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Date:   Wed, 20 Apr 2022 10:13:40 +0800
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Subject: Re: [PATCH v2 0/9] introduce mirrored memory support for arm64
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References: <20220414101314.1250667-1-mawupeng1@huawei.com>
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From:   mawupeng <mawupeng1@huawei.com>
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在 2022/4/20 2:32, Ard Biesheuvel 写道:
> On Sat, 16 Apr 2022 at 03:32, mawupeng <mawupeng1@huawei.com> wrote:
>>
>>
>>
>> 在 2022/4/14 18:22, Ard Biesheuvel 写道:
>>> 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
>>
>> fake_mem support on arm64 will be removed in subsequent version.
>>
>>> - 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.
>>
>> Sorry I am not familiar with this, as you metioned before,
>>
>>   > you have to iterate over the memory map and look for regions with
>>   > the desired attribute, and allocate those pages explicitly.
>>
>> Do you mean this is x86, commit c05cd79750fb
>> ("x86/boot/KASLR: Prefer mirrored memory regions for the kernel physical address").
>> I will do some research.
>>
>>   > I'd prefer to implement this in the bootloader, and only add minimal
>>   > logic to the stub to respect the placement of the kernel by the loader
>>   > if the loader signals it to do so.
>>
>> Does this bootloader refer to grub and then add minimal logic to arm64-stub.c?
>>
> 
> Any bootloader, yes.
> 
>> What is the loader signal?
> 
> A protocol installed onto the image handle, as I suggested before. I
> even cc'ed you on a patch that implements this.

Sorry to bother you.
I didn't receive any patches.
Could you share the link?

> 
>> System exists mirrored memory reported by uefi?
>>
> 
> What on earth is the point of any of this if the only use case being
> targeted is efi_fake_mem with arbitrary fake mirrored regions?
> 
> So yes, unless there are systems that need this, I don't see a point
> in merging any of this
We do have mirrored memory reported by uefi and efi_fake_mem is added for easy testing
with qemu/hardware without update UEFI.

> .