x86, xen: Disable highmem PTE allocation even when CONFIG_HIGHPTE=y (817a824b) · Commits · 戴 / test

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:

Ian 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: : 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:

H. Peter Anvin <hpa@zytor.com>

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

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