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Re: [PATCH v2 2/2] pc-bios: s390x: Clear out leftover S390EP string

From: Christian Borntraeger
Subject: Re: [PATCH v2 2/2] pc-bios: s390x: Clear out leftover S390EP string
Date: Mon, 23 Nov 2020 09:07:49 +0100
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.3.1

On 23.11.20 09:05, Thomas Huth wrote:
> On 23/11/2020 08.39, Christian Borntraeger wrote:
>> On 20.11.20 17:01, Eric Farman wrote:
>>> A Linux binary will have the string "S390EP" at address 0x10008,
>>> which is important in getting the guest up off the ground. In the
>>> case of a reboot (specifically chreipl going to a new device),
>>> we should defer to the PSW at address zero for the new config,
>>> which will re-write "S390EP" from the new image.
>>> Let's clear it out at this point so that a reipl to, say, a DASD
>>> passthrough device drives the IPL path from scratch without disrupting
>>> disrupting the order of operations for other boots.
>>> Rather than hardcoding the address of this magic (again), let's
>>> define it somewhere so that the two users are visibly related.
>> Hmmm, this might have side effects, e.g. if you do something like a kdump
>> or kexec to a non-Linux binary that happens to have code at 0x10008, no?
> Do these scenarios really go through the s390-ccw bios again, or do they
> rather bypass the bios and jump directly into the new kernel?

Right they jump directly into the new kernel. So this patch could actually
be "good enough" for 5.2 as is?

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