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Date:   Fri, 24 Nov 2023 20:51:38 +0100
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Subject: Re: [PATCH RFC v2 13/27] arm64: mte: Make tag storage depend on
 ARCH_KEEP_MEMBLOCK
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To:     Alexandru Elisei <alexandru.elisei@arm.com>,
        catalin.marinas@arm.com, will@kernel.org, oliver.upton@linux.dev,
        maz@kernel.org, james.morse@arm.com, suzuki.poulose@arm.com,
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References: <20231119165721.9849-1-alexandru.elisei@arm.com>
 <20231119165721.9849-14-alexandru.elisei@arm.com>
From:   David Hildenbrand <david@redhat.com>
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In-Reply-To: <20231119165721.9849-14-alexandru.elisei@arm.com>
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Precedence: bulk

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@arm.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