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From: Linus Torvalds <torvalds@linux-foundation.org>
Date: Mon, 30 Oct 2017 10:46:31 -0700
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Subject: Re: [ghes_copy_tofrom_phys] BUG: sleeping function called from
 invalid context at mm/page_alloc.c:4150
To: Borislav Petkov <bp@suse.de>, Len Brown <lenb@kernel.org>,
        Tony Luck <tony.luck@intel.com>
Cc: Fengguang Wu <fengguang.wu@intel.com>,
        Tyler Baicar <tbaicar@codeaurora.org>,
        Huang Ying <ying.huang@intel.com>,
        Chen Gong <gong.chen@linux.intel.com>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Will Deacon <will.deacon@arm.com>,
        "Rafael J. Wysocki" <rjw@rjwysocki.net>,
        Linux ACPI <linux-acpi@vger.kernel.org>
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On Mon, Oct 30, 2017 at 10:20 AM, Linus Torvalds
<torvalds@linux-foundation.org> wrote:
>
> I will add a "might_sleep()" to ioremap_page_range() itself, so that
> we get this warning more reliably and much eailer. Right now it has
> been hidden by the fact that most of the time the time the page tables
> may be already allocated, but even then it's broken.

Done. It doesn't report anything for me, so _hopefully_ the GHES
driver is the only one that does games like this. See commit
b39ab98e2f47 ("Mark 'ioremap_page_range()' as possibly sleeping").

So now it should hopefully warn about this bad usage of page remapping
reliably, at least if you have CONFIG_DEBUG_ATOMIC_SLEEP enabled.

Can somebody who has a working GHES setup (although Borislav seems to
think no such thing exists) verify?

This obviously won't _fix_ anything, but at least it should make it
clear it's not that recent change that broke things - that just
happened to expose it. And hopefully somebody who knows that driver
will do the proper fixmap thing (or just ioremap once at probe time,
rather than at run-time).

                    Linus