linux-kernel - Re: [PATCH RFC v2 13/27] arm64: mte: Make tag storage depend on ARCH_KEEP

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Message-ID: <91c5d2e2-57b1-4172-88e0-cd07a8d85af4@redhat.com>
Date:   Fri, 24 Nov 2023 20:51:38 +0100
From:   David Hildenbrand <david@...hat.com>
To:     Alexandru Elisei <alexandru.elisei@....com>,
        catalin.marinas@....com, will@...nel.org, oliver.upton@...ux.dev,
        maz@...nel.org, james.morse@....com, suzuki.poulose@....com,
        yuzenghui@...wei.com, arnd@...db.de, akpm@...ux-foundation.org,
        mingo@...hat.com, peterz@...radead.org, juri.lelli@...hat.com,
        vincent.guittot@...aro.org, dietmar.eggemann@....com,
        rostedt@...dmis.org, bsegall@...gle.com, mgorman@...e.de,
        bristot@...hat.com, vschneid@...hat.com, mhiramat@...nel.org,
        rppt@...nel.org, hughd@...gle.com
Cc:     pcc@...gle.com, steven.price@....com, anshuman.khandual@....com,
        vincenzo.frascino@....com, eugenis@...gle.com, kcc@...gle.com,
        hyesoo.yu@...sung.com, linux-arm-kernel@...ts.infradead.org,
        linux-kernel@...r.kernel.org, kvmarm@...ts.linux.dev,
        linux-fsdevel@...r.kernel.org, linux-arch@...r.kernel.org,
        linux-mm@...ck.org, linux-trace-kernel@...r.kernel.org
Subject: Re: [PATCH RFC v2 13/27] arm64: mte: Make tag storage depend on
 ARCH_KEEP_MEMBLOCK

On 19.11.23 17:57, Alexandru Elisei wrote:
> Tag storage memory requires that the tag storage pages used for data are
> always migratable when they need to be repurposed to store tags.
> 
> If ARCH_KEEP_MEMBLOCK is enabled, kexec will scan all non-reserved
> memblocks to find a suitable location for copying the kernel image. The
> kernel image, once loaded, cannot be moved to another location in physical
> memory. The initialization code for the tag storage reserves the memblocks
> for the tag storage pages, which means kexec will not use them, and the tag
> storage pages can be migrated at any time, which is the desired behaviour.
> 
> However, if ARCH_KEEP_MEMBLOCK is not selected, kexec will not skip a
> region unless the memory resource has the IORESOURCE_SYSRAM_DRIVER_MANAGED
> flag, which isn't currently set by the tag storage initialization code.
> 
> Make ARM64_MTE_TAG_STORAGE depend on ARCH_KEEP_MEMBLOCK to make it explicit
> that that the Kconfig option required for it to work correctly.
> 
> Signed-off-by: Alexandru Elisei <alexandru.elisei@....com>
> ---
>   arch/arm64/Kconfig | 1 +
>   1 file changed, 1 insertion(+)
> 
> diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
> index 047487046e8f..efa5b7958169 100644
> --- a/arch/arm64/Kconfig
> +++ b/arch/arm64/Kconfig
> @@ -2065,6 +2065,7 @@ config ARM64_MTE
>   if ARM64_MTE
>   config ARM64_MTE_TAG_STORAGE
>   	bool "Dynamic MTE tag storage management"
> +	depends on ARCH_KEEP_MEMBLOCK
>   	select CONFIG_CMA
>   	help
>   	  Adds support for dynamic management of the memory used by the hardware

Doesn't arm64 select that unconditionally? Why is this required then?

-- 
Cheers,

David / dhildenb