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From:   Thomas Gleixner <tglx@linutronix.de>
To:     "Bae, Chang Seok" <chang.seok.bae@intel.com>
Cc:     "bp@suse.de" <bp@suse.de>, "Lutomirski, Andy" <luto@kernel.org>,
        "mingo@kernel.org" <mingo@kernel.org>,
        "x86@kernel.org" <x86@kernel.org>,
        "Brown, Len" <len.brown@intel.com>,
        "lenb@kernel.org" <lenb@kernel.org>,
        "Hansen, Dave" <dave.hansen@intel.com>,
        "Macieira, Thiago" <thiago.macieira@intel.com>,
        "Liu, Jing2" <jing2.liu@intel.com>,
        "Shankar, Ravi V" <ravi.v.shankar@intel.com>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH v10 05/28] x86/fpu/xstate: Add a new variable to
 indicate dynamic user states
In-Reply-To: <DC2E88A6-4CE8-4F10-B527-081EE147927A@intel.com>
References: <20210825155413.19673-1-chang.seok.bae@intel.com>
 <20210825155413.19673-6-chang.seok.bae@intel.com> <87bl486g1y.ffs@tglx>
 <DC2E88A6-4CE8-4F10-B527-081EE147927A@intel.com>
Date:   Mon, 04 Oct 2021 14:57:39 +0200
Message-ID: <875yudgd6k.ffs@tglx>
MIME-Version: 1.0
Content-Type: text/plain
Precedence: bulk

On Sun, Oct 03 2021 at 22:35, Chang Seok Bae wrote:
> On Oct 1, 2021, at 06:16, Thomas Gleixner <tglx@linutronix.de> wrote:
>> On Wed, Aug 25 2021 at 08:53, Chang S. Bae wrote:
>>> +/*
>>> + * This represents user xstates, a subset of xfeatures_mask_all, saved in a
>>> + * dynamic kernel XSAVE buffer.
>>> + */
>>> +u64 xfeatures_mask_user_dynamic __ro_after_init;
>>> +
>>> static unsigned int xstate_offsets[XFEATURE_MAX] __ro_after_init =
>>> 	{ [ 0 ... XFEATURE_MAX - 1] = -1};
>>> static unsigned int xstate_sizes[XFEATURE_MAX] __ro_after_init =
>>> @@ -709,6 +715,7 @@ static int __init init_xstate_size(void)
>>> static void fpu__init_disable_system_xstate(void)
>>> {
>>> 	xfeatures_mask_all = 0;
>>> +	xfeatures_mask_user_dynamic = 0;
>> 
>> It's zero at boot already, isn't it?
>
> I thought of this as a safety net here when it was introduced.

A safety net for what? The compiler initializing the variable to 4711?