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From:   Zhenzhong Duan <zhenzhong.duan@gmail.com>
Date:   Thu, 5 Nov 2020 10:19:36 +0800
Message-ID: <CAFH1YnO4xas=YnUSYR3MjxRkFPvezHe7Rt4cdgZU4knvvQqzEA@mail.gmail.com>
Subject: Re: [PATCH] iommu/vt-d: remove redundant variable no_platform_optin
To:     Lu Baolu <baolu.lu@linux.intel.com>
Cc:     linux-kernel <linux-kernel@vger.kernel.org>,
        David Woodhouse <dwmw2@infradead.org>,
        Joerg Roedel <joro@8bytes.org>,
        iommu@lists.linux-foundation.org
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Hi Baolu,

On Thu, Nov 5, 2020 at 9:47 AM Lu Baolu <baolu.lu@linux.intel.com> wrote:
>
> Hi Zhenzhong,
>
> On 11/4/20 4:19 PM, Zhenzhong Duan wrote:
> > no_platform_optin is redundant with dmar_disabled and it's only used in
> > platform_optin_force_iommu(), remove it and use dmar_disabled instead.
>
> It's actually not.
>
> If CONFIG_INTEL_IOMMU_DEFAULT_ON is not set, we will get "dmar_disable =
> 1" and "no_platform_optin = 0". In this case, we must force the iommu on
> and set dmar_disable = 0.
>
> The real use case: if a kernel built with [CONFIG_INTEL_IOMMU_DEFAULT_ON
> = n] running on a platform with thunderbolt ports, we must force IOMMU
> on so that the system could be protected from possible malicious
> peripherals.

Thanks for your explanation, clear now and sorry for the noise.

Regards
Zhenzhong