Re: [PATCH v2 0/9] introduce mirrored memory support for arm64

[mawupeng]

在 2022/4/14 18:22, Ard Biesheuvel 写道:
> On Thu, 14 Apr 2022 at 11:54, Wupeng Ma <mawupeng1@xxxxxxxxxx> wrote:
> > From: Ma Wupeng <mawupeng1@xxxxxxxxxx>
> >
> > 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.

> .