[PATCH] i386: Implement CONFIG_PHYSICAL_ALIGN

o Now CONFIG_PHYSICAL_START is being replaced with CONFIG_PHYSICAL_ALIGN.
  Hardcoding the kernel physical start value creates a problem in relocatable
  kernel context due to boot loader limitations. For ex, if somebody
  compiles a relocatable kernel to be run from address 4MB, but this kernel
  will run from location 1MB as grub loads the kernel at physical address
  1MB. Kernel thinks that I am a relocatable kernel and I should run from
  the address I have been loaded at. So somebody wanting to run kernel
  from 4MB alignment location (for improved performance regions) can't do
  that.

o Hence, Eric proposed that probably CONFIG_PHYSICAL_ALIGN will make
  more sense in relocatable kernel context. At run time kernel will move
  itself to a physical addr location which meets user specified alignment
  restrictions.

Signed-off-by: Vivek Goyal <vgoyal@in.ibm.com>
Signed-off-by: Andi Kleen <ak@suse.de>

1 files changed, 18 insertions, 15 deletions

diff --git a/arch/i386/Kconfig b/arch/i386/Kconfig
index d588ca874bb4..fd2fa7a7ec52 100644
--- a/arch/i386/Kconfig
+++ b/arch/i386/Kconfig
@@ -785,23 +785,26 @@ config RELOCATABLE
           must live at a different physical address than the primary
           kernel.
 
-config PHYSICAL_START
-        hex "Physical address where the kernel is loaded" if (EMBEDDED || CRASH_DUMP)
-
-        default "0x1000000" if CRASH_DUMP
+config PHYSICAL_ALIGN
+        hex "Alignment value to which kernel should be aligned"
         default "0x100000"
+        range 0x2000 0x400000
         help
-          This gives the physical address where the kernel is loaded. Normally
-          for regular kernels this value is 0x100000 (1MB). But in the case
-          of kexec on panic the fail safe kernel needs to run at a different
-          address than the panic-ed kernel. This option is used to set the load
-          address for kernels used to capture crash dump on being kexec'ed
-          after panic. The default value for crash dump kernels is
-          0x1000000 (16MB). This can also be set based on the "X" value as
-          specified in the "crashkernel=YM@XM" command line boot parameter
-          passed to the panic-ed kernel. Typically this parameter is set as
-          crashkernel=64M@16M. Please take a look at
-          Documentation/kdump/kdump.txt for more details about crash dumps.
+          This value puts the alignment restrictions on physical address
+          where kernel is loaded and run from. Kernel is compiled for an
+          address which meets above alignment restriction.
+
+          If bootloader loads the kernel at a non-aligned address and
+          CONFIG_RELOCATABLE is set, kernel will move itself to nearest
+          address aligned to above value and run from there.
+
+          If bootloader loads the kernel at a non-aligned address and
+          CONFIG_RELOCATABLE is not set, kernel will ignore the run time
+          load address and decompress itself to the address it has been
+          compiled for and run from there. The address for which kernel is
+          compiled already meets above alignment restrictions. Hence the
+          end result is that kernel runs from a physical address meeting
+          above alignment restrictions.
 
           Don't change this unless you know what you are doing.