[PATCH] xen/x86: Use 2M superpages for text/data/bss mappings

[Andrew Cooper <andrew.cooper3@citrix.com>]

This balloons the size of Xen in memory from 3.4MB to 12MB, because of the
required alignment adjustments.

However
 * All mappings are 2M superpages.
 * .text (and .init at boot) are the only sections marked executable.
 * .text and .rodata are marked read-only.

Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
---
CC: Jan Beulich <JBeulich@suse.com>
---
 xen/arch/x86/setup.c     | 44 +++++++++++++++++++++++++++++++++++++++++---
 xen/arch/x86/xen.lds.S   | 33 +++++++++++++++++++++++++++++++++
 xen/include/xen/kernel.h |  6 ++++++
 3 files changed, 80 insertions(+), 3 deletions(-)

diff --git a/xen/arch/x86/setup.c b/xen/arch/x86/setup.c
index cddf954..c360fbc 100644
--- a/xen/arch/x86/setup.c
+++ b/xen/arch/x86/setup.c
@@ -921,13 +921,51 @@ void __init noreturn __start_xen(unsigned long mbi_p)
             /* The only data mappings to be relocated are in the Xen area. */
             pl2e = __va(__pa(l2_xenmap));
             *pl2e++ = l2e_from_pfn(xen_phys_start >> PAGE_SHIFT,
-                                   PAGE_HYPERVISOR_RWX | _PAGE_PSE);
+                                   PAGE_HYPERVISOR_RX | _PAGE_PSE);
             for ( i = 1; i < L2_PAGETABLE_ENTRIES; i++, pl2e++ )
             {
+                unsigned int flags;
+
                 if ( !(l2e_get_flags(*pl2e) & _PAGE_PRESENT) )
                     continue;
-                *pl2e = l2e_from_intpte(l2e_get_intpte(*pl2e) +
-                                        xen_phys_start);
+
+                if ( /*
+                      * Should be:
+                      *
+                      * i >= l2_table_offset((unsigned long)&__2M_text_start) &&
+                      *
+                      * but the EFI build can't manage the relocation.  It
+                      * evaluates to 0, so just use the upper bound.
+                      */
+                     i < l2_table_offset((unsigned long)&__2M_text_end) )
+                {
+                    flags = PAGE_HYPERVISOR_RX | _PAGE_PSE;
+                }
+                else if ( i >= l2_table_offset((unsigned long)&__2M_rodata_start) &&
+                          i <  l2_table_offset((unsigned long)&__2M_rodata_end) )
+                {
+                    flags = PAGE_HYPERVISOR_RO | _PAGE_PSE;
+                }
+                else if ( (i >= l2_table_offset((unsigned long)&__2M_data_start) &&
+                           i <  l2_table_offset((unsigned long)&__2M_data_end)) ||
+                          (i >= l2_table_offset((unsigned long)&__2M_bss_start) &&
+                           i <  l2_table_offset((unsigned long)&__2M_bss_end)) )
+                {
+                    flags = PAGE_HYPERVISOR_RW | _PAGE_PSE;
+                }
+                else if ( i >= l2_table_offset((unsigned long)&__2M_init_start) &&
+                          i <  l2_table_offset((unsigned long)&__2M_init_end) )
+                {
+                    flags = PAGE_HYPERVISOR_RWX | _PAGE_PSE;
+                }
+                else
+                {
+                    *pl2e = l2e_empty();
+                    continue;
+                }
+
+                *pl2e = l2e_from_paddr(
+                    l2e_get_paddr(*pl2e) + xen_phys_start, flags);
             }
 
             /* Re-sync the stack and then switch to relocated pagetables. */
diff --git a/xen/arch/x86/xen.lds.S b/xen/arch/x86/xen.lds.S
index 9fde1db..6c23c02 100644
--- a/xen/arch/x86/xen.lds.S
+++ b/xen/arch/x86/xen.lds.S
@@ -38,6 +38,9 @@ SECTIONS
   . = __XEN_VIRT_START;
   __image_base__ = .;
 #endif
+
+  __2M_text_start = .;         /* Start of 2M superpages, mapped RX. */
+
   . = __XEN_VIRT_START + MB(1);
   _start = .;
   .text : {
@@ -50,6 +53,10 @@ SECTIONS
        _etext = .;             /* End of text section */
   } :text = 0x9090
 
