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Re: [Qemu-devel] [PATCH for-4.0 v4 4/4] i386: allow to load initrd below
From: |
Michael S. Tsirkin |
Subject: |
Re: [Qemu-devel] [PATCH for-4.0 v4 4/4] i386: allow to load initrd below 4G for recent linux |
Date: |
Fri, 21 Dec 2018 11:10:30 -0500 |
On Thu, Dec 06, 2018 at 10:32:13AM +0800, Li Zhijian wrote:
> a new field xloadflags was added to recent x86 linux, and BIT 1:
> XLF_CAN_BE_LOADED_ABOVE_4G is used to tell bootload that where initrd can be
> loaded safely.
>
> Current QEMU/BIOS always loads initrd below below_4g_mem_size which is always
> less than 4G, so here limiting initrd_max to 4G - 1 simply is enough if
> this bit is set.
>
> CC: Paolo Bonzini <address@hidden>
> CC: Richard Henderson <address@hidden>
> CC: Eduardo Habkost <address@hidden>
> CC: "Michael S. Tsirkin" <address@hidden>
> CC: Marcel Apfelbaum <address@hidden>
> Signed-off-by: Li Zhijian <address@hidden>
>
> ---
> V3: correct grammar and check XLF_CAN_BE_LOADED_ABOVE_4G first (Michael S.
> Tsirkin)
>
> Signed-off-by: Li Zhijian <address@hidden>
> ---
> hw/i386/pc.c | 10 +++++++++-
> 1 file changed, 9 insertions(+), 1 deletion(-)
>
> diff --git a/hw/i386/pc.c b/hw/i386/pc.c
> index 3b10726..baa99c0 100644
> --- a/hw/i386/pc.c
> +++ b/hw/i386/pc.c
> @@ -904,7 +904,15 @@ static void load_linux(PCMachineState *pcms,
> #endif
>
> /* highest address for loading the initrd */
> - if (protocol >= 0x203) {
> + if (protocol >= 0x20c &&
> + lduw_p(header+0x236) & XLF_CAN_BE_LOADED_ABOVE_4G) {
> + /*
> + * Although kernel allows initrd loading to above 4G,
> + * it just makes it as large as possible while still staying below 4G
> + * since current BIOS always loads initrd below
> pcms->below_4g_mem_size
> + */
> + initrd_max = UINT32_MAX;
> + } else if (protocol >= 0x203) {
> initrd_max = ldl_p(header+0x22c);
> } else {
> initrd_max = 0x37ffffff;
I still have trouble understanding the above.
Anyone else wants to comment / help rephrase the comment
and commit log so it's readable?
> --
> 2.7.4