Kexec on arm64

[Arun Chandran]

On Tue, Jul 29, 2014 at 7:05 PM, Mark Rutland <mark.rutland at arm.com> wrote:
> [...]
>
>> 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.
>

Ok. TEXT_OFFSET macro is not exported, that's why I used SZ_512K.
Any particular reason for not exporting it?

> 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?

For the 1st and second stage I use the same kernel as they
are combined with intramfs final image size varies.

1st stage
-------------
$ls -l arch/arm64/boot/uImage
-rw-rw-r-- 1 arun arun 12895544 Jul 30 10:57 arch/arm64/boot/uImage

It will boot to intramfs

$ls /
bin  dtb.dtb  home  lib    linuxrc  mnt  proc  run   share  tmp  var
dev  etc      init  lib64  media    opt  root  sbin  sys    usr  vmlinux.strip

kexec will boot vmlinux.strip
$ls -l vmlinux.strip
-rwxrwxr-x 1 arun arun 8194760 Jul 30 10:55 vmlinux.strip

2nd stage
--------------
$ls -l arch/arm64/boot/uImage
-rw-rw-r-- 1 arun arun 8127800 Jul 30 10:54 arch/arm64/boot/uImage

The corresponding vmlinux is converted to vmlinux.strip

$aarch64-linux-gnu-strip vmlinux -o vmlinux.strip
$cp vmlinux.strip /ramfs/aarch64_le_rootfs/

--Arun