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[Xen-devel] [PATCH RFC v1 64/74] xen/pvshim: use default position for the m2p mappings

From: Roger Pau Monne <roger.pau@xxxxxxxxxx>

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

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>
 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 e152fe3a9e..f5a793b1d2 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;

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