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From:   Ard Biesheuvel <ardb@kernel.org>
Date:   Thu, 14 Apr 2022 12:22:31 +0200
Message-ID: <CAMj1kXGSStDgj9ABmUaTLnBmpQFksh3wx4tx=mJohum4GQe3Gg@mail.gmail.com>
Subject: Re: [PATCH v2 0/9] introduce mirrored memory support for arm64
To:     Wupeng Ma <mawupeng1@huawei.com>
Cc:     Andrew Morton <akpm@linux-foundation.org>,
        Catalin Marinas <catalin.marinas@arm.com>,
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On Thu, 14 Apr 2022 at 11:54, Wupeng Ma <mawupeng1@huawei.com> wrote:
>
> From: Ma Wupeng <mawupeng1@huawei.com>
>
> Commit b05b9f5f9dcf ("x86, mirror: x86 enabling - find mirrored memory ranges")
> introduced mirrored memory support for x86. This support rely on UEFI to
> report mirrored memory address ranges.  See UEFI 2.5 spec pages 157-158:
>
>   http://www.uefi.org/sites/default/files/resources/UEFI%202_5.pdf
>
> Memory mirroring is a technique used to separate memory into two separate
> channels, usually on a memory device, like a server. In memory mirroring,
> one channel is copied to another to create redundancy. This method makes
> input/output (I/O) registers and memory appear with more than one address
> range because the same physical byte is accessible at more than one
> address. Using memory mirroring, higher memory reliability and a higher
> level of memory consolidation are possible.
>
> Arm64 can support this too. So mirrored memory support is added to support
> arm64.
>
> Efi_fake_mem is used for testing mirrored features and will not be used in
> production environment. This test features can fake memory's attribute
> values.
>
> The reason why efi_fake_mem support is put first is that memory's attribute
> is reported by BIOS which is hard to simulate. With this support, any arm64
> machines with efi support can easily test mirrored features.
>
> The main purpose of this patchset is to introduce mirrored support for
> arm64 and we have already fixed the problems we had which is shown in
> patch #5 to patch #7 and try to bring total isolation in patch #8 which
> will disable mirror feature if kernelcore is not specified.
>
> In order to test this support in arm64:
> - patch this patchset
> - add efi_fake_mem=8G@0:0x10000 in kernel parameter to simulate mirrored
>   memroy between phy addr 0-8G.
> - add kernelcore=mirror in kernel parameter
> - start you kernel
>

As I explained before:

- NAK to EFI fake_mem support on arm64
- NAK to the whole series until you come up with a proposal on how to
locate the static kernel image itself into more reliable memory, as
there is really no point to any of this otherwise.