linux-kernel - Re: [PATCH v3] xen: get rid of paravirt op adjust_exception

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Date:   Mon, 7 Aug 2017 19:51:27 -0700
From:   Andy Lutomirski <luto@...capital.net>
To:     Boris Ostrovsky <boris.ostrovsky@...cle.com>
Cc:     Juergen Gross <jgross@...e.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "xen-devel@...ts.xenproject.org" <xen-devel@...ts.xenproject.org>,
        X86 ML <x86@...nel.org>, "H. Peter Anvin" <hpa@...or.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>
Subject: Re: [PATCH v3] xen: get rid of paravirt op adjust_exception_frame

On Mon, Aug 7, 2017 at 1:56 PM, Boris Ostrovsky
<boris.ostrovsky@...cle.com> wrote:
>
>> diff --git a/arch/x86/xen/enlighten_pv.c b/arch/x86/xen/enlighten_pv.c
>> index 811e4ddb3f37..a3dcd83187ce 100644
>> --- a/arch/x86/xen/enlighten_pv.c
>> +++ b/arch/x86/xen/enlighten_pv.c
>> @@ -579,6 +579,71 @@ static void xen_write_ldt_entry(struct desc_struct *dt, int entrynum,
>>       preempt_enable();
>>  }
>>
>> +#ifdef CONFIG_X86_64
>> +static struct {
>> +     void (*orig)(void);
>> +     void (*xen)(void);
>> +     bool ist_okay;
>> +     bool handle;
>> +} trap_array[] = {
>> +     { debug, xen_xendebug, true, true },
>> +     { int3, xen_xenint3, true, true },
>> +     { double_fault, xen_double_fault, true, false },
>
> Is it really worth adding 'handle' member to the structure because of a
> single special case? We don't expect to ever have another such vector.
>
> (TBH, I think current implementation of cvt_gate_to_trap() is clearer,
> even if it is not as general as what is in this patch. I know that Andy
> disagrees).

I have no real opinion either way.  I just think it's nicer to put it
in cvt_gate_to_trap() instead of the the traps.c setup code.

--Andy