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

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Date:   Tue, 28 Sep 2021 06:39:29 +0200
From:   Greg KH <gregkh@...uxfoundation.org>
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 06/13] x86/uintr: Introduce uintr receiver syscalls

On Mon, Sep 27, 2021 at 04:20:25PM -0700, Sohil Mehta wrote:
> 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).

Then those values must be set to 0, right?  I think I missed the part of
the code that set them, hopefully it's somewhere...

thanks,

greg k-h