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[2003:cb:c708:1d00:99ec:9656:7475:678d]) by smtp.gmail.com with ESMTPSA id d21-20020adf9b95000000b003316ad360c1sm15738401wrc.24.2023.11.28.09.05.20 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 28 Nov 2023 09:05:22 -0800 (PST) Message-ID: Date: Tue, 28 Nov 2023 18:05:20 +0100 Precedence: bulk X-Mailing-List: linux-fsdevel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH RFC v2 13/27] arm64: mte: Make tag storage depend on ARCH_KEEP_MEMBLOCK Content-Language: en-US To: Alexandru Elisei Cc: catalin.marinas@arm.com, will@kernel.org, oliver.upton@linux.dev, maz@kernel.org, james.morse@arm.com, suzuki.poulose@arm.com, yuzenghui@huawei.com, arnd@arndb.de, akpm@linux-foundation.org, mingo@redhat.com, peterz@infradead.org, juri.lelli@redhat.com, vincent.guittot@linaro.org, dietmar.eggemann@arm.com, rostedt@goodmis.org, bsegall@google.com, mgorman@suse.de, bristot@redhat.com, vschneid@redhat.com, mhiramat@kernel.org, rppt@kernel.org, hughd@google.com, pcc@google.com, steven.price@arm.com, anshuman.khandual@arm.com, vincