linux-kernel - Re: [PATCH v2 1/4] usb: early: Avoid using DbC if already enabled

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Message-ID: <55325db1-b086-fc81-9117-6560c4914a12@gmail.com>
Date:   Mon, 17 May 2021 08:24:41 -0600
From:   Connor Davis <connojdavis@...il.com>
To:     Jan Beulich <jbeulich@...e.com>
Cc:     Jann Horn <jannh@...gle.com>, Lee Jones <lee.jones@...aro.org>,
        Chunfeng Yun <chunfeng.yun@...iatek.com>,
        linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org,
        xen-devel@...ts.xenproject.org,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Subject: Re: [PATCH v2 1/4] usb: early: Avoid using DbC if already enabled


On 5/17/21 8:13 AM, Jan Beulich wrote:
> On 17.05.2021 15:48, Connor Davis wrote:
>> On 5/17/21 3:32 AM, Jan Beulich wrote:
>>> On 14.05.2021 02:56, Connor Davis wrote:
>>>> Check if the debug capability is enabled in early_xdbc_parse_parameter,
>>>> and if it is, return with an error. This avoids collisions with whatever
>>>> enabled the DbC prior to linux starting.
>>> Doesn't this go too far and prevent use even if firmware (perhaps
>>> mistakenly) left it enabled?
>> Yes, but how is one supposed to distinguish the broken firmware and
>> non-broken
>>
>> firmware cases?
> Well, a first step might be to only check if running virtualized.
> And then if your running virtualized, there might be a way to
> inquire the hypervisor?

Right, but if it was enabled by something other than a hypervisor,

or you're not running virtualized, how do you distinguish then? IMO

the proper thing to do in any case is to simply not use the DbC in linux.

Thanks,

Connor