[Xen-devel] [PATCH v2 1/5] x86/boot: Create the l2_xenmap[] mappings dynamically

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

The build-time construction of l2_xenmap[] imposes an arbitrary limit of 16M
total, which is a limit looking to be lifted.

Move l2_xenmap[] into the BSS, and adjust both the BIOS and EFI paths to fill
it in dynamically, based on the final linked size of Xen.

Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
---
CC: Jan Beulich <JBeulich@xxxxxxxx>
CC: Wei Liu <wl@xxxxxxx>
CC: Roger Pau Monné <roger.pau@xxxxxxxxxx>

v2:
 * Rewrite several comments
---
 xen/arch/x86/boot/head.S    | 14 ++++++++++++++
 xen/arch/x86/boot/x86_64.S  | 23 ++++++++---------------
 xen/arch/x86/efi/efi-boot.h | 14 ++++++++++++++
 xen/arch/x86/xen.lds.S      |  3 +++
 4 files changed, 39 insertions(+), 15 deletions(-)

diff --git a/xen/arch/x86/boot/head.S b/xen/arch/x86/boot/head.S
index c5acbf56ae..ef9f562505 100644
--- a/xen/arch/x86/boot/head.S
+++ b/xen/arch/x86/boot/head.S
@@ -668,6 +668,20 @@ trampoline_setup:
         add     %esi,sym_fs(__page_tables_start)-8(,%ecx,8)
 2:      loop    1b
 
+        /* Map Xen into the higher mappings using 2M superpages. */
+        lea     _PAGE_PSE + PAGE_HYPERVISOR_RWX + sym_esi(_start), %eax
+        mov     $sym_offs(_start),   %ecx   /* %eax = PTE to write ^      */
+        mov     $sym_offs(_end - 1), %edx
+        shr     $L2_PAGETABLE_SHIFT, %ecx   /* %ecx = First slot to write */
+        shr     $L2_PAGETABLE_SHIFT, %edx   /* %edx = Final slot to write */
+
+1:      mov     %eax, sym_offs(l2_xenmap)(%esi, %ecx, 8)
+        add     $1, %ecx
+        add     $1 << L2_PAGETABLE_SHIFT, %eax
+
+        cmp     %edx, %ecx
+        jbe     1b
+
         /*
          * Map Xen into the directmap (needed for early-boot pagetable
          * handling/walking), and identity map Xen into bootmap (needed for
diff --git a/xen/arch/x86/boot/x86_64.S b/xen/arch/x86/boot/x86_64.S
index aabf561b23..e63bece460 100644
--- a/xen/arch/x86/boot/x86_64.S
+++ b/xen/arch/x86/boot/x86_64.S
@@ -43,6 +43,14 @@ multiboot_ptr:
 GLOBAL(stack_start)
         .quad   cpu0_stack + STACK_SIZE - CPUINFO_sizeof
 
+        .section .bss.page_aligned, "aw", @nobits
+        .align PAGE_SIZE, 0
+
+/* L2 mapping the Xen text/data/bss region.  Uses 1x 4k page. */
+GLOBAL(l2_xenmap)
+        .fill L2_PAGETABLE_ENTRIES, 8, 0
+        .size l2_xenmap, . - l2_xenmap
+
         .section .data.page_aligned, "aw", @progbits
         .align PAGE_SIZE, 0
 /*
@@ -80,21 +88,6 @@ GLOBAL(l2_directmap)
         .fill 4 * L2_PAGETABLE_ENTRIES - 1, 8, 0
         .size l2_directmap, . - l2_directmap
 
-/*
- * L2 mapping the 1GB Xen text/data/bss region.  At boot it maps 16MB from
- * __image_base__, and is modified when Xen relocates itself.  Uses 1x 4k
- * page.
- */
-GLOBAL(l2_xenmap)
-        .quad 0
-        idx = 1
-        .rept 7
-        .quad sym_offs(__image_base__) + (idx << L2_PAGETABLE_SHIFT) + 
(PAGE_HYPERVISOR_RWX | _PAGE_PSE)
-        idx = idx + 1
-        .endr
-        .fill L2_PAGETABLE_ENTRIES - 8, 8, 0
-        .size l2_xenmap, . - l2_xenmap
-
 /* L2 mapping the fixmap.  Uses 1x 4k page. */
 l2_fixmap:
         idx = 0
diff --git a/xen/arch/x86/efi/efi-boot.h b/xen/arch/x86/efi/efi-boot.h
index 50d1499867..ce07aedf45 100644
--- a/xen/arch/x86/efi/efi-boot.h
+++ b/xen/arch/x86/efi/efi-boot.h
@@ -585,6 +585,20 @@ static void __init efi_arch_memory_setup(void)
     if ( !efi_enabled(EFI_LOADER) )
         return;
 
+    /*
+     * Map Xen into the higher mappings, using 2M superpages.
+     *
+     * NB: We are currently in physical mode, so a RIP-relative relocation
+     * against _start/_end result in our arbitrary placement by the bootloader
+     * in memory, rather than the intended high mappings position.  Subtract
+     * xen_phys_start to get the appropriate slots in l2_xenmap[].
+     */
+    for ( i =  l2_table_offset((UINTN)_start   - xen_phys_start);
+          i <= l2_table_offset((UINTN)_end - 1 - xen_phys_start); ++i )
+        l2_xenmap[i] =
+            l2e_from_paddr(xen_phys_start + (i << L2_PAGETABLE_SHIFT),
+                           PAGE_HYPERVISOR_RWX | _PAGE_PSE);
+
     /* Check that there is at least 4G of mapping space in l2_*map[] */
     BUILD_BUG_ON((sizeof(l2_bootmap)   / L2_PAGETABLE_ENTRIES) < 4);
     BUILD_BUG_ON((sizeof(l2_directmap) / L2_PAGETABLE_ENTRIES) < 4);
diff --git a/xen/arch/x86/xen.lds.S b/xen/arch/x86/xen.lds.S
index 29ef507432..07c6448dbb 100644
--- a/xen/arch/x86/xen.lds.S
+++ b/xen/arch/x86/xen.lds.S
@@ -360,6 +360,9 @@ ASSERT(__2M_rwdata_end <= XEN_VIRT_END - XEN_VIRT_START + 
__XEN_VIRT_START -
 ASSERT(kexec_reloc_size - kexec_reloc <= PAGE_SIZE, "kexec_reloc is too large")
 #endif
 
+/* The Multiboot setup paths relies on this to simplify superpage PTE 
creation. */
+ASSERT(IS_ALIGNED(_start,            MB(2)), "_start misaligned")
+
 ASSERT(IS_ALIGNED(__2M_text_end,     SECTION_ALIGN), "__2M_text_end 
misaligned")
 ASSERT(IS_ALIGNED(__2M_rodata_start, SECTION_ALIGN), "__2M_rodata_start 
misaligned")
 ASSERT(IS_ALIGNED(__2M_rodata_end,   SECTION_ALIGN), "__2M_rodata_end 
misaligned")
-- 
2.11.0


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