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Subject: Re: [PATCH] xen/x86: fix PV trap handling on secondary processors
To:     Jan Beulich <jbeulich@suse.com>
Cc:     Stefano Stabellini <sstabellini@kernel.org>,
        lkml <linux-kernel@vger.kernel.org>,
        "xen-devel@lists.xenproject.org" <xen-devel@lists.xenproject.org>,
        Boris Ostrovsky <boris.ostrovsky@oracle.com>
References: <34898e9c-5883-a978-98ee-b81b22d8caed@suse.com>
 <823f4ef4-f9e5-68cb-d6e9-d079483c1e21@oracle.com>
 <0afce6e8-3c8a-e5ae-cd54-0fd598276506@suse.com>
 <62ccf5b7-b903-e604-d113-67c7633278cd@suse.com>
 <2c4549c8-bdeb-3584-95c4-7076b7cf79bb@suse.com>
From:   Juergen Gross <jgross@suse.com>
Message-ID: <35835650-bbbb-7dbd-061b-693f39f9453e@suse.com>
Date:   Fri, 17 Sep 2021 09:24:34 +0200
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From: Juergen Gross <jgross@suse.com>
To: Jan Beulich <jbeulich@suse.com>
Cc: Stefano Stabellini <sstabellini@kernel.org>,
 lkml <linux-kernel@vger.kernel.org>,
 "xen-devel@lists.xenproject.org" <xen-devel@lists.xenproject.org>,
 Boris Ostrovsky <boris.ostrovsky@oracle.com>
Message-ID: <35835650-bbbb-7dbd-061b-693f39f9453e@suse.com>
Subject: Re: [PATCH] xen/x86: fix PV trap handling on secondary processors
References: <34898e9c-5883-a978-98ee-b81b22d8caed@suse.com>
 <823f4ef4-f9e5-68cb-d6e9-d079483c1e21@oracle.com>
 <0afce6e8-3c8a-e5ae-cd54-0fd598276506@suse.com>
 <62ccf5b7-b903-e604-d113-67c7633278cd@suse.com>
 <2c4549c8-bdeb-3584-95c4-7076b7cf79bb@suse.com>
In-Reply-To: <2c4549c8-bdeb-3584-95c4-7076b7cf79bb@suse.com>

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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 =3D this_cpu_ptr(&idt_desc);
>>>>> +	unsigned i, count =3D (desc->size + 1) / sizeof(gate_desc);
>>>>>   =20
>>>>> -	xen_convert_trap_info(desc, traps);
>>>>
>>>>
>>>> Can you instead add a boolean parameter to xen_convert_trap_info() t=
o indicate whether to skip empty entries? That will avoid (almost) duplic=
ating 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 th=
e
>> new parameter and extending the if statement in xen_convert_trap_info(=
)
>> to increment out always if no entry is to be skipped.
>=20
> 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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