linux-kernel - Re: [RFC PATCH 09/13] x86/uintr: Introduce vector registration and uintr

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Date:   Tue, 28 Sep 2021 13:40:30 -0700
From:   Sohil Mehta <sohil.mehta@...el.com>
To:     Thomas Gleixner <tglx@...utronix.de>, <x86@...nel.org>
CC:     Tony Luck <tony.luck@...el.com>,
        Dave Hansen <dave.hansen@...el.com>,
        "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 09/13] x86/uintr: Introduce vector registration and
 uintr_fd syscall

On 9/24/2021 3:33 AM, Thomas Gleixner wrote:
> If this ever comes back in some form, then I pretty please want the life
> time rules of this documented properly.

I'll document the life time rules for the UPID, vector and UITT next 
time. I realize now that they are quite convoluted in the current 
implementation.

I'll also fix the concurrency and serialization issues that you 
mentioned in this patch and the next one.


>
>> +	ret = task_work_add(r_info->upid_ctx->task, &r_info->twork, true);
> Care to look at the type of the third argument of task_work_add()?

Ah! I didn't realize the third argument changed a long time back.


>
>> +/*
>> + * sys_uintr_create_fd - Create a uintr_fd for the registered interrupt vector.
> So this creates a file descriptor for a vector which is already
> allocated and then it calls do_uintr_register_vector() which allocates
> the vector?

The syscall comment is misleading. Will fix it.

Vector allocation happens in userspace. The application is only expected 
to register the vector.

This syscall only creates an FD abstraction for the vector that is 
*being* registered.

>> + */
>> +SYSCALL_DEFINE2(uintr_create_fd, u64, vector, unsigned int, flags)
>> +{

Thanks,

Sohil