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

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Date:   Thu, 14 Apr 2022 12:22:31 +0200
From:   Ard Biesheuvel <ardb@...nel.org>
To:     Wupeng Ma <mawupeng1@...wei.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>,
        Jonathan Corbet <corbet@....net>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        X86 ML <x86@...nel.org>, hpa@...cr.com,
        Darren Hart <dvhart@...radead.org>,
        Andy Shevchenko <andy@...radead.org>,
        Mike Rapoport <rppt@...nel.org>,
        "Paul E. McKenney" <paulmck@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Joerg Roedel <jroedel@...e.de>, songmuchun@...edance.com,
        macro@...am.me.uk, Frederic Weisbecker <frederic@...nel.org>,
        W_Armin@....de, John Garry <john.garry@...wei.com>,
        Sean Christopherson <seanjc@...gle.com>,
        Thomas Bogendoerfer <tsbogend@...ha.franken.de>,
        Anshuman Khandual <anshuman.khandual@....com>,
        chenhuacai@...nel.org, David Hildenbrand <david@...hat.com>,
        gpiccoli@...lia.com, Mark Rutland <mark.rutland@....com>,
        Kefeng Wang <wangkefeng.wang@...wei.com>,
        Linux Doc Mailing List <linux-doc@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        linux-efi <linux-efi@...r.kernel.org>,
        linux-ia64@...r.kernel.org, platform-driver-x86@...r.kernel.org,
        Linux Memory Management List <linux-mm@...ck.org>
Subject: Re: [PATCH v2 0/9] introduce mirrored memory support for arm64

On Thu, 14 Apr 2022 at 11:54, Wupeng Ma <mawupeng1@...wei.com> wrote:
>
> From: Ma Wupeng <mawupeng1@...wei.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
- 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.