+  . = ALIGN(MB(2));
+  __2M_text_end = .;
+
+  __2M_rodata_start = .;       /* Start of 2M superpages, mapped RO. */
   .rodata : {
        /* Bug frames table */
        . = ALIGN(4);
@@ -67,6 +74,10 @@ SECTIONS
        *(.rodata.*)
   } :text
 
+  . = ALIGN(MB(2));
+  __2M_rodata_end = .;
+
+  __2M_data_start = .;         /* Start of 2M superpages, mapped RW. */
   . = ALIGN(SMP_CACHE_BYTES);
   .data.read_mostly : {
        /* Exception table */
@@ -104,6 +115,10 @@ SECTIONS
   __lock_profile_end = .;
 #endif
 
+  . = ALIGN(MB(2));
+  __2M_data_end = .;
+
+  __2M_init_start = .;         /* Start of 2M superpages, mapped RWX (boot only). */
   . = ALIGN(PAGE_SIZE);             /* Init code and data */
   __init_begin = .;
   .init.text : {
@@ -166,6 +181,10 @@ SECTIONS
   . = ALIGN(STACK_SIZE);
   __init_end = .;
 
+  . = ALIGN(MB(2));
+  __2M_init_end = .;
+
+  __2M_bss_start = .;          /* Start of 2M superpages, mapped RW. */
   .bss : {                     /* BSS */
        __bss_start = .;
        *(.bss.stack_aligned)
@@ -183,6 +202,9 @@ SECTIONS
   } :text
   _end = . ;
 
+  . = ALIGN(MB(2));
+  __2M_bss_end = .;
+
 #ifdef EFI
   . = ALIGN(4);
   .reloc : {
@@ -229,4 +251,15 @@ ASSERT(__image_base__ > XEN_VIRT_START ||
 ASSERT(kexec_reloc_size - kexec_reloc <= PAGE_SIZE, "kexec_reloc is too large")
 #endif
 
+ASSERT(IS_ALIGNED(__2M_text_start,   MB(2)), "__2M_text_start misaligned")
+ASSERT(IS_ALIGNED(__2M_text_end,     MB(2)), "__2M_text_end misaligned")
+ASSERT(IS_ALIGNED(__2M_rodata_start, MB(2)), "__2M_rodata_start misaligned")
+ASSERT(IS_ALIGNED(__2M_rodata_end,   MB(2)), "__2M_rodata_end misaligned")
+ASSERT(IS_ALIGNED(__2M_data_start,   MB(2)), "__2M_data_start misaligned")
+ASSERT(IS_ALIGNED(__2M_data_end,     MB(2)), "__2M_data_end misaligned")
+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_bss_start,    MB(2)), "__2M_bss_start misaligned")
+ASSERT(IS_ALIGNED(__2M_bss_end,      MB(2)), "__2M_bss_end misaligned")
+
 ASSERT(IS_ALIGNED(cpu0_stack, STACK_SIZE), "cpu0_stack misaligned")
diff --git a/xen/include/xen/kernel.h b/xen/include/xen/kernel.h
index 548b64d..8d08eca 100644
--- a/xen/include/xen/kernel.h
+++ b/xen/include/xen/kernel.h
@@ -65,6 +65,12 @@
 	1;                                      \
 })
 
+extern unsigned long __2M_text_start[], __2M_text_end[];
+extern unsigned long __2M_rodata_start[], __2M_rodata_end[];
+extern unsigned long __2M_data_start[], __2M_data_end[];
+extern unsigned long __2M_init_start[], __2M_init_end[];
+extern unsigned long __2M_bss_start[], __2M_bss_end[];
+
 extern char _start[], _end[], start[];
 #define is_kernel(p) ({                         \
     char *__p = (char *)(unsigned long)(p);     \
-- 
2.1.4