linux-kernel - Re: [PATCH] xen/x86: fix PV trap handling on secondary processors

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Date:   Fri, 17 Sep 2021 09:24:34 +0200
From:   Juergen Gross <jgross@...e.com>
To:     Jan Beulich <jbeulich@...e.com>
Cc:     Stefano Stabellini <sstabellini@...nel.org>,
        lkml <linux-kernel@...r.kernel.org>,
        "xen-devel@...ts.xenproject.org" <xen-devel@...ts.xenproject.org>,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>
Subject: Re: [PATCH] xen/x86: fix PV trap handling on secondary processors

On 17.09.21 08:50, Jan Beulich wrote:
> On 17.09.2021 08:47, Juergen Gross wrote:
>> On 17.09.21 08:40, Jan Beulich wrote:
>>> On 17.09.2021 03:34, Boris Ostrovsky wrote:
>>>>
>>>> On 9/16/21 11:04 AM, Jan Beulich wrote:
>>>>>    {
>>>>>    	const struct desc_ptr *desc = this_cpu_ptr(&idt_desc);
>>>>> +	unsigned i, count = (desc->size + 1) / sizeof(gate_desc);
>>>>>    
>>>>> -	xen_convert_trap_info(desc, traps);
>>>>
>>>>
>>>> Can you instead add a boolean parameter to xen_convert_trap_info() to indicate whether to skip empty entries? That will avoid (almost) duplicating the code.
>>>
>>> I can, sure, but I specifically didn't, as the result is going to be less
>>> readable imo. Instead I was considering to fold xen_convert_trap_info()
>>> into its only remaining caller. Yet if you're convinced adding the
>>> parameter is the way to do, I will go that route. But please confirm.
>>
>> I don't think the result will be very hard to read. All you need is the
>> new parameter and extending the if statement in xen_convert_trap_info()
>> to increment out always if no entry is to be skipped.
> 
> And skip writing the sentinel.

Maybe it would be even better then to let xen_convert_trap_info() return
the number of entries written and to write the sentinel in
xen_load_idt() instead, as this is the only place where it is needed.


Juergen

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