Re: [GIT PULL] x86: add brk allocator for very early allocations

[Jeremy Fitzhardinge <jeremy@goop.org>]

Yinghai Lu wrote:
> could have more explanation about the 1M size.
> because initial_pg_tables will sit in it. please consider to add something like
>
> in head_32.S
>
>  LOW_PAGES = (KERNEL_IMAGE_SIZE + PAGE_SIZE_asm - 1)>>PAGE_SHIFT
>  
>  #if PTRS_PER_PMD > 1
>  PAGE_TABLE_SIZE = (LOW_PAGES / PTRS_PER_PMD) + PTRS_PER_PGD
>  #else
>  PAGE_TABLE_SIZE = (LOW_PAGES / PTRS_PER_PGD)
>  #endif
>  ALLOCATOR_SLOP = 4
>   

OK, how does this look:

The following changes since commit 21e8ba72daf5d7f0af33968f873499c85f96ccef:
  Jeremy Fitzhardinge (1):
        x86: use brk allocation for DMI

are available in the git repository at:

  git://git.kernel.org/pub/scm/linux/kernel/git/jeremy/xen.git push/x86/brk

Jeremy Fitzhardinge (1):
      x86: allow extend_brk users to reserve brk space

Yinghai Lu (1):
      x86-32: compute initial mapping size more accurately

 arch/x86/include/asm/page_32_types.h |    5 +++++
 arch/x86/include/asm/setup.h         |   30 ++++++++++++++++++++++++++++++
 arch/x86/kernel/head_32.S            |    4 +++-
 arch/x86/kernel/setup.c              |    2 ++
 arch/x86/kernel/vmlinux_32.lds.S     |    4 +++-
 arch/x86/kernel/vmlinux_64.lds.S     |    4 +++-
 6 files changed, 46 insertions(+), 3 deletions(-)

git diff 21e8ba72daf5d7f0af33968f873499c85f96ccef..push/x86/brk
diff --git a/arch/x86/include/asm/page_32_types.h b/arch/x86/include/asm/page_32_types.h
index f1e4a79..0f915ae 100644
--- a/arch/x86/include/asm/page_32_types.h
+++ b/arch/x86/include/asm/page_32_types.h
@@ -39,6 +39,11 @@
 #define __VIRTUAL_MASK_SHIFT	32
 #endif	/* CONFIG_X86_PAE */
 
+/*
+ * Kernel image size is limited to 512 MB (see in arch/x86/kernel/head_32.S)
+ */
+#define KERNEL_IMAGE_SIZE	(512 * 1024 * 1024)
+
 #ifndef __ASSEMBLY__
 
 /*
diff --git a/arch/x86/include/asm/setup.h b/arch/x86/include/asm/setup.h
index 366d366..61b126b 100644
--- a/arch/x86/include/asm/setup.h
+++ b/arch/x86/include/asm/setup.h
@@ -104,6 +104,29 @@ extern struct boot_params boot_params;
 extern unsigned long _brk_end;
 void *extend_brk(size_t size, size_t align);
 
+/*
+ * Reserve space in the brk section.  The name must be unique within
+ * the file, and somewhat descriptive.  The size is in bytes.  Must be
+ * used at file scope.
+ *
+ * (This uses a temp function to wrap the asm so we can pass it the
+ * size parameter; otherwise we wouldn't be able to.  We can't use a
+ * "section" attribute on a normal variable because it always ends up
+ * being @progbits, which ends up allocating space in the vmlinux
+ * executable.)
+ */
+#define RESERVE_BRK(name,sz)						\
+	static void __section(.discard) __used			\
+	__brk_reservation_fn_##name##__(void) {				\
+		asm volatile (						\
+			".pushsection .brk_reservation,\"aw\",@nobits;" \
+			"__brk_reservation_" #name "__:"		\
+			" 1:.skip %c0;"					\
+			" .size __brk_reservation_" #name "__, . - 1b;"	\
+			" .popsection"					\
+			: : "i" (sz));					\
+	}
+
 #ifdef __i386__
 
 void __init i386_start_kernel(void);
@@ -115,6 +138,13 @@ void __init x86_64_start_reservations(char *real_mode_data);
 
