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Re: [Qemu-arm] [PATCH v2 3/4] hw/arm/boot: Avoid placing the initrd on t
From: |
Mark Rutland |
Subject: |
Re: [Qemu-arm] [PATCH v2 3/4] hw/arm/boot: Avoid placing the initrd on top of the kernel |
Date: |
Fri, 19 Jul 2019 17:47:30 +0100 |
User-agent: |
Mutt/1.11.1+11 (2f07cb52) (2018-12-01) |
Hi Peter,
I've just been testing on QEMU v4.1.0-rc1, and found a case where the
DTB overlapped the end of the kernel, and I think there's a bug in this
patch -- explanation below.
On Thu, May 16, 2019 at 03:47:32PM +0100, Peter Maydell wrote:
> We currently put the initrd at the smaller of:
> * 128MB into RAM
> * halfway into the RAM
> (with the dtb following it).
>
> However for large kernels this might mean that the kernel
> overlaps the initrd. For some kinds of kernel (self-decompressing
> 32-bit kernels, and ELF images with a BSS section at the end)
> we don't know the exact size, but even there we have a
> minimum size. Put the initrd at least further into RAM than
> that. For image formats that can give us an exact kernel size, this
> will mean that we definitely avoid overlaying kernel and initrd.
>
> Signed-off-by: Peter Maydell <address@hidden>
> ---
> hw/arm/boot.c | 34 ++++++++++++++++++++--------------
> 1 file changed, 20 insertions(+), 14 deletions(-)
>
> diff --git a/hw/arm/boot.c b/hw/arm/boot.c
> index 935be3b92a5..e441393fdf5 100644
> --- a/hw/arm/boot.c
> +++ b/hw/arm/boot.c
> @@ -999,20 +999,6 @@ static void arm_setup_direct_kernel_boot(ARMCPU *cpu,
> if (info->nb_cpus == 0)
> info->nb_cpus = 1;
>
> - /*
> - * We want to put the initrd far enough into RAM that when the
> - * kernel is uncompressed it will not clobber the initrd. However
> - * on boards without much RAM we must ensure that we still leave
> - * enough room for a decent sized initrd, and on boards with large
> - * amounts of RAM we must avoid the initrd being so far up in RAM
> - * that it is outside lowmem and inaccessible to the kernel.
> - * So for boards with less than 256MB of RAM we put the initrd
> - * halfway into RAM, and for boards with 256MB of RAM or more we put
> - * the initrd at 128MB.
> - */
> - info->initrd_start = info->loader_start +
> - MIN(info->ram_size / 2, 128 * 1024 * 1024);
> -
> /* Assume that raw images are linux kernels, and ELF images are not. */
> kernel_size = arm_load_elf(info, &elf_entry, &elf_low_addr,
> &elf_high_addr, elf_machine, as);
> @@ -1064,6 +1050,26 @@ static void arm_setup_direct_kernel_boot(ARMCPU *cpu,
> }
>
> info->entry = entry;
Note: this is the start of the kernel image...
> +
> + /*
> + * We want to put the initrd far enough into RAM that when the
> + * kernel is uncompressed it will not clobber the initrd. However
> + * on boards without much RAM we must ensure that we still leave
> + * enough room for a decent sized initrd, and on boards with large
> + * amounts of RAM we must avoid the initrd being so far up in RAM
> + * that it is outside lowmem and inaccessible to the kernel.
> + * So for boards with less than 256MB of RAM we put the initrd
> + * halfway into RAM, and for boards with 256MB of RAM or more we put
> + * the initrd at 128MB.
> + * We also refuse to put the initrd somewhere that will definitely
> + * overlay the kernel we just loaded, though for kernel formats which
> + * don't tell us their exact size (eg self-decompressing 32-bit kernels)
> + * we might still make a bad choice here.
> + */
> + info->initrd_start = info->loader_start +
> + MAX(MIN(info->ram_size / 2, 128 * 1024 * 1024), kernel_size);
... but here we add kernel_size to the start of the loader, which is
below the kernel. Should that be info->entry?
I've seen this trigger a case where:
* The kernel's image_size is 0x0a7a8000
* The kernel was loaded at 0x40080000
* The end of the kernel is 0x4A828000
* The DTB was loaded at 0x4a800000
... and the kernel is unable to find a usable DTB.
Thanks,
Mark.
> + info->initrd_start = TARGET_PAGE_ALIGN(info->initrd_start);
> +
> if (is_linux) {
> uint32_t fixupcontext[FIXUP_MAX];
>
> --
> 2.20.1
>
- Re: [Qemu-arm] [PATCH v2 3/4] hw/arm/boot: Avoid placing the initrd on top of the kernel,
Mark Rutland <=