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@arm.com>
Reported-by: Shameerali Kolothum Thodi <shameerali.kolothum.thodi@huawei.com>
Reported-by: Jan-Peter Larsson <Jan-Peter.Larsson@arm.com>
Reviewed-by: Stefano Stabellini <sstabellini@kernel.org>
Tested-by: Shameer Kolothum <shameerali.kolothum.thodi@huawei.com>
Tested-by: Matthew Daley <mattd@bugfuzz.com>
(cherry picked from commit 00c96d77422a4b84247bec5dadf434363d312cac)

diff --git a/xen/arch/arm/mm.c b/xen/arch/arm/mm.c
index a6de77c28c2199310ebd24ca498a2b4bab39c5df..bdf427ca645f90183480ca5d97b4b85d6499fcf9 100644 (file)
--- 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. */