 #endif /* __i386__ */
 #endif /* _SETUP */
+#else
+#define RESERVE_BRK(name,sz)				\
+	.pushsection .brk_reservation,"aw",@nobits;	\
+__brk_reservation_##name##__:				\
+1:	.skip sz;					\
+	.size __brk_reservation_##name##__,.-1b;	\
+	.popsection
 #endif /* __ASSEMBLY__ */
 #endif  /*  __KERNEL__  */
 
diff --git a/arch/x86/kernel/head_32.S b/arch/x86/kernel/head_32.S
index d243437..80dc05e 100644
--- a/arch/x86/kernel/head_32.S
+++ b/arch/x86/kernel/head_32.S
@@ -54,7 +54,7 @@
  *
  * This should be a multiple of a page.
  */
-LOW_PAGES = 1<<(32-PAGE_SHIFT_asm)
+LOW_PAGES = (KERNEL_IMAGE_SIZE + PAGE_SIZE_asm - 1)>>PAGE_SHIFT
 
 /*
  * To preserve the DMA pool in PAGEALLOC kernels, we'll allocate
@@ -75,6 +75,8 @@ ALLOCATOR_SLOP = 4
 
 INIT_MAP_BEYOND_END = BOOTBITMAP_SIZE + (PAGE_TABLE_SIZE + ALLOCATOR_SLOP)*PAGE_SIZE_asm
 
+RESERVE_BRK(pagetables, PAGE_TABLE_SIZE * PAGE_SIZE)
+
 /*
  * 32-bit kernel entrypoint; only used by the boot CPU.  On entry,
  * %esi points to the real-mode code as a 32-bit pointer.
diff --git a/arch/x86/kernel/setup.c b/arch/x86/kernel/setup.c
index b344908..d633958 100644
--- a/arch/x86/kernel/setup.c
+++ b/arch/x86/kernel/setup.c
@@ -112,6 +112,8 @@
 #define ARCH_SETUP
 #endif
 
+RESERVE_BRK(dmi_alloc, 65536);
+
 unsigned int boot_cpu_id __read_mostly;
 
 static __initdata unsigned long _brk_start = (unsigned long)__brk_base;
diff --git a/arch/x86/kernel/vmlinux_32.lds.S b/arch/x86/kernel/vmlinux_32.lds.S
index 1063fbe..4005279 100644
--- a/arch/x86/kernel/vmlinux_32.lds.S
+++ b/arch/x86/kernel/vmlinux_32.lds.S
@@ -192,7 +192,8 @@ SECTIONS
 
 	. = ALIGN(PAGE_SIZE);
 	__brk_base = . ;
-	. += 1024 * 1024 ;
+ 	. += 64 * 1024 ;	/* 64k slop space */
+	*(.brk_reservation)	/* areas brk users have reserved */
 	__brk_limit = . ;
 
   	_end = . ;
@@ -201,6 +202,7 @@ SECTIONS
   /* Sections to be discarded */
   /DISCARD/ : {
 	*(.exitcall.exit)
+	*(.discard)
 	}
 
   STABS_DEBUG
diff --git a/arch/x86/kernel/vmlinux_64.lds.S b/arch/x86/kernel/vmlinux_64.lds.S
index b8b83e4..47deee3 100644
--- a/arch/x86/kernel/vmlinux_64.lds.S
+++ b/arch/x86/kernel/vmlinux_64.lds.S
@@ -250,7 +250,8 @@ SECTIONS
 
  	. = ALIGN(PAGE_SIZE);
  	__brk_base = . ;
- 	. += 1024 * 1024 ;
+ 	. += 64 * 1024 ;	/* 64k slop space */
+	*(.brk_reservation)	/* areas brk users have reserved */
  	__brk_limit = . ;
   }
 
@@ -260,6 +261,7 @@ SECTIONS
   /DISCARD/ : {
 	*(.exitcall.exit)
 	*(.eh_frame)
+	*(.discard)
 	}
 
   STABS_DEBUG