Commit ceefccc9 authored by H. Peter Anvin's avatar H. Peter Anvin
Browse files

x86: default CONFIG_PHYSICAL_START and CONFIG_PHYSICAL_ALIGN to 16 MB 



Default CONFIG_PHYSICAL_START and CONFIG_PHYSICAL_ALIGN each to 16 MB,
so that both non-relocatable and relocatable kernels are loaded at
16 MB by a non-relocating bootloader.  This is somewhat hacky, but it
appears to be the only way to do this that does not break some some
set of existing bootloaders.

We want to avoid the bottom 16 MB because of large page breakup,
memory holes, and ZONE_DMA.  Embedded systems may need to reduce this,
or update their bootloaders to be aware of the new min_alignment field.

[ Impact: performance improvement, avoids problems on some systems ]

Signed-off-by: default avatarH. Peter Anvin <hpa@zytor.com>
parent d297366b

arch/x86/Kconfig

+12 −15
Original line number Diff line number Diff line
@@ -1455,9 +1455,7 @@ config KEXEC_JUMP 


config PHYSICAL_START

	hex "Physical address where the kernel is loaded" if (EMBEDDED || CRASH_DUMP)

	default "0x1000000" if X86_NUMAQ

	default "0x200000" if X86_64

	default "0x100000"

	default "0x1000000"

	---help---

	  This gives the physical address where the kernel is loaded.
@@ -1476,15 +1474,15 @@ config PHYSICAL_START 
	  to be specifically compiled to run from a specific memory area

	  (normally a reserved region) and this option comes handy.



	  So if you are using bzImage for capturing the crash dump, leave

	  the value here unchanged to 0x100000 and set CONFIG_RELOCATABLE=y.

	  Otherwise if you plan to use vmlinux for capturing the crash dump

	  change this value to start of the reserved region (Typically 16MB

	  0x1000000). In other words, it can 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.

	  So if you are using bzImage for capturing the crash dump,

	  leave the value here unchanged to 0x1000000 and set

	  CONFIG_RELOCATABLE=y.  Otherwise if you plan to use vmlinux

	  for capturing the crash dump change this value to start of

	  the reserved region.  In other words, it can be set based on

	  the "X" value as specified in the "crashkernel=YM@XM"

	  command line boot parameter passed to the panic-ed

	  kernel. Please take a look at Documentation/kdump/kdump.txt

	  for more details about crash dumps.



	  Usage of bzImage for capturing the crash dump is recommended as

	  one does not have to build two kernels. Same kernel can be used
@@ -1521,9 +1519,8 @@ config X86_NEED_RELOCS 
config PHYSICAL_ALIGN

	hex

	prompt "Alignment value to which kernel should be aligned" if X86_32

	default "0x100000" if X86_32

	default "0x200000" if X86_64

	range 0x2000 0x400000

	default "0x1000000"

	range 0x2000 0x1000000

	---help---

	  This value puts the alignment restrictions on physical address

	  where kernel is loaded and run from. Kernel is compiled for an

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