linux-kernel - Re: [PATCH 1/4 v8] x86/ioremap: add a function ioremap

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Message-ID: <20180927020647.GH2555@MiWiFi-R3L-srv>
Date:   Thu, 27 Sep 2018 10:06:47 +0800
From:   Baoquan He <bhe@...hat.com>
To:     lijiang <lijiang@...hat.com>
Cc:     linux-kernel@...r.kernel.org, joro@...tes.org, mingo@...hat.com,
        ebiederm@...ssion.com, hpa@...or.com, tglx@...utronix.de,
        Dave Young <dyoung@...hat.com>,
        "Lendacky, Thomas" <thomas.lendacky@....com>,
        kexec@...ts.infradead.org
Subject: Re: [PATCH 1/4 v8] x86/ioremap: add a function ioremap_encrypted()
 to remap kdump old memory

Hi Lianbo,

On 09/26/18 at 05:34pm, lijiang wrote:
> When SME is enabled on AMD machine, the memory is encrypted in the first
> kernel. In this case, SME also needs to be enabled in kdump kernel, and
> we have to remap the old memory with the memory encryption mask.
> 
> Here we only talk about the case that SME is active in the first kernel,
> and only care it's active too in kdump kernel. there are four cases we
> need considered.
> 
> a. dump vmcore
>    It is encrypted in the first kernel, and needs be read out in kdump
>    kernel.
> 
> b. crash notes
>    When dumping vmcore, the people usually need to read the useful
>    information from notes, and the notes is also encrypted.
> 
> c. iommu device table
>    It is allocated by kernel, need fill its pointer into mmio of amd iommu.
>    It's encrypted in the first kernel, need read the old content to analyze
>    and get useful information.
> 
> d. mmio of amd iommu
>    Register reported by amd firmware, it's not RAM, we don't encrypt in
>    both the first kernel and kdump kernel.
> 
> To achieve the goal, the solution is:
> 1. add a new bool parameter "encrypted" to __ioremap_caller()
>    It is a low level function, and check the newly added parameter, if it's
>    true and in kdump kernel, will remap the memory with sme mask.
> 
> 2. add a new function ioremap_encrypted() to explicitly passed in a "true"
>    value for "encrypted".
>    For above a, b, c, we will call ioremap_encrypted();
> 
> 3. adjust all existed ioremap wrapper functions, passed in "false" for
>    encrypted to make them an before.
> 
>    ioremap_encrypted()\
>    ioremap_cache()     |
>    ioremap_prot()      |
>    ioremap_wt()        |->__ioremap_caller()
>    ioremap_wc()        |
>    ioremap_uc()        |
>    ioremap_nocache()  /

Thanks, I think it's better. Since no code change, just patch log
improvement, maybe you can repost a series and carry both Tom and
Joerg's ACK.