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Commit 66a27dde authored by David Vrabel's avatar David Vrabel Committed by Konrad Rzeszutek Wilk
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xen/mm: zero PTEs for non-present MFNs in the initial page table 



When constructing the initial page tables, if the MFN for a usable PFN
is missing in the p2m then that frame is initially ballooned out.  In
this case, zero the PTE (as in decrease_reservation() in
drivers/xen/balloon.c).

This is obviously safe instead of having an valid PTE with an MFN of
INVALID_P2M_ENTRY (~0).

Signed-off-by: default avatarDavid Vrabel <david.vrabel@citrix.com>
Signed-off-by: default avatarKonrad Rzeszutek Wilk <konrad.wilk@oracle.com>
parent d095d43e

arch/x86/xen/mmu.c

+8 −1
Original line number Diff line number Diff line
@@ -1432,6 +1432,10 @@ static pte_t __init mask_rw_pte(pte_t *ptep, pte_t pte) 
 * Init-time set_pte while constructing initial pagetables, which

 * doesn't allow RO page table pages to be remapped RW.

 *

 * If there is no MFN for this PFN then this page is initially

 * ballooned out so clear the PTE (as in decrease_reservation() in

 * drivers/xen/balloon.c).

 *

 * Many of these PTE updates are done on unpinned and writable pages

 * and doing a hypercall for these is unnecessary and expensive.  At

 * this point it is not possible to tell if a page is pinned or not,
@@ -1440,7 +1444,10 @@ static pte_t __init mask_rw_pte(pte_t *ptep, pte_t pte) 
 */

static void __init xen_set_pte_init(pte_t *ptep, pte_t pte)

{

	if (pte_mfn(pte) != INVALID_P2M_ENTRY)

		pte = mask_rw_pte(ptep, pte);

	else

		pte = __pte_ma(0);



	native_set_pte(ptep, pte);

}