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From: Andy Lutomirski <luto@amacapital.net>
Date: Fri, 30 Dec 2016 18:07:44 -0800
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Subject: Re: [v2 5/7] x86: Add emulation code for UMIP instructions
To: Ricardo Neri <ricardo.neri-calderon@linux.intel.com>
Cc: Ingo Molnar <mingo@redhat.com>, Thomas Gleixner <tglx@linutronix.de>,
        Borislav Petkov <bp@suse.de>, Andy Lutomirski <luto@kernel.org>,
        Peter Zijlstra <peterz@infradead.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        X86 ML <x86@kernel.org>, linux-msdos@vger.kernel.org,
        wine-devel@winehq.org, Andrew Morton <akpm@linux-foundation.org>,
        "H . Peter Anvin" <hpa@zytor.com>, Brian Gerst <brgerst@gmail.com>,
        Chen Yucong <slaoub@gmail.com>, Chris Metcalf <cmetcalf@mellanox.com>,
        Dave Hansen <dave.hansen@linux.intel.com>,
        Fenghua Yu <fenghua.yu@intel.com>, Huang Rui <ray.huang@amd.com>,
        Jiri Slaby <jslaby@suse.cz>, Jonathan Corbet <corbet@lwn.net>,
        "Michael S . Tsirkin" <mst@redhat.com>,
        Paul Gortmaker <paul.gortmaker@windriver.com>,
        "Ravi V . Shankar" <ravi.v.shankar@intel.com>,
        Shuah Khan <shuah@kernel.org>, Vlastimil Babka <vbabka@suse.cz>,
        Tony Luck <tony.luck@intel.com>, Paolo Bonzini <pbonzini@redhat.com>,
        "Liang Z . Li" <liang.z.li@intel.com>,
        Alexandre Julliard <julliard@winehq.org>, Stas Sergeev <stsp@list.ru>
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On Thu, Dec 29, 2016 at 9:23 PM, Ricardo Neri
<ricardo.neri-calderon@linux.intel.com> wrote:
> On Tue, 2016-12-27 at 16:48 -0800, Andy Lutomirski wrote:
>>
>> >> > +               if (nr_copied  > 0)
>> >> > +                       return -EFAULT;
>> >>
>> >> This should be the only EFAULT case.
>> > Should this be EFAULT event if the caller cares only about successful
>> > (return 0) vs failed (return non-0) emulation?
>>
>> In theory this particular error would be a page fault not a general
>> protection fault (in the UMIP off case).  If you were emulating it
>> extra carefully, you could change the signal accordingly.  But, as I
>> said, I really doubt this matters.
>
> If simple enough and for the sake of accuracy, I could try to issue the
> page fault. It seems to me that this entitles calling
> force_sig_info_fault in this particular case as opposed to the
> force_sig_info(SIGSEGV, SEND_SIG_PRIV, tsk) that do_general_protection
> calls.

Sure.  You could even do it by sending the signal in the emulation
code and returning true.

--Andy