Re: Early memory patch, revised

[ebiederm@xmission.com (Eric W. Biederman)]

"H. Peter Anvin" <hpa@zytor.com> writes:

> Hi all,
> 
> This is the latest version of the i386 early memory cleanup patch.  It has the
> additional advantage that it removes some of the special casing for VISWS --
> this is still untested; if you have access to a VISWS *please* test this out.
> 
> The main difference other than the VISWS code is that it always sets up the GDT.
> 
> I agree with Eric this is a lot cleaner.

Thanks.  :)

Two little tweaks I can think of.
1) Can we reserve space between __bss_stop and _end for the page
   tables and the bitmap of memory?   
   
   This should make it obvious that the early boot code is touching
   that memory.

2) Can we export _end in setup.S so a bootloader can verify the
   kernel + bss will fit in memory?

Roughly the additions needed to vmlinux.lds.S look like:
+++ arch/i386/kernel/vmlinux.lds.S
@@ -105,6 +105,18 @@
 	
   __bss_start = .;		/* BSS */
   .bss : { *(.bss) }
+  . = ALIGN(4);
   __bss_stop = .; 
+ 
+  /* Reserve space for the initial page tables.
+   * A 1GB kernel needs 1MB of page tables.
+   * We must cover the first 1M ourselves and the initial memory bitmap.
+   * In the worst (1G kernel + 36G of ram) case this increases our
+   * page table size by 3K.
+   */
+  . += (((__bss_stop - _text + 4095) / 4096) + ((4*1024*1024) / 4096)) * 4 ;
+  
+  /* Reserve space for the initial memory bitmap 2^36/4096/8 = 2MB */
+  . += 2*1024*1024;
 
   _end = . ;

Eric