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Date:   Sat, 11 Jun 2022 12:56:12 +0300
From:   Mike Rapoport <rppt@kernel.org>
To:     Ard Biesheuvel <ardb@kernel.org>
Cc:     Wupeng Ma <mawupeng1@huawei.com>,
        Andrew Morton <akpm@linux-foundation.org>,
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Subject: Re: [PATCH v3 0/6] introduce mirrored memory support for arm64
Message-ID: <YqRmvJDiy2UQkEDu@kernel.org>
References: <20220607093805.1354256-1-mawupeng1@huawei.com>
 <CAMj1kXH5r=CUoLCndBUsZ04_0UCJ2VqgJDdp2wbdNCtEx0Yxag@mail.gmail.com>
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On Fri, Jun 10, 2022 at 01:23:34PM +0200, Ard Biesheuvel wrote:
> On Tue, 7 Jun 2022 at 11:16, 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.
> >
> > 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@mail.gmail.com/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?

No objections from me.

> I don't think the EFI and -mm changes depend on each other, so they
> can go into -mm separately as well.

--
Sincerely yours,
Mike.