linux-kernel - Re: [PATCH 0/2] um: improve UML page fault handling

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Message-ID: <20240105075109.4f0e2785@meshulam.tesarici.cz>
Date: Fri, 5 Jan 2024 07:51:09 +0100
From: Petr Tesařík <petr@...arici.cz>
To: Richard Weinberger <richard@....at>
Cc: Petr Tesarik <petrtesarik@...weicloud.com>, anton ivanov
 <anton.ivanov@...bridgegreys.com>, Johannes Berg
 <johannes@...solutions.net>, linux-um <linux-um@...ts.infradead.org>,
 linux-kernel <linux-kernel@...r.kernel.org>, Roberto Sassu
 <roberto.sassu@...weicloud.com>, Petr Tesarik
 <petr.tesarik1@...wei-partners.com>
Subject: Re: [PATCH 0/2] um: improve UML page fault handling

Helo Richard,

Am Fri, 5 Jan 2024 00:22:11 +0100 (CET)
schrieb Richard Weinberger <richard@....at>:

> ----- Ursprüngliche Mail -----
> > Von: "Petr Tesarik" <petrtesarik@...weicloud.com>
> > An: "richard" <richard@....at>, "anton ivanov" <anton.ivanov@...bridgegreys.com>, "Johannes Berg"
> > <johannes@...solutions.net>, "linux-um" <linux-um@...ts.infradead.org>, "linux-kernel" <linux-kernel@...r.kernel.org>
> > CC: "Roberto Sassu" <roberto.sassu@...weicloud.com>, petr@...arici.cz, "Petr Tesarik"
> > <petr.tesarik1@...wei-partners.com>
> > Gesendet: Freitag, 15. Dezember 2023 13:14:29
> > Betreff: [PATCH 0/2] um: improve UML page fault handling  
> 
> > From: Petr Tesarik <petr.tesarik1@...wei-partners.com>
> > 
> > Improve UML handling of segmentation faults in kernel mode. Although
> > such page faults are generally caused by a kernel bug, it is annoying
> > if they cause an infinite loop, or panic the kernel. More importantly,
> > a robust implementation allows to write KUnit tests for various guard
> > pages, preventing potential kernel self-protection regressions.
> > 
> > Petr Tesarik (2):
> >  um: do not panic on kernel mode faults
> >  um: oops on accessing an non-present page in the vmalloc area  
> 
> I think this is a good thing to have.

Thanks for the feedback.

> For the implementation side, this needs to use the oops_* helpers
> from kernel/panic.c and taint the kernel, etc...

Yes, I did see that coming but wanted to get some confirmation that
it's worth the effort.

> See arch/x86/kernel/dumpstack.c die() and friends.

This implementation also calls die notifiers, but AFAICS different
architectures are not very consistent in their use. Do you also
require die notifiers for the UML implementation?

Petr T