linux-kernel - Re: [PATCH v10 05/28] x86/fpu/xstate: Add a new variable to indicate dynamic user states

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Date:   Sun, 3 Oct 2021 22:35:51 +0000
From:   "Bae, Chang Seok" <chang.seok.bae@...el.com>
To:     Thomas Gleixner <tglx@...utronix.de>
CC:     "bp@...e.de" <bp@...e.de>, "Lutomirski, Andy" <luto@...nel.org>,
        "mingo@...nel.org" <mingo@...nel.org>,
        "x86@...nel.org" <x86@...nel.org>,
        "Brown, Len" <len.brown@...el.com>,
        "lenb@...nel.org" <lenb@...nel.org>,
        "Hansen, Dave" <dave.hansen@...el.com>,
        "Macieira, Thiago" <thiago.macieira@...el.com>,
        "Liu, Jing2" <jing2.liu@...el.com>,
        "Shankar, Ravi V" <ravi.v.shankar@...el.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v10 05/28] x86/fpu/xstate: Add a new variable to indicate
 dynamic user states

On Oct 1, 2021, at 06:16, Thomas Gleixner <tglx@...utronix.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.

But let me move it to patch13 [1] where the variable is updated.

Thanks,
Chang

[1] https://lore.kernel.org/lkml/20210825155413.19673-14-chang.seok.bae@intel.com/