linux-kernel - Re: [PATCH] s390/mm: Fix in_atomic() handling in do_secure_storage

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Message-ID: <408922a2-ec1a-4e60-841a-90714a3310de@linux.ibm.com>
Date: Thu, 5 Jun 2025 11:06:29 +0200
From: Christian Borntraeger <borntraeger@...ux.ibm.com>
To: Alexander Gordeev <agordeev@...ux.ibm.com>,
        Claudio Imbrenda <imbrenda@...ux.ibm.com>
Cc: Heiko Carstens <hca@...ux.ibm.com>, Janosch Frank
 <frankja@...ux.ibm.com>,
        David Hildenbrand <david@...hat.com>,
        Sven Schnelle <svens@...ux.ibm.com>, Vasily Gorbik <gor@...ux.ibm.com>,
        kvm@...r.kernel.org, linux-s390@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] s390/mm: Fix in_atomic() handling in
 do_secure_storage_access()

Am 05.06.25 um 11:04 schrieb Alexander Gordeev:
> On Wed, Jun 04, 2025 at 07:40:43PM +0200, Claudio Imbrenda wrote:
>>>>> This could trigger WARN_ON_ONCE() in handle_fault_error_nolock():
>>>>>
>>>>> 		if (WARN_ON_ONCE(!si_code))
>>>>> 			si_code = SEGV_MAPERR;
>>>>>
>>>>> Would this warning be justified in this case (aka user_mode(regs) ==
>>>>> true)?
>>>>
>>>> I think so, because if we are in usermode, we should never trigger
>>>> faulthandler_disabled()
>>>
>>> I think I do not get you. We are in a system call and also in_atomic(),
>>> so faulthandler_disabled() is true and handle_fault_error_nolock(regs, 0)
>>> is called (above).
>>
>> what is the psw in regs?
>> is it not the one that was being used when the exception was triggered?
> 
> Hmm, right. I assume is_kernel_fault() returns false not because
> user_mode(regs) is true, but because we access the secondary AS.
> 
> Still, to me it feels wrong to trigger that warning due to a user
> process activity. But anyway:
> 
> Acked-by: Alexander Gordeev <agordeev@...ux.ibm.com>

Can we trigger a WARN from userspace?