linux-kernel - Re: [RFC PATCH 10/13] x86/uintr: Introduce user IPI sender syscalls

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Date:   Tue, 28 Sep 2021 11:01:54 -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 10/13] x86/uintr: Introduce user IPI sender syscalls

On 9/23/2021 5:28 AM, Greg KH wrote:
> On Mon, Sep 13, 2021 at 01:01:29PM -0700, Sohil Mehta wrote:
>> +/* User Interrupt Target Table Entry (UITTE) */
>> +struct uintr_uitt_entry {
>> +	u8	valid;			/* bit 0: valid, bit 1-7: reserved */
> Do you check that the other bits are set to 0?

I don't have a check but kzalloc() in alloc_uitt() should set it to 0.

>> +	u8	user_vec;
>> +	u8	reserved[6];
> What is this reserved for?

This is hardware defined structure as well. I should probably mention 
this it in the comment above.

>> +	u64	target_upid_addr;
> If this is a pointer, why not say it is a pointer?

I used a u64 to get the size and alignment of this structure as required 
by the hardware. I wasn't sure if using a struct upid * would complicate 
that.

Also this field is never used as a pointer by the kernel. It is only 
used to program an entry that is read by the hardware.

Is this reasonable or would you still prefer a pointer?


>> +} __packed __aligned(16);
>> +
>> +struct uintr_uitt_ctx {
>> +	struct uintr_uitt_entry *uitt;
>> +	/* Protect UITT */
>> +	spinlock_t uitt_lock;
>> +	refcount_t refs;
> Again, a kref please.

Will do.

Thanks,

Sohil