linux-kernel - Re: [PATCH 2/2] efi/esrt: mark ESRT memory region as nomap

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Message-ID: <9e3fa182-0635-108f-590b-6f1966bdabe0@codeaurora.org>
Date:   Mon, 26 Feb 2018 10:06:11 -0500
From:   Tyler Baicar <tbaicar@...eaurora.org>
To:     Ard Biesheuvel <ard.biesheuvel@...aro.org>,
        James Morse <james.morse@....com>,
        AKASHI Takahiro <takahiro.akashi@...aro.org>
Cc:     linux-efi@...r.kernel.org,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Jeff Hugo <jhugo@...eaurora.org>,
        Sameer Goel <sgoel@...eaurora.org>,
        Timur Tabi <timur@...eaurora.org>
Subject: Re: [PATCH 2/2] efi/esrt: mark ESRT memory region as nomap

Hello Ard,


On 2/24/2018 3:03 AM, Ard Biesheuvel wrote:
> Hi Tyler,
>
> On 23 February 2018 at 19:42, Tyler Baicar <tbaicar@...eaurora.org> wrote:
>> The ESRT memory region is being exposed as System RAM in /proc/iomem
>> which is wrong because it cannot be overwritten. This memory is needed
>> for kexec kernels in order to properly initialize ESRT, so if it is
>> overwritten it will cause ESRT failures in the kexec kernel. Mark this
>> region as nomap so that it is not overwritten.
>>
> This is not the right fix. We should only mark regions NOMAP if it is
> uncertain whether the firmware may have a mapping of the same region
> with mismatched attributes. NOMAP regions punch holes in the linear
> region, increasing its TLB footprint significantly, so we should avoid
> them if we can.
Thanks for the explanation, that makes sense.
> This same issue has come up in relation to mapping ACPI tables after
> kexec. This should simply be a matter of ensuring that all
> memblock_reserve()d region appear as such in /proc/iomem rather than
> as 'System RAM'
Do you know why this memory region would be coming up as System RAM rather than 
reserved if we're
calling memblock_reserve() on it in efi_mem_reserve()?

Thanks,
Tyler

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