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Subject: Re: [PATCH v4 07/10] x86/xsaves: Fix PTRACE frames for XSAVES
To: Yu-cheng Yu <yu-cheng.yu@intel.com>
References: <cover.1457038929.git.yu-cheng.yu@intel.com>
 <46ff4951eef7e9ad30b25df401fa536a5bc9100b.1457038929.git.yu-cheng.yu@intel.com>
 <5723C33E.1020303@linux.intel.com> <20160429223050.GA15714@test-lenovo>
Cc: x86@kernel.org, "H. Peter Anvin" <hpa@zytor.com>,
        Thomas Gleixner <tglx@linutronix.de>, Ingo Molnar <mingo@redhat.com>,
        linux-kernel@vger.kernel.org, Andy Lutomirski <luto@kernel.org>,
        Borislav Petkov <bp@suse.de>,
        Sai Praneeth Prakhya <sai.praneeth.prakhya@intel.com>,
        "Ravi V. Shankar" <ravi.v.shankar@intel.com>,
        Fenghua Yu <fenghua.yu@intel.com>
From: Dave Hansen <dave.hansen@linux.intel.com>
Message-ID: <5723E1DC.6040207@linux.intel.com>
Date: Fri, 29 Apr 2016 15:36:12 -0700
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On 04/29/2016 03:30 PM, Yu-cheng Yu wrote:
> On Fri, Apr 29, 2016 at 01:25:34PM -0700, Dave Hansen wrote:
>> On 03/04/2016 10:12 AM, Yu-cheng Yu wrote:
>>> +	for (i = 0; i < XFEATURE_MAX; i++) {
>>> +		/*
>>> +		 * Copy only in-use xstates.
>>> +		 */
>>> +		if (((header.xfeatures >> i) & 1) && xfeature_enabled(i)) {
>>> +			void *src = get_xsave_addr_no_check(xsave, i);
>>
>> How could a bit in header.xfeatures get set if it is not set in
>> xfeature_enabled() aka xfeatures_mask aka XCR0?
> 
> Do you mean, we should test xfeature_enabled(i) first, like,
> 
> 	if (xfeature_enabled(i) && ((header.xfeatures >> i) & 1)) ?
> 
> The result will be the same, like you said, if XCR0[i] is not set,
> hader.xfeatures[i] cannot be set.  But if XCR0[i] is set,
> header.xfeatures[i] can be cleared. 

I think the xfeature_enabled(i) is probably redundant.  Does it serve
any actual purpose?