[Xen-devel] [PATCH] xen/x86: Construct the {l2, l3}_bootmap at compile time

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

... rather than at runtime.

The bootmaps are discarded in zap_low_mappings(), so the tables themselves can
live in .init.data and be reclaimed after boot.

Hooking the l1_identmap into l2_xenmap stays for safety, along with a longer
comment explaining why.

This does not change the EFI construction of {l2,l3}_bootmap.  EFI already
constructs them cleanly in their relocated form.

Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
---
CC: Jan Beulich <JBeulich@xxxxxxxx>

v2:
 * New
v3:
 * Expand commit message to indicate that EFI is unaffected.
---
 xen/arch/x86/boot/head.S   | 18 +++++-------------
 xen/arch/x86/boot/x86_64.S | 19 +++++++++++++++++++
 xen/arch/x86/x86_64/mm.c   |  4 ----
 3 files changed, 24 insertions(+), 17 deletions(-)

diff --git a/xen/arch/x86/boot/head.S b/xen/arch/x86/boot/head.S
index ac4962b..f3501fd 100644
--- a/xen/arch/x86/boot/head.S
+++ b/xen/arch/x86/boot/head.S
@@ -150,21 +150,13 @@ __start:
         mov     %eax,sym_phys(boot_tsc_stamp)
         mov     %edx,sym_phys(boot_tsc_stamp+4)
 
-        /* Initialise L2 boot-map page table entries (16MB). */
-        mov     $sym_phys(l2_bootmap),%edx
-        mov     $PAGE_HYPERVISOR|_PAGE_PSE,%eax
-        mov     $8,%ecx
-1:      mov     %eax,(%edx)
-        add     $8,%edx
-        add     $(1<<L2_PAGETABLE_SHIFT),%eax
-        loop    1b
-        /* Initialise L3 boot-map page directory entry. */
-        mov     $sym_phys(l2_bootmap)+__PAGE_HYPERVISOR,%eax
-        mov     %eax,sym_phys(l3_bootmap) + 0*8
-        /* Hook 4kB mappings of first 2MB of memory into L2. */
+        /*
+         * During boot, hook 4kB mappings of first 2MB of memory into L2.
+         * This avoids mixing cachability for the legacy VGA region, and is
+         * corrected when Xen relocates itself.
+         */
         mov     $sym_phys(l1_identmap)+__PAGE_HYPERVISOR,%edi
         mov     %edi,sym_phys(l2_xenmap)
-        mov     %edi,sym_phys(l2_bootmap)
 
         /* Apply relocations to bootstrap trampoline. */
         mov     sym_phys(trampoline_phys),%edx
diff --git a/xen/arch/x86/boot/x86_64.S b/xen/arch/x86/boot/x86_64.S
index 9df3902..9ab9231 100644
--- a/xen/arch/x86/boot/x86_64.S
+++ b/xen/arch/x86/boot/x86_64.S
@@ -184,3 +184,22 @@ GLOBAL(idle_pg_table)
         .size idle_pg_table, . - idle_pg_table
 
 GLOBAL(__page_tables_end)
+
+/* Init pagetables.  Enough page directories to map into the bottom 1GB. */
+        .section .init.data, "a", @progbits
+        .align PAGE_SIZE, 0
+
+GLOBAL(l2_bootmap)
+        .quad sym_phys(l1_identmap) + __PAGE_HYPERVISOR
+        idx = 1
+        .rept 7
+        .quad (idx << L2_PAGETABLE_SHIFT) | __PAGE_HYPERVISOR | _PAGE_PSE
+        idx = idx + 1
+        .endr
+        .fill L2_PAGETABLE_ENTRIES - 8, 8, 0
+        .size l2_bootmap, . - l2_bootmap
+
+GLOBAL(l3_bootmap)
+        .quad sym_phys(l2_bootmap) + __PAGE_HYPERVISOR
+        .fill L3_PAGETABLE_ENTRIES - 1, 8, 0
+        .size l3_bootmap, . - l3_bootmap
diff --git a/xen/arch/x86/x86_64/mm.c b/xen/arch/x86/x86_64/mm.c
index 2228898..e07e69e 100644
--- a/xen/arch/x86/x86_64/mm.c
+++ b/xen/arch/x86/x86_64/mm.c
@@ -42,10 +42,6 @@ asm(".file \"" __FILE__ "\"");
 
 unsigned int __read_mostly m2p_compat_vstart = __HYPERVISOR_COMPAT_VIRT_START;
 
-/* Enough page directories to map into the bottom 1GB. */
-l3_pgentry_t __section(".bss.page_aligned") l3_bootmap[L3_PAGETABLE_ENTRIES];
-l2_pgentry_t __section(".bss.page_aligned") l2_bootmap[L2_PAGETABLE_ENTRIES];
-
 l2_pgentry_t *compat_idle_pg_table_l2;
 
 void *do_page_walk(struct vcpu *v, unsigned long addr)
-- 
2.1.4


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