[Xen-changelog] [xen stable-4.12] x86/mm: correctly initialise M2P entries on boot

[patchbot@xxxxxxx]

commit 04a2fe9c507d7f15190378574ced071888ff4b7b
Author:     Igor Druzhinin <igor.druzhinin@xxxxxxxxxx>
AuthorDate: Mon Sep 23 14:23:27 2019 +0200
Commit:     Jan Beulich <jbeulich@xxxxxxxx>
CommitDate: Mon Sep 23 14:23:27 2019 +0200

    x86/mm: correctly initialise M2P entries on boot
    
    Since guest resource management work it's now possible to have a page
    assigned to a domain without a valid M2P entry. Some paths in the code
    rely on the fact a GFN returned from mfn_to_gfn() for such a page
    is not valid as well, i.e. see arch_iommu_populate_page_table().
    
    For systems without 512GB contiguous RAM M2P entries were already
    correctly initialised on boot with INVALID_M2P_ENTRY (~0UL) but
    on systems where M2P could be covered by a single 1GB page directory
    0x77 poison was used instead. That eventually resulted in a crash
    during IOMMU construction on systems without shared PTs enabled.
    
    While here fix up compat M2P entries as well.
    
    Signed-off-by: Igor Druzhinin <igor.druzhinin@xxxxxxxxxx>
    Reviewed-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
    master commit: 6c093931a765803cfc7b0df466ee032760cc8020
    master date: 2019-08-27 13:40:42 +0100
---
 xen/arch/x86/x86_64/mm.c | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/xen/arch/x86/x86_64/mm.c b/xen/arch/x86/x86_64/mm.c
index 899b883b2d..cda9fbba00 100644
--- a/xen/arch/x86/x86_64/mm.c
+++ b/xen/arch/x86/x86_64/mm.c
@@ -574,8 +574,9 @@ void __init paging_init(void)
                     page_to_mfn(l1_pg),
                     1UL << (2 * PAGETABLE_ORDER),
                     PAGE_HYPERVISOR);
+                /* Fill with INVALID_M2P_ENTRY. */
                 memset((void *)(RDWR_MPT_VIRT_START + (i << 
L2_PAGETABLE_SHIFT)),
-                       0x77, 1UL << L3_PAGETABLE_SHIFT);
+                       0xFF, 1UL << L3_PAGETABLE_SHIFT);
 
                 ASSERT(!l2_table_offset(va));
                 /* NB. Cannot be GLOBAL: guest user mode should not see it. */
@@ -666,10 +667,10 @@ void __init paging_init(void)
             page_to_mfn(l1_pg),
             1UL << PAGETABLE_ORDER,
             PAGE_HYPERVISOR);
+        /* Fill with INVALID_M2P_ENTRY. */
         memset((void *)(RDWR_COMPAT_MPT_VIRT_START +
                         (i << L2_PAGETABLE_SHIFT)),
-               0x55,
-               1UL << L2_PAGETABLE_SHIFT);
+               0xFF, 1UL << L2_PAGETABLE_SHIFT);
         /* NB. Cannot be GLOBAL as the ptes get copied into per-VM space. */
         l2e_write(l2_ro_mpt, l2e_from_page(l1_pg, _PAGE_PSE|_PAGE_PRESENT));
     }
--
generated by git-patchbot for /home/xen/git/xen.git#stable-4.12

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