Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
IronPort-SDR: M+pd+nCG5c7YBvlqyOv7H32KokVtfkeJ4uTscnzMRMJ54OgEf+dBtHkCuGxD4RJOK6QQ3mXYMs
 aulZPyJQ1q3w==
IronPort-SDR: 5YUFgyEOmHp/+MWrN7JiWpc6CggC+fZhcCS9g7MCs9puzXcGvQ41vXaUw9ODLfEgKGWFXk1e8n
 qEK6gUaHOmZg==
Subject: Re: [PATCH v4 14/22] x86/fpu/xstate: Expand the xstate buffer on the
 first use of dynamic user state
To:     "Bae, Chang Seok" <chang.seok.bae@intel.com>
Cc:     Len Brown <lenb@kernel.org>, Andy Lutomirski <luto@kernel.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Borislav Petkov <bp@suse.de>, Ingo Molnar <mingo@kernel.org>,
        X86 ML <x86@kernel.org>, "Brown, Len" <len.brown@intel.com>,
        "Hansen, Dave" <dave.hansen@intel.com>,
        "Liu, Jing2" <jing2.liu@intel.com>,
        "Shankar, Ravi V" <ravi.v.shankar@intel.com>,
        LKML <linux-kernel@vger.kernel.org>
References: <20210221185637.19281-1-chang.seok.bae@intel.com>
 <20210221185637.19281-15-chang.seok.bae@intel.com>
 <87o8fda2ye.fsf@nanos.tec.linutronix.de>
 <CALCETrVaCmG4jzLCSuy7WYP2K7r-MVZntfugWa8HiVxQ7LpF_A@mail.gmail.com>
 <CAJvTdKmz7aePcpi4i+d3vnqLuNAJEuJCjpGDv5WTYcSUfuxoDg@mail.gmail.com>
 <6ed9d725-a6cb-4147-9c8a-2fe240e4bb10@linux.intel.com>
 <CAJvTdKm_uP-RqoprWWatg725WZOm3T-BHZU8S08dpWe2=1apGw@mail.gmail.com>
 <87fb254f-a904-303e-daee-c9a3e9bf13b7@linux.intel.com>
 <A2F31E33-4F15-431B-8407-438750186895@intel.com>
From:   "Liu, Jing2" <jing2.liu@linux.intel.com>
Message-ID: <84047b4a-48e3-6efc-643a-06cfcc0630cc@linux.intel.com>
Date:   Thu, 25 Mar 2021 15:26:08 +0800
User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:78.0) Gecko/20100101
 Thunderbird/78.6.0
MIME-Version: 1.0
In-Reply-To: <A2F31E33-4F15-431B-8407-438750186895@intel.com>
Content-Type: text/plain; charset=utf-8; format=flowed
Content-Transfer-Encoding: 7bit
Content-Language: en-US
Precedence: bulk


>>> For AMX, we must still reserve the space, but we are not going to write zeros
>>> for clean state.  We so this in software by checking XINUSE=0, and clearing
>>> the xstate_bf for the XSAVE.  As a result, for XINUSE=0, we can skip
>>> writing the zeros, even though we can't compress the space.
>> So my understanding is that clearing xstate_bv will not help prevent saving
>> zeros, but only not masking EDX:EAX, since the following logic. Not sure if
>> this is just what you mean. :)
> FWIW, PATCH21 [1] uses the instruction mask to skip writing zeros on sigframe.
> Then, XSAVE will clear the xstate_bv for the xtile data state bit.
>
> [1] https://lore.kernel.org/lkml/20210221185637.19281-22-chang.seok.bae@intel.com/
Yes, no mask in EDX:EAX works in such case. Thanks for pointing out the 
patch.

BRs,
Jing
>
> Thanks,
> Chang