linux-kernel - Re: Sleeping in user

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Message-ID: <691acc7f-6ce1-69da-d56d-4d3c0fdad9ab@zytor.com>
Date:   Tue, 27 Nov 2018 11:05:40 -0800
From:   "H. Peter Anvin" <hpa@...or.com>
To:     Julien Thierry <julien.thierry@....com>,
        Russell King - ARM Linux <linux@...linux.org.uk>
Cc:     Ingo Molnar <mingo@...hat.com>,
        LKML <linux-kernel@...r.kernel.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will.deacon@....com>,
        James Morse <james.morse@....com>
Subject: Re: Sleeping in user_access section

On 11/23/18 3:57 AM, Julien Thierry wrote:
> 
> On x86, the EFLAGS.AC bit is also saved upon exception and I think it is
> cleared upon exception entry so there is implicit exit from the
> user_access mode when taking exception/interrupt.
> 

No, it is restored, not cleared.

In summary: on exceptions, user_access regions are suspended, and on
return the user_access status is resumed.

However, explicitly calling sleeping functions is not supported.

	-hpa