linux-kernel - Re: [RFC PATCH 04/13] x86/fpu/xstate: Enumerate User Interrupts supervisor state

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Date:   Fri, 24 Sep 2021 00:34:04 +0200
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Sohil Mehta <sohil.mehta@...el.com>, x86@...nel.org
Cc:     Sohil Mehta <sohil.mehta@...el.com>,
        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 04/13] x86/fpu/xstate: Enumerate User Interrupts
 supervisor state

On Mon, Sep 13 2021 at 13:01, Sohil Mehta wrote:
> Enable xstate supervisor support for User Interrupts by default.

What means enabled by default? It's enabled when available and not
disabled on the command line.

> The user interrupt state for a task consists of the MSR state and the
> User Interrupt Flag (UIF) value. XSAVES and XRSTORS handle saving and
> restoring both of these states.
>
> <The supervisor XSTATE code might be reworked based on issues reported
> in the past. The Uintr context switching code would also need rework and
> additional testing in that regard.>

What? Which issues were reported and if they have been reported then how
is the provided code correct?

> +/*
> + * State component 14 is supervisor state used for User Interrupts state.
> + * The size of this state is 48 bytes
> + */
> +struct uintr_state {
> +	u64 handler;
> +	u64 stack_adjust;
> +	u32 uitt_size;
> +	u8  uinv;
> +	u8  pad1;
> +	u8  pad2;
> +	u8  uif_pad3;		/* bit 7 - UIF, bits 6:0 - reserved */

Please do not use tail comments. Also what kind of name is uif_pad3?
Bitfields exist for a reason.

Aside of that please use tabs to seperate type and name.

> +	u64 upid_addr;
> +	u64 uirr;
> +	u64 uitt_addr;
> +} __packed;
> +

Thanks,

        tglx