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Date: Tue, 1 Mar 2016 16:48:34 -0800
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 v3 9/9] x86/xsaves: Re-enable XSAVES
Message-ID: <20160302004834.GA30942@test-lenovo>
References: <cover.1456524359.git.yu-cheng.yu@intel.com>
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On Tue, Mar 01, 2016 at 04:45:41PM -0800, Dave Hansen wrote:
> >>> +	WARN_ONCE((xfeatures_mask & XFEATURE_MASK_SUPERVISOR),
> >>> +		"x86/fpu: XSAVES supervisor states are not yet implemented.\n");
> >>> +
> >>>  	cr4_set_bits(X86_CR4_OSXSAVE);
> >>>  	xsetbv(XCR_XFEATURE_ENABLED_MASK, xfeatures_mask);
> >>>  }
> >>
> >> Let's also do a:
> >>
> >> 	xfeatures_mask &= ~XFEATURE_MASK_SUPERVISOR;
> >>
> >> Otherwise, we have a broken system at the moment.
> >>
> > Currently, if anyone sets any supervisor state in xfeatures_mask, the
> > kernel prints out the warning then goes into a protection fault.
> > That is a very strong indication to the user. Do we want to mute it? 
> 
> By "goes into a protection fault", do you mean that it doesn't boot?
> 
> I'd just rather we put the kernel in a known-safe configuration (masking
> supervisor state out of xfeatures_mask) rather than rely on the general
> protection fault continuing to be generated by whatever is generating it.
> 
Ok.

Yu-cheng