ? "WRITE" : "READ");



	return kmap_atomic_prot(page, type, prot);

}

#endif