linux-kernel - Re: [RFC PATCH 06/13] x86/uintr: Introduce uintr receiver syscalls

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Date:   Mon, 27 Sep 2021 16:20:25 -0700
From:   Sohil Mehta <sohil.mehta@...el.com>
To:     Greg KH <gregkh@...uxfoundation.org>
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 06/13] x86/uintr: Introduce uintr receiver syscalls

On 9/23/2021 5:26 AM, Greg KH wrote:
> On Mon, Sep 13, 2021 at 01:01:25PM -0700, Sohil Mehta wrote:
>> +
>> +/* User Posted Interrupt Descriptor (UPID) */
>> +struct uintr_upid {
>> +	struct {
>> +		u8 status;	/* bit 0: ON, bit 1: SN, bit 2-7: reserved */
>> +		u8 reserved1;	/* Reserved */
>> +		u8 nv;		/* Notification vector */
>> +		u8 reserved2;	/* Reserved */
> What are these "reserved" for?


The UPID is an architectural data structure defined by the hardware. The 
reserved fields are defined by the hardware (likely to keep the 
structure size as 16 bytes).


>
>> +struct uintr_upid_ctx {
>> +	struct uintr_upid *upid;
>> +	refcount_t refs;
> Please use a kref for this and do not roll your own for no good reason.

Sure. Will do.