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

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Date:   Fri, 17 Sep 2021 13:50:54 -0400
From:   Boris Ostrovsky <boris.ostrovsky@...cle.com>
To:     Juergen Gross <jgross@...e.com>, 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>
Subject: Re: [PATCH] xen/x86: fix PV trap handling on secondary processors


On 9/17/21 3:24 AM, Juergen Gross wrote:
> 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.


Yes, that would be my preference. No preference on where to set the sentinel.


Thanks.

-boris


>>>
>>> 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