[Xen-changelog] [xen stable-4.10] xen/pvshim: use default position for the m2p mappings

[patchbot@xxxxxxx]

commit b5be9c817d04b006886a0d7b87eacf7bd78f504d
Author:     Roger Pau Monne <roger.pau@xxxxxxxxxx>
AuthorDate: Thu Jan 11 11:41:20 2018 +0000
Commit:     Roger Pau Monne <roger.pau@xxxxxxxxxx>
CommitDate: Fri Jan 12 15:47:32 2018 +0000

    xen/pvshim: use default position for the m2p mappings
    
    When running a 32bit kernel as Dom0 on a 64bit hypervisor the
    hypervisor will try to shrink the hypervisor hole to the minimum
    needed, and thus requires the Dom0 to use XENMEM_machphys_mapping in
    order to fetch the position of the start of the hypervisor virtual
    mappings.
    
    Disable this feature when running as a PV shim, since some DomU
    kernels don't implemented XENMEM_machphys_mapping and break if the m2p
    doesn't begin at the default address.
    
    NB: support for the XENMEM_machphys_mapping was added in Linux by
    commit 7e7750.
    
    Signed-off-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>
    Acked-by: Jan Beulich <jbeulich@xxxxxxxx>
---
 xen/arch/x86/pv/dom0_build.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/xen/arch/x86/pv/dom0_build.c b/xen/arch/x86/pv/dom0_build.c
index 72752b8656..ebcb47bf26 100644
--- a/xen/arch/x86/pv/dom0_build.c
+++ b/xen/arch/x86/pv/dom0_build.c
@@ -398,7 +398,8 @@ int __init dom0_construct_pv(struct domain *d,
     if ( parms.pae == XEN_PAE_EXTCR3 )
             set_bit(VMASST_TYPE_pae_extended_cr3, &d->vm_assist);
 
-    if ( (parms.virt_hv_start_low != UNSET_ADDR) && elf_32bit(&elf) )
+    if ( !pv_shim && (parms.virt_hv_start_low != UNSET_ADDR) &&
+         elf_32bit(&elf) )
     {
         unsigned long mask = (1UL << L2_PAGETABLE_SHIFT) - 1;
         value = (parms.virt_hv_start_low + mask) & ~mask;
--
generated by git-patchbot for /home/xen/git/xen.git#stable-4.10

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