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xen: ignore RW mapping of RO pages in pagetable_init

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When setting up the initial pagetable, which includes mappings of all
low physical memory, ignore a mapping which tries to set the RW bit on
an RO pte.  An RO pte indicates a page which is part of the current
pagetable, and so it cannot be allowed to become RW.

Once xen_pagetable_setup_done is called, set_pte reverts to its normal
behaviour.

Signed-off-by: Jeremy Fitzhardinge <jeremy@xensource.com>
Acked-by: Chris Wright <chrisw@sous-sol.org>
Cc: ebiederm@xmission.com (Eric W. Biederman)
This commit is contained in:
Jeremy Fitzhardinge 2007-07-17 18:37:05 -07:00 committed by Jeremy Fitzhardinge
parent f4f97b3ea9
commit 9a4029fd34
1 changed files with 25 additions and 2 deletions
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27
arch/i386/xen/enlighten.c
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@ -505,7 +505,7 @@ static void xen_write_cr3(unsigned long cr3)
/* Early in boot, while setting up the initial pagetable, assume
everything is pinned. */
static void xen_alloc_pt_init(struct mm_struct *mm, u32 pfn)
static __init void xen_alloc_pt_init(struct mm_struct *mm, u32 pfn)
{
BUG_ON(mem_map); /* should only be used early */
make_lowmem_page_readonly(__va(PFN_PHYS(pfn)));
@ -557,10 +557,32 @@ static void *xen_kmap_atomic_pte(struct page *page, enum km_type type)
}
#endif
static __init pte_t mask_rw_pte(pte_t *ptep, pte_t pte)
{
/* 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));
return pte;
}
/* Init-time set_pte while constructing initial pagetables, which
doesn't allow RO pagetable pages to be remapped RW */
static __init void xen_set_pte_init(pte_t *ptep, pte_t pte)
{
pte = mask_rw_pte(ptep, pte);
xen_set_pte(ptep, pte);
}
static __init void xen_pagetable_setup_start(pgd_t *base)
{
pgd_t *xen_pgd = (pgd_t *)xen_start_info->pt_base;
/* special set_pte for pagetable initialization */
paravirt_ops.set_pte = xen_set_pte_init;
init_mm.pgd = base;
/*
* copy top-level of Xen-supplied pagetable into place. For
@ -607,6 +629,7 @@ static __init void xen_pagetable_setup_done(pgd_t *base)
/* This will work as long as patching hasn't happened yet
(which it hasn't) */
paravirt_ops.alloc_pt = xen_alloc_pt;
paravirt_ops.set_pte = xen_set_pte;
if (!xen_feature(XENFEAT_auto_translated_physmap)) {
/*
@ -745,7 +768,7 @@ static const struct paravirt_ops xen_paravirt_ops __initdata = {
.kmap_atomic_pte = xen_kmap_atomic_pte,
#endif
.set_pte = xen_set_pte,
.set_pte = NULL, /* see xen_pagetable_setup_* */
.set_pte_at = xen_set_pte_at,
.set_pmd = xen_set_pmd,