xen: Cope with unmapped pages when initializing kernel pagetable

Xen requires that all pages containing pagetable entries to be mapped
read-only.  If pages used for the initial pagetable are already mapped
then we can change the mapping to RO.  However, if they are initially
unmapped, we need to make sure that when they are later mapped, they
are also mapped RO.

We do this by knowing that the kernel pagetable memory is pre-allocated
in the range e820_table_start - e820_table_end, so any pfn within this
range should be mapped read-only.  However, the pagetable setup code
early_ioremaps the pages to write their entries, so we must make sure
that mappings created in the early_ioremap fixmap area are mapped RW.
(Those mappings are removed before the pages are presented to Xen
as pagetable pages.)

Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>
LKML-Reference: <4CB63A80.8060702@goop.org>
Cc: Yinghai Lu <yinghai@kernel.org>
Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>

1 files changed, 5 insertions, 0 deletions

diff --git a/arch/x86/mm/ioremap.c b/arch/x86/mm/ioremap.c
index 3ba6e0608c55..0369843511dc 100644
--- a/arch/x86/mm/ioremap.c
+++ b/arch/x86/mm/ioremap.c
@@ -362,6 +362,11 @@ static inline pte_t * __init early_ioremap_pte(unsigned long addr)
 	return &bm_pte[pte_index(addr)];
 }
 
+bool __init is_early_ioremap_ptep(pte_t *ptep)
+{
+	return ptep >= &bm_pte[0] && ptep < &bm_pte[PAGE_SIZE/sizeof(pte_t)];
+}
+
 static unsigned long slot_virt[FIX_BTMAPS_SLOTS] __initdata;
 
 void __init early_ioremap_init(void)