Re: [PATCH v3 0/6] introduce mirrored memory support for arm64

[Ard Biesheuvel]

On Tue, 7 Jun 2022 at 11:16, 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.
>
> These EFI memory regions have various attributes, and the "mirrored"
> attribute is one of them. The physical memory region whose descriptors
> in EFI memory map has EFI_MEMORY_MORE_RELIABLE attribute (bit: 16) are
> mirrored. The address range mirroring feature of the kernel arranges such
> mirrored regions into normal zones and other regions into movable zones.
>
> Arm64 can support this too. So mirrored memory support is added to support
> arm64.
>
> The main purpose of this patch set is to introduce mirrored support for
> arm64 and we have already fixed the problems we had which is shown in
> patch #5 to patch #8 and try to bring total isolation in patch #9 which
> will disable mirror feature if kernelcore is not specified.
>
> In order to test this support in arm64:
> - patch this patch set
> - add kernelcore=mirror in kernel parameter
> - start you kernel
>
> Patch #1-#2 introduce mirrored memory support form arm64.
> Patch #3-#5 fix some bugs for arm64 if memory reliable is enabled.
> Patch #6 disable mirror feature if kernelcore is not specified.
>
> Thanks to Ard Biesheuvel's hard work [1], now kernel will perfer mirrored
> memory if kaslr is enabled.
>
> [1] https://lore.kernel.org/linux-arm-kernel/CAMj1kXEPVEzMgOM4+Yj6PxHA-jFuDOAUdDJSiSxy_XaP4P7LSw@xxxxxxxxxxxxxx/T/
>
> Changelog since v2:
> - remove efi_fake_mem support
> - remove Commit ("remove some redundant code in ia64 efi_init") since
>   efi_print_memmap() is not public
> - add mirror flag back on initrd memory
>
> Changelog since v1:
> - update changelog in cover letter
> - use PHYS_PFN in patch #7
>
> Ma Wupeng (6):
>   efi: Make efi_find_mirror() public
>   arm64/mirror: arm64 enabling - find mirrored memory ranges
>   mm: Ratelimited mirrored memory related warning messages
>   mm: Demote warning message in vmemmap_verify() to debug level
>   mm: Add mirror flag back on initrd memory
>   efi: Disable mirror feature if kernelcore is not specified
>

I have tested these changes on QEMU/arm64 with the patch below, and
things seem to work as expected. We have some minor issues to work out
but the general shape of this code is good.

As for the mm/ changes: does anyone mind if I take those through the
EFI tree as well? I don't think the EFI and -mm changes depend on each
other, so they can go into -mm separately as well.