[lkml]   [2009]   [Feb]   [27]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
Messages in this thread
Patch in this message
Subject[PATCH] xen: clear reserved bits in l3 entries given in the initial pagetables
From: Ian Campbell <>

In native PAE, the only flag that may be legitimately set in an L3
entry is Present. When Xen grafts the top-level PAE L3 pagetable
entries into the L4 pagetable, it must also set the other permissions
flags so that the mapped pages are actually accessible.

However, due to a bug in the hypervisor, it validates update to the L3
entries as formal PAE entries, so it will refuse to validate these
entries with the extra bits requires for 4-level pagetables.

This patch simply masks the entries back to the bare PAE level,
leaving Xen to add whatever bits it feels are necessary.

Signed-off-by: Ian Campbell <>
Signed-off-by: Jeremy Fitzhardinge <>
arch/x86/xen/mmu.c | 15 +++++++++++++++
1 files changed, 15 insertions(+), 0 deletions(-)

diff --git a/arch/x86/xen/mmu.c b/arch/x86/xen/mmu.c
index 367a7d2..5f034a1 100644
--- a/arch/x86/xen/mmu.c
+++ b/arch/x86/xen/mmu.c
@@ -1778,6 +1778,7 @@ __init pgd_t *xen_setup_kernel_pagetable(pgd_t *pgd,
unsigned long max_pfn)
pmd_t *kernel_pmd;
+ int i;

init_pg_tables_start = __pa(pgd);
init_pg_tables_end = __pa(pgd) + xen_start_info->nr_pt_frames*PAGE_SIZE;
@@ -1789,6 +1790,20 @@ __init pgd_t *xen_setup_kernel_pagetable(pgd_t *pgd,
xen_map_identity_early(level2_kernel_pgt, max_pfn);

memcpy(swapper_pg_dir, pgd, sizeof(pgd_t) * PTRS_PER_PGD);
+ /*
+ * When running a 32 bit domain 0 on a 64 bit hypervisor a
+ * pinned L3 (such as the initial pgd here) contains bits
+ * which are reserved in the PAE layout but not in the 64 bit
+ * layout. Unfortunately some versions of the hypervisor
+ * (incorrectly) validate compat mode guests against the PAE
+ * layout and hence will not allow such a pagetable to be
+ * pinned by the guest. Therefore we mask off only the PFN and
+ * Present bits of the supplied L3.
+ */
+ for (i = 0; i < PTRS_PER_PGD; i++)
+ swapper_pg_dir[i].pgd &= (PTE_PFN_MASK | _PAGE_PRESENT);
__pgd(__pa(level2_kernel_pgt) | _PAGE_PRESENT));


 \ /
  Last update: 2009-02-28 03:07    [W:0.160 / U:0.576 seconds]
©2003-2018 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site