Date: Fri, 29 Apr 2016 15:30:50 -0700
From: Yu-cheng Yu <yu-cheng.yu@intel.com>
To: Dave Hansen <dave.hansen@linux.intel.com>
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>
Subject: Re: [PATCH v4 07/10] x86/xsaves: Fix PTRACE frames for XSAVES
Message-ID: <20160429223050.GA15714@test-lenovo>
References: <cover.1457038929.git.yu-cheng.yu@intel.com>
 <46ff4951eef7e9ad30b25df401fa536a5bc9100b.1457038929.git.yu-cheng.yu@intel.com>
 <5723C33E.1020303@linux.intel.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <5723C33E.1020303@linux.intel.com>
User-Agent: Mutt/1.5.21 (2010-09-15)
Sender: linux-kernel-owner@vger.kernel.org
Content-Length: 947
Lines: 26

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. 

> 
> If a caller tries to pass a non-enabled xfeature in, we appear to just
> silently drop it and return success.  Is that really what we want to do
> or do we want to error out?

Let it fail.  I will chage it.