Commit 9a4029fd authored by Jeremy Fitzhardinge's avatar Jeremy Fitzhardinge Committed by Jeremy Fitzhardinge
Browse files

xen: ignore RW mapping of RO pages in pagetable_init 



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: default avatarJeremy Fitzhardinge <jeremy@xensource.com>
Acked-by: default avatarChris Wright <chrisw@sous-sol.org>
Cc: ebiederm@xmission.com (Eric W. Biederman)
parent f4f97b3e

arch/i386/xen/enlighten.c

+25 −2
Original line number Diff line number Diff line
@@ -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,

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