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Re: [PATCH 2/2] pc-bios: s390x: Give precedence to reset PSW
From: |
Thomas Huth |
Subject: |
Re: [PATCH 2/2] pc-bios: s390x: Give precedence to reset PSW |
Date: |
Fri, 20 Nov 2020 07:02:38 +0100 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.12.0 |
On 19/11/2020 22.11, Eric Farman wrote:
>
>
> On 11/19/20 3:20 PM, Thomas Huth wrote:
>> On 19/11/2020 17.57, Eric Farman wrote:
>>> Let's look at the Reset PSW first instead of the contents of memory.
>>> It might be leftover from an earlier system boot when processing
>>> a chreipl.
>>>
>>> Signed-off-by: Eric Farman <farman@linux.ibm.com>
>>> ---
>>> pc-bios/s390-ccw/jump2ipl.c | 20 ++++++++++----------
>>> 1 file changed, 10 insertions(+), 10 deletions(-)
>>>
>>> diff --git a/pc-bios/s390-ccw/jump2ipl.c b/pc-bios/s390-ccw/jump2ipl.c
>>> index fbae45b03c..67b4afb6a0 100644
>>> --- a/pc-bios/s390-ccw/jump2ipl.c
>>> +++ b/pc-bios/s390-ccw/jump2ipl.c
>>> @@ -72,16 +72,6 @@ void jump_to_IPL_code(uint64_t address)
>>> void jump_to_low_kernel(void)
>>> {
>>> - /*
>>> - * If it looks like a Linux binary, i.e. there is the "S390EP" magic
>>> from
>>> - * arch/s390/kernel/head.S here, then let's jump to the well-known
>>> Linux
>>> - * kernel start address (when jumping to the PSW-at-zero address
>>> instead,
>>> - * the kernel startup code fails when we booted from a network device).
>>> - */
>>> - if (!memcmp((char *)0x10008, "S390EP", 6)) {
>>> - jump_to_IPL_code(KERN_IMAGE_START);
>>> - }
>>> -
>>> /* Trying to get PSW at zero address */
>>> if (*((uint64_t *)0) & RESET_PSW_MASK) {
>>> /*
>>> @@ -92,6 +82,16 @@ void jump_to_low_kernel(void)
>>> jump_to_IPL_code(0);
>>> }
>>> + /*
>>> + * If it looks like a Linux binary, i.e. there is the "S390EP" magic
>>> from
>>> + * arch/s390/kernel/head.S here, then let's jump to the well-known
>>> Linux
>>> + * kernel start address (when jumping to the PSW-at-zero address
>>> instead,
>>> + * the kernel startup code fails when we booted from a network device).
>>> + */
>>> + if (!memcmp((char *)0x10008, "S390EP", 6)) {
>>> + jump_to_IPL_code(KERN_IMAGE_START);
>>> + }
>>
>> That feels a little bit dangerous ... I assume the order has been that way
>> for a reason, e.g. I think we had to jump to KERN_IMAGE_START for some older
>> versions of the Linux kernel since the startup code that was referenced by
>> the PSW at address zero was not working in KVM...
>
> Makes sense. It does seem like a precarious piece of code.
>
>>
>> What do you think about this alternate idea instead: Clear the memory at
>> location 0x10008 at the very beginning of the main() function (or maybe in
>> boot_setup())?
>
> This seems to work too (I put it in boot_setup(), prior to call to
> store_iplb()).
Great, can you send the patch before your holidays next week? (If you don't
have enough time, that's ok, too, it's trivial enough, so I think I could
write such a patch, too)
Thomas
Re: [PATCH 0/2] pc-bios/s390 fixes for reboot-to-vfio-ccw, Cornelia Huck, 2020/11/19