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Date:   Sat, 16 Apr 2022 09:32:01 +0800
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Subject: Re: [PATCH v2 0/9] introduce mirrored memory support for arm64
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From:   mawupeng <mawupeng1@huawei.com>
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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?

What is the loader signal?
System exists mirrored memory reported by uefi?

Thanks for reviewing, sorry for my ignorance on this.

> .