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>
diff --git a/arch/x86/xen/mmu.c b/arch/x86/xen/mmu.c
index 4fe04ac..7d55e9e 100644
--- a/arch/x86/xen/mmu.c
+++ b/arch/x86/xen/mmu.c
@@ -56,6 +56,7 @@
#include <asm/e820.h>
#include <asm/linkage.h>
#include <asm/page.h>
+#include <asm/init.h>
#include <asm/xen/hypercall.h>
#include <asm/xen/hypervisor.h>
@@ -360,7 +361,8 @@
unsigned int level;
pte = lookup_address(address, &level);
- BUG_ON(pte == NULL);
+ if (pte == NULL)
+ return; /* vaddr missing */
ptev = pte_wrprotect(*pte);
@@ -375,7 +377,8 @@
unsigned int level;
pte = lookup_address(address, &level);
- BUG_ON(pte == NULL);
+ if (pte == NULL)
+ return; /* vaddr missing */
ptev = pte_mkwrite(*pte);
@@ -1509,13 +1512,25 @@
#endif
}
-#ifdef CONFIG_X86_32
static __init pte_t mask_rw_pte(pte_t *ptep, pte_t pte)
{
+ unsigned long pfn = pte_pfn(pte);
+
+#ifdef CONFIG_X86_32
/* If there's an existing pte, then don't allow _PAGE_RW to be set */
if (pte_val_ma(*ptep) & _PAGE_PRESENT)
pte = __pte_ma(((pte_val_ma(*ptep) & _PAGE_RW) | ~_PAGE_RW) &
pte_val_ma(pte));
+#endif
+
+ /*
+ * If the new pfn is within the range of the newly allocated
+ * kernel pagetable, and it isn't being mapped into an
+ * early_ioremap fixmap slot, make sure it is RO.
+ */
+ if (!is_early_ioremap_ptep(ptep) &&
+ pfn >= e820_table_start && pfn < e820_table_end)
+ pte = pte_wrprotect(pte);
return pte;
}
@@ -1528,7 +1543,6 @@
xen_set_pte(ptep, pte);
}
-#endif
static void pin_pagetable_pfn(unsigned cmd, unsigned long pfn)
{
@@ -1973,11 +1987,7 @@
.alloc_pmd_clone = paravirt_nop,
.release_pmd = xen_release_pmd_init,
-#ifdef CONFIG_X86_64
- .set_pte = xen_set_pte,
-#else
.set_pte = xen_set_pte_init,
-#endif
.set_pte_at = xen_set_pte_at,
.set_pmd = xen_set_pmd_hyper,