[Xen-devel] [RFC PATCH 70/84] x86/smpboot: use xenheap pages for rpts in smpboot.

[<hongyax@xxxxxxxxxx>]

From: Hongyan Xia <hongyax@xxxxxxxxxx>

This is because a lot of code assumes that the rpt is in the direct map
region which is always mapped. Switching to domheap is non-trivial, so
use xenheap for now, which means a bit less security.

Signed-off-by: Hongyan Xia <hongyax@xxxxxxxxxx>
---
 xen/arch/x86/smpboot.c | 19 ++++++++++++-------
 1 file changed, 12 insertions(+), 7 deletions(-)

diff --git a/xen/arch/x86/smpboot.c b/xen/arch/x86/smpboot.c
index 53f9173f37..7034c699d6 100644
--- a/xen/arch/x86/smpboot.c
+++ b/xen/arch/x86/smpboot.c
@@ -832,14 +832,20 @@ static int setup_cpu_root_pgt(unsigned int cpu)
         goto out;
     }
 
-    rpt_mfn = alloc_xen_pagetable();
-    if ( mfn_eq(rpt_mfn, INVALID_MFN) )
+    /*
+     * Unfortunately, some code (especially in assembly) assumes the rpt is in
+     * the DIRECTMAP region and is always mapped. Making all of them adapt to
+     * the new page table APIs is non-trivial. For now, make it always mapped
+     * on the xenheap.
+     */
+    rpt = alloc_xenheap_page();
+    if ( !rpt )
     {
         rc = -ENOMEM;
         goto out;
     }
 
-    rpt = map_xen_pagetable(rpt_mfn);
+    rpt_mfn = _mfn(virt_to_mfn(rpt));
     clear_page(rpt);
     per_cpu(root_pgt_mfn, cpu) = rpt_mfn;
 
@@ -884,7 +890,6 @@ static int setup_cpu_root_pgt(unsigned int cpu)
         rc = clone_mapping((void *)per_cpu(stubs.addr, cpu), rpt);
 
  out:
-    UNMAP_XEN_PAGETABLE(rpt);
     return rc;
 }
 
@@ -900,7 +905,7 @@ static void cleanup_cpu_root_pgt(unsigned int cpu)
 
     per_cpu(root_pgt_mfn, cpu) = INVALID_MFN;
 
-    rpt = map_xen_pagetable(rpt_mfn);
+    rpt = mfn_to_virt(mfn_x(rpt_mfn));
 
     for ( r = root_table_offset(DIRECTMAP_VIRT_START);
           r < root_table_offset(HYPERVISOR_VIRT_END); ++r )
@@ -945,8 +950,8 @@ static void cleanup_cpu_root_pgt(unsigned int cpu)
         free_xen_pagetable(l3t_mfn);
     }
 
-    UNMAP_XEN_PAGETABLE(rpt);
-    free_xen_pagetable(rpt_mfn);
+    /* Unlike other levels, the root level is a xenheap page. */
+    free_xenheap_page(rpt);
 
     /* Also zap the stub mapping for this CPU. */
     if ( stub_linear )
-- 
2.17.1


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