linux-kernel - Re: [RFC PATCH 00/13] x86 User Interrupts support

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Date:   Fri, 1 Oct 2021 10:19:03 +0200
From:   Pavel Machek <pavel@....cz>
To:     Sohil Mehta <sohil.mehta@...el.com>
Cc:     x86@...nel.org, Tony Luck <tony.luck@...el.com>,
        Dave Hansen <dave.hansen@...el.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        "H . Peter Anvin" <hpa@...or.com>,
        Andy Lutomirski <luto@...nel.org>,
        Jens Axboe <axboe@...nel.dk>,
        Christian Brauner <christian@...uner.io>,
        Peter Zijlstra <peterz@...radead.org>,
        Shuah Khan <shuah@...nel.org>, Arnd Bergmann <arnd@...db.de>,
        Jonathan Corbet <corbet@....net>,
        Ashok Raj <ashok.raj@...el.com>,
        Jacob Pan <jacob.jun.pan@...ux.intel.com>,
        Gayatri Kammela <gayatri.kammela@...el.com>,
        Zeng Guang <guang.zeng@...el.com>,
        Dan Williams <dan.j.williams@...el.com>,
        Randy E Witt <randy.e.witt@...el.com>,
        Ravi V Shankar <ravi.v.shankar@...el.com>,
        Ramesh Thomas <ramesh.thomas@...el.com>,
        linux-api@...r.kernel.org, linux-arch@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-kselftest@...r.kernel.org
Subject: Re: [RFC PATCH 00/13] x86 User Interrupts support

Hi!

> Instructions
> ------------
> senduipi <index> - send a user IPI to a target task based on the UITT index.
> 
> clui - Mask user interrupts by clearing UIF (User Interrupt Flag).
> 
> stui - Unmask user interrupts by setting UIF.
> 
> testui - Test current value of UIF.
> 
> uiret - return from a user interrupt handler.

Are other CPU vendors allowed to implement compatible instructions?

If not, we should probably have VDSO entries so kernel can abstract
differences between CPUs.

> Untrusted processes
> -------------------
> The current implementation expects only trusted and cooperating processes to
> communicate using user interrupts. Coordination is expected between processes
> for a connection teardown. In situations where coordination doesn't happen
> (say, due to abrupt process exit), the kernel would end up keeping shared
> resources (like UPID) allocated to avoid faults.

Keeping resources allocated after process exit is a no-no.

Best regards,
								Pavel
-- 
http://www.livejournal.com/~pavelmachek

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