[Xen-changelog] [xen staging] xen/arm: mm: Set-up page permission for Xen mappings earlier on

[patchbot@xxxxxxx]

commit 00c96d77422a4b84247bec5dadf434363d312cac
Author:     Julien Grall <julien.grall@xxxxxxx>
AuthorDate: Thu Nov 29 11:37:43 2018 +0000
Commit:     Stefano Stabellini <sstabellini@xxxxxxxxxx>
CommitDate: Wed Dec 12 15:07:32 2018 -0800

    xen/arm: mm: Set-up page permission for Xen mappings earlier on
    
    Xen mapping is first create using a 2MB page and then shatterred in 4KB
    page for fine-graine permission. However, it is not safe to break-down
    superpage page without going to an intermediate step invalidating
    the entry.
    
    As we are changing Xen mappings, we cannot go through the intermediate
    step. The only solution is to create Xen mapping using 4KB entries
    directly. As the Xen should always access the mappings according with
    the runtime permission, it is then possible to set-up the permissions
    while create the mapping.
    
    We are still playing with the fire as there are still some
    break-before-make issue in setup_pagetables (i.e switch between 2 sets of
    page-tables). But it should slightly be better than the current state.
    
    Signed-off-by: Julien Grall <julien.grall@xxxxxxx>
    Reported-by: Shameerali Kolothum Thodi 
<shameerali.kolothum.thodi@xxxxxxxxxx>
    Reported-by: Jan-Peter Larsson <Jan-Peter.Larsson@xxxxxxx>
    Reviewed-by: Stefano Stabellini <sstabellini@xxxxxxxxxx>
    Tested-by: Shameer Kolothum <shameerali.kolothum.thodi@xxxxxxxxxx>
    Tested-by: Matthew Daley <mattd@xxxxxxxxxxx>
---
 xen/arch/arm/mm.c | 49 ++++++++++++++++++++++---------------------------
 1 file changed, 22 insertions(+), 27 deletions(-)

diff --git a/xen/arch/arm/mm.c b/xen/arch/arm/mm.c
index 987fcb9162..2556e57a99 100644
--- a/xen/arch/arm/mm.c
+++ b/xen/arch/arm/mm.c
@@ -649,11 +649,31 @@ void __init setup_pagetables(unsigned long 
boot_phys_offset, paddr_t xen_paddr)
     }
 #endif
 
+    /* Break up the Xen mapping into 4k pages and protect them separately. */
+    for ( i = 0; i < LPAE_ENTRIES; i++ )
+    {
+        mfn_t mfn = mfn_add(maddr_to_mfn(xen_paddr), i);
+        unsigned long va = XEN_VIRT_START + (i << PAGE_SHIFT);
+
+        if ( !is_kernel(va) )
+            break;
+        pte = mfn_to_xen_entry(mfn, MT_NORMAL);
+        pte.pt.table = 1; /* 4k mappings always have this bit set */
+        if ( is_kernel_text(va) || is_kernel_inittext(va) )
+        {
+            pte.pt.xn = 0;
+            pte.pt.ro = 1;
+        }
+        if ( is_kernel_rodata(va) )
+            pte.pt.ro = 1;
+        xen_xenmap[i] = pte;
+    }
+
     /* Initialise xen second level entries ... */
     /* ... Xen's text etc */
 
-    pte = mfn_to_xen_entry(maddr_to_mfn(xen_paddr), MT_NORMAL);
-    pte.pt.xn = 0;/* Contains our text mapping! */
+    pte = pte_of_xenaddr((vaddr_t)xen_xenmap);
+    pte.pt.table = 1;
     xen_second[second_table_offset(XEN_VIRT_START)] = pte;
 
     /* ... Fixmap */
@@ -693,31 +713,6 @@ void __init setup_pagetables(unsigned long 
boot_phys_offset, paddr_t xen_paddr)
     clear_table(boot_second);
     clear_table(boot_third);
 
-    /* Break up the Xen mapping into 4k pages and protect them separately. */
-    for ( i = 0; i < LPAE_ENTRIES; i++ )
-    {
-        mfn_t mfn = mfn_add(maddr_to_mfn(xen_paddr), i);
-        unsigned long va = XEN_VIRT_START + (i << PAGE_SHIFT);
-        if ( !is_kernel(va) )
-            break;
-        pte = mfn_to_xen_entry(mfn, MT_NORMAL);
-        pte.pt.table = 1; /* 4k mappings always have this bit set */
-        if ( is_kernel_text(va) || is_kernel_inittext(va) )
-        {
-            pte.pt.xn = 0;
-            pte.pt.ro = 1;
-        }
-        if ( is_kernel_rodata(va) )
-            pte.pt.ro = 1;
-        write_pte(xen_xenmap + i, pte);
-        /* No flush required here as page table is not hooked in yet. */
-    }
-
-    pte = pte_of_xenaddr((vaddr_t)xen_xenmap);
-    pte.pt.table = 1;
-    write_pte(xen_second + second_linear_offset(XEN_VIRT_START), pte);
-    /* TLBFLUSH and ISB would be needed here, but wait until we set WXN */
-
     /* From now on, no mapping may be both writable and executable. */
     WRITE_SYSREG32(READ_SYSREG32(SCTLR_EL2) | SCTLR_WXN, SCTLR_EL2);
     /* Flush everything after setting WXN bit. */
--
generated by git-patchbot for /home/xen/git/xen.git#staging

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