linux-kernel - Re: [PATCH 2/2] s390: mm: Fix secure storage access exception handling

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Message-ID: <221ce6ab-4630-473d-a49f-150ac8c573d6@de.ibm.com>
Date:   Wed, 20 Jan 2021 15:39:14 +0100
From:   Christian Borntraeger <borntraeger@...ibm.com>
To:     Heiko Carstens <hca@...ux.ibm.com>
Cc:     Janosch Frank <frankja@...ux.ibm.com>,
        linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
        thuth@...hat.com, david@...hat.com, imbrenda@...ux.ibm.com,
        cohuck@...hat.com, linux-s390@...r.kernel.org, gor@...ux.ibm.com,
        mihajlov@...ux.ibm.com
Subject: Re: [PATCH 2/2] s390: mm: Fix secure storage access exception
 handling



On 20.01.21 14:42, Heiko Carstens wrote:
> On Tue, Jan 19, 2021 at 11:25:01AM +0100, Christian Borntraeger wrote:
>>> +		if (user_mode(regs)) {
>>> +			send_sig(SIGSEGV, current, 0);
>>> +			return;
>>> +		} else
>>> +			panic("Unexpected PGM 0x3d with TEID bit 61=0");
>>
>> use BUG instead of panic? That would kill this process, but it allows
>> people to maybe save unaffected data.
> 
> It would kill the process, and most likely lead to deadlock'ed
> system. But with all the "good" debug information being lost, which
> wouldn't be the case with panic().
> I really don't think this is a good idea.
> 

My understanding is that Linus hates panic for anything that might be able
to continue to run. With BUG the admin can decide via panic_on_oops if
debugging data or runtime data is more important. But mm is more on your
side, so if you insist on panic we can keep it.