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Re: [Qemu-devel] [PATCH for-4.0 v4 0/4] allow to load initrd below 4G fo

From: Li Zhijian
Subject: Re: [Qemu-devel] [PATCH for-4.0 v4 0/4] allow to load initrd below 4G for recent kernel
Date: Fri, 21 Dec 2018 09:37:28 +0800
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.2.1


On 12/6/18 10:32, Li Zhijian wrote:
Long long ago, linux kernel has supported up to 4G initrd, but it's header
still hard code to allow loading initrd below 2G only.
  cutting from arch/x86/head.S:
  # (Header version 0x0203 or later) the highest safe address for the contents
  # of an initrd. The current kernel allows up to 4 GB, but leave it at 2 GB to
  # avoid possible bootloader bugs.

In order to support more than 2G initrd, qemu must allow loading initrd
above 2G address. Luckly, recent kernel introduced a new field to linux header
named xloadflags:XLF_CAN_BE_LOADED_ABOVE_4G which tells bootload an optional
and safe address to load initrd.

Current QEMU/BIOS always loads initrd below below_4g_mem_size which always
less than 4G, so here limiting initrd_max to 4G - 1 simply is enough if
this bit is set.

Default roms(Seabios + optionrom(linuxboot_dma)) works as expected with this

   - add Reviwed-by tag to 1/4 and 2/4
   - use scripts/update-linux-headers.sh to import bootparam.h
   - minor fix at commit log
  - rebase code basing on http://patchwork.ozlabs.org/cover/1005990 and
  - add new patch 3/4 to import header bootparam.h (Michael S. Tsirkin)

V2: add 2 patches(3/5, 4/5) to fix potential loading issue.

Li Zhijian (4):
   unify len and addr type for memory/address APIs
   refactor load_image_size
   i386: import & use bootparam.h
   i386: allow to load initrd below 4G for recent linux

  exec.c                                       | 47 ++++++++++++++--------------
  hw/core/loader.c                             | 11 +++----
  hw/i386/pc.c                                 | 18 ++++++-----
  include/exec/cpu-all.h                       |  2 +-
  include/exec/cpu-common.h                    |  8 ++---
  include/exec/memory.h                        | 22 ++++++-------
  include/standard-headers/asm-x86/bootparam.h | 34 ++++++++++++++++++++
  scripts/update-linux-headers.sh              |  4 +++
  8 files changed, 92 insertions(+), 54 deletions(-)
  create mode 100644 include/standard-headers/asm-x86/bootparam.h

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