Kexec on arm64

[mark.rutland@arm.com (Mark Rutland)]

[...]

> The default code did not work.
> 
> It is working with the change below
> 
> ###############
> diff --git a/arch/arm64/kernel/machine_kexec.c
> b/arch/arm64/kernel/machine_kexec.c
> index 5632473..7c5f859 100644
> --- a/arch/arm64/kernel/machine_kexec.c
> +++ b/arch/arm64/kernel/machine_kexec.c
> @@ -147,12 +147,17 @@ static bool kexec_is_dtb_user(const dtb_t *dtb)
>  /**
>   * kexec_list_walk - Helper to walk the kimage page list.
>   */
> -
> +static int kexec_kernel_size;
> +#define IMG_SIZE_NONE  0
> +#define KERN_SIZE_FLAG 1
> +#define DTB_SIZE_FLAG  2
>  static void kexec_list_walk(void *ctx, unsigned long kimage_head,
>         void (*cb)(void *ctx, unsigned int flag, void *addr, void *dest))
>  {
>         void *dest;
>         unsigned long *entry;
> +       int imgsize_flag = IMG_SIZE_NONE;
> +
> 
>         for (entry = &kimage_head, dest = NULL; ; entry++) {
>                 unsigned int flag = *entry & IND_FLAGS;
> @@ -164,10 +169,18 @@ static void kexec_list_walk(void *ctx, unsigned
> long kimage_head,
>                         cb(ctx, flag, addr, NULL);
>                         break;
>                 case IND_DESTINATION:
> +                       if (imgsize_flag == IMG_SIZE_NONE) {
> +                               kexec_kernel_size = 0;
> +                               imgsize_flag = KERN_SIZE_FLAG;
> +                       } else if (imgsize_flag == KERN_SIZE_FLAG) {
> +                               imgsize_flag = DTB_SIZE_FLAG;
> +                       }
>                         dest = addr;
>                         cb(ctx, flag, addr, NULL);
>                         break;
>                 case IND_SOURCE:
> +                       if (imgsize_flag == KERN_SIZE_FLAG)
> +                               kexec_kernel_size++;
>                         cb(ctx, flag, addr, dest);
>                         dest += PAGE_SIZE;
>                         break;
> @@ -693,5 +706,20 @@ void machine_kexec(struct kimage *image)
> 
>         kexec_list_walk(NULL, image->head, kexec_list_flush_cb);
> 
> +       /*
> +        * Make sure virtual addresses of new kernel are flushed
> +        * SZ_512K = TEXT_OFFSET

TEXT_OFFSET is not guaranteed to be 512K. The TEXT_OFFSET area also
shouldn't need to be flushed.

Since c218bca74eea (arm64: Relax the kernel cache requirements for
boot), the kernel will flush the cache for anything outside of the Image
that it writes to before enabling the MMU and caches (e.g. the idmap and
swapper page tables). Once caches are up we shouldn't care.

Assuming that the existing kernel code is correct, the only region we
should need to flush out to the PoC is the region from _text to _edata
(i.e. just the contents of the Image).

> +        * kexec_kernel = kexec_kernel_size * PAGE_SIZE
> +        * Don't know = (SZ_4M + SZ_1M)
> +        * SZ_4M = not working
> +        * SZ_6M = working
> +        * SZ_8M = working
> +        *
> +        * so chose SZ_4M + SZ_1M; Don't know why this is required
> +        * BSS, stack ??
> +        *
> +        */
> +       __flush_dcache_area((void *)PAGE_OFFSET, SZ_512K +
> (kexec_kernel_size * PAGE_SIZE) + SZ_4M + SZ_1M);
> +
>         soft_restart(reboot_code_buffer_phys);
>  }

How big exactly is the kernel Image you're trying to kexec?

Mark.