i386: paravirt boot sequence

This patch uses the updated boot protocol to do paravirtualized boot.
If the boot version is >= 2.07, then it will do two things:

 1. Check the bootparams loadflags to see if we should reload the
    segment registers and clear interrupts.  This is appropriate
    for normal native boot and some paravirtualized environments, but
    inapproprate for others.

 2. Check the hardware architecture, and dispatch to the appropriate
    kernel entrypoint.  If the bootloader doesn't set this, then we
    simply do the normal boot sequence.

Signed-off-by: Jeremy Fitzhardinge <jeremy@xensource.com>
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
Acked-by: H. Peter Anvin <hpa@zytor.com>
Cc: "Eric W. Biederman" <ebiederm@xmission.com>
Cc: Vivek Goyal <vgoyal@in.ibm.com>
Cc: James Bottomley <James.Bottomley@HansenPartnership.com>
Cc: Zachary Amsden <zach@vmware.com>
Cc: Andi Kleen <ak@suse.de>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 41 insertions, 3 deletions

diff --git a/arch/x86/kernel/head_32.S b/arch/x86/kernel/head_32.S
index 39677965e161..00b1c2c56454 100644
--- a/arch/x86/kernel/head_32.S
+++ b/arch/x86/kernel/head_32.S
@@ -79,22 +79,30 @@ INIT_MAP_BEYOND_END = BOOTBITMAP_SIZE + (PAGE_TABLE_SIZE + ALLOCATOR_SLOP)*PAGE_
  */
 .section .text.head,"ax",@progbits
 ENTRY(startup_32)
+        /* check to see if KEEP_SEGMENTS flag is meaningful */
+        cmpw $0x207, BP_version(%esi)
+        jb 1f
+
+        /* test KEEP_SEGMENTS flag to see if the bootloader is asking
+                us to not reload segments */
+        testb $(1<<6), BP_loadflags(%esi)
+        jnz 2f
 
 /*
  * Set segments to known values.
  */
-        cld
-        lgdt boot_gdt_descr - __PAGE_OFFSET
+1:      lgdt boot_gdt_descr - __PAGE_OFFSET
         movl $(__BOOT_DS),%eax
         movl %eax,%ds
         movl %eax,%es
         movl %eax,%fs
         movl %eax,%gs
+2:
 
 /*
  * Clear BSS first so that there are no surprises...
- * No need to cld as DF is already clear from cld above...
  */
+        cld
         xorl %eax,%eax
         movl $__bss_start - __PAGE_OFFSET,%edi
         movl $__bss_stop - __PAGE_OFFSET,%ecx
@@ -128,6 +136,35 @@ ENTRY(startup_32)
         movsl
 1:
 
+#ifdef CONFIG_PARAVIRT
+        cmpw $0x207, (boot_params + BP_version - __PAGE_OFFSET)
+        jb default_entry
+
+        /* Paravirt-compatible boot parameters.  Look to see what architecture
+                we're booting under. */
+        movl (boot_params + BP_hardware_subarch - __PAGE_OFFSET), %eax
+        cmpl $num_subarch_entries, %eax
+        jae bad_subarch
+
+        movl subarch_entries - __PAGE_OFFSET(,%eax,4), %eax
+        subl $__PAGE_OFFSET, %eax
+        jmp *%eax
+
+bad_subarch:
+WEAK(lguest_entry)
+WEAK(xen_entry)
+        /* Unknown implementation; there's really
+           nothing we can do at this point. */
+        ud2a
+.data
+subarch_entries:
+        .long default_entry             /* normal x86/PC */
+        .long lguest_entry              /* lguest hypervisor */
+        .long xen_entry                 /* Xen hypervisor */
+num_subarch_entries = (. - subarch_entries) / 4
+.previous
+#endif /* CONFIG_PARAVIRT */
+
 /*
  * Initialize page tables.  This creates a PDE and a set of page
  * tables, which are located immediately beyond _end.  The variable
@@ -140,6 +177,7 @@ ENTRY(startup_32)
  */
 page_pde_offset = (__PAGE_OFFSET >> 20);
 
+default_entry:
         movl $(pg0 - __PAGE_OFFSET), %edi
         movl $(swapper_pg_dir - __PAGE_OFFSET), %edx
         movl $0x007, %eax                       /* 0x007 = PRESENT+RW+USER */