linux-kernel - Re: [v2 5/7] x86: Add emulation code for UMIP instructions

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Date:   Fri, 30 Dec 2016 18:07:44 -0800
From:   Andy Lutomirski <luto@...capital.net>
To:     Ricardo Neri <ricardo.neri-calderon@...ux.intel.com>
Cc:     Ingo Molnar <mingo@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Borislav Petkov <bp@...e.de>,
        Andy Lutomirski <luto@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        X86 ML <x86@...nel.org>, linux-msdos@...r.kernel.org,
        wine-devel@...ehq.org, Andrew Morton <akpm@...ux-foundation.org>,
        "H . Peter Anvin" <hpa@...or.com>, Brian Gerst <brgerst@...il.com>,
        Chen Yucong <slaoub@...il.com>,
        Chris Metcalf <cmetcalf@...lanox.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Fenghua Yu <fenghua.yu@...el.com>,
        Huang Rui <ray.huang@....com>, Jiri Slaby <jslaby@...e.cz>,
        Jonathan Corbet <corbet@....net>,
        "Michael S . Tsirkin" <mst@...hat.com>,
        Paul Gortmaker <paul.gortmaker@...driver.com>,
        "Ravi V . Shankar" <ravi.v.shankar@...el.com>,
        Shuah Khan <shuah@...nel.org>,
        Vlastimil Babka <vbabka@...e.cz>,
        Tony Luck <tony.luck@...el.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        "Liang Z . Li" <liang.z.li@...el.com>,
        Alexandre Julliard <julliard@...ehq.org>,
        Stas Sergeev <stsp@...t.ru>
Subject: Re: [v2 5/7] x86: Add emulation code for UMIP instructions

On Thu, Dec 29, 2016 at 9:23 PM, Ricardo Neri
<ricardo.neri-calderon@...ux.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