[Xen-devel] [PATCH] xen/x86: Remap text/data/bss with appropriate permissions

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

c/s cf39362 "x86: use 2M superpages for text/data/bss mappings" served two
purposes; to map the primary code and data with appropriate pagetable
permissions (rather than unilaterally RWX), and to reduce the TLB pressure.

The extra alignment exposed a SYSLinux issue, and was partly reverted by c/s
0b8a172 "x86: partially revert use of 2M mappings for hypervisor image".

This change reinstates the pagetable permission improvements while avoiding
the 2M alignment issue.

Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
---
CC: Jan Beulich <JBeulich@xxxxxxxx>
---
 xen/arch/x86/setup.c   | 24 ++++++++++++++++++++++++
 xen/arch/x86/xen.lds.S | 16 ++++++++++++++++
 2 files changed, 40 insertions(+)

diff --git a/xen/arch/x86/setup.c b/xen/arch/x86/setup.c
index c5c332d..e278a7b 100644
--- a/xen/arch/x86/setup.c
+++ b/xen/arch/x86/setup.c
@@ -529,9 +529,33 @@ static void noinline init_done(void)
     }
     else
     {
+        /* Mark .text as RX (avoiding the first 2M superpage). */
+        map_pages_to_xen(XEN_VIRT_START + MB(2),
+                         PFN_DOWN(__pa(XEN_VIRT_START + MB(2))),
+                         PFN_DOWN(__2M_text_end -
+                                  (const char *)(XEN_VIRT_START + MB(2))),
+                         PAGE_HYPERVISOR_RX);
+
+        /* Mark .rodata as RO. */
+        map_pages_to_xen((unsigned long)&__2M_rodata_start,
+                         PFN_DOWN(__pa(__2M_rodata_start)),
+                         PFN_DOWN(__2M_rodata_end - __2M_rodata_start),
+                         PAGE_HYPERVISOR_RO);
+
+        /* Free and reuse .init. */
         destroy_xen_mappings((unsigned long)&__init_begin,
                              (unsigned long)&__init_end);
         init_xenheap_pages(__pa(__init_begin), __pa(__init_end));
+
+        /* Mark .data and .bss as RW. */
+        map_pages_to_xen((unsigned long)&__2M_rwdata_start,
+                         PFN_DOWN(__pa(__2M_rwdata_start)),
+                         PFN_DOWN(__2M_rwdata_end - __2M_rwdata_start),
+                         PAGE_HYPERVISOR_RW);
+
+        /* Drop the remaining mappings in the shattered superpage. */
+        destroy_xen_mappings((unsigned long)&__2M_rwdata_end,
+                             ROUNDUP((unsigned long)&__2M_rwdata_end, MB(2)));
     }
 
     printk("Freed %ldkB init memory.\n", (long)(__init_end-__init_begin)>>10);
diff --git a/xen/arch/x86/xen.lds.S b/xen/arch/x86/xen.lds.S
index 961f48f..ab8ba74 100644
--- a/xen/arch/x86/xen.lds.S
+++ b/xen/arch/x86/xen.lds.S
@@ -55,6 +55,8 @@ SECTIONS
 
 #ifdef EFI
   . = ALIGN(MB(2));
+#else
+  . = ALIGN(PAGE_SIZE);
 #endif
   __2M_text_end = .;
 
@@ -98,6 +100,8 @@ SECTIONS
 
 #ifdef EFI
   . = ALIGN(MB(2));
+#else
+  . = ALIGN(PAGE_SIZE);
 #endif
   __2M_rodata_end = .;
 
@@ -167,6 +171,8 @@ SECTIONS
 
 #ifdef EFI
   . = ALIGN(MB(2));
+#else
+  . = ALIGN(PAGE_SIZE);
 #endif
   __2M_init_end = .;
 
@@ -211,6 +217,8 @@ SECTIONS
 
 #ifdef EFI
   . = ALIGN(MB(2));
+#else
+  . = ALIGN(PAGE_SIZE);
 #endif
   __2M_rwdata_end = .;
 
@@ -269,6 +277,14 @@ ASSERT(IS_ALIGNED(__2M_init_start,   MB(2)), 
"__2M_init_start misaligned")
 ASSERT(IS_ALIGNED(__2M_init_end,     MB(2)), "__2M_init_end misaligned")
 ASSERT(IS_ALIGNED(__2M_rwdata_start, MB(2)), "__2M_rwdata_start misaligned")
 ASSERT(IS_ALIGNED(__2M_rwdata_end,   MB(2)), "__2M_rwdata_end misaligned")
+#else
+ASSERT(IS_ALIGNED(__2M_text_end,     PAGE_SIZE), "__2M_text_end misaligned")
+ASSERT(IS_ALIGNED(__2M_rodata_start, PAGE_SIZE), "__2M_rodata_start 
misaligned")
+ASSERT(IS_ALIGNED(__2M_rodata_end,   PAGE_SIZE), "__2M_rodata_end misaligned")
+ASSERT(IS_ALIGNED(__2M_init_start,   PAGE_SIZE), "__2M_init_start misaligned")
+ASSERT(IS_ALIGNED(__2M_init_end,     PAGE_SIZE), "__2M_init_end misaligned")
+ASSERT(IS_ALIGNED(__2M_rwdata_start, PAGE_SIZE), "__2M_rwdata_start 
misaligned")
+ASSERT(IS_ALIGNED(__2M_rwdata_end,   PAGE_SIZE), "__2M_rwdata_end misaligned")
 #endif
 
 ASSERT(IS_ALIGNED(cpu0_stack, STACK_SIZE), "cpu0_stack misaligned")
-- 
2.1.4


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