Messages in this thread | | | Date | Tue, 28 Nov 2023 18:05:20 +0100 | Subject | Re: [PATCH RFC v2 13/27] arm64: mte: Make tag storage depend on ARCH_KEEP_MEMBLOCK | From | David Hildenbrand <> |
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On 27.11.23 16:04, Alexandru Elisei wrote: > Hi, > > On Fri, Nov 24, 2023 at 08:51:38PM +0100, David Hildenbrand wrote: >> 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? > > I've added this patch to make the dependancy explicit. If, in the future, arm64 > stops selecting ARCH_KEEP_MEMBLOCK, I thinkg it would be very easy to miss the > fact that tag storage depends on it. So this patch is not required per-se, it's > there to document the dependancy.
I see. Could you add some static_assert / BUILD_BUG_ON instead?
I suspect there are plenty other (undocumented) reasons why ARCH_KEEP_MEMBLOCK has to be enabled for now, and none sets ARCH_KEEP_MEMBLOCK, I suspect/
-- Cheers,
David / dhildenb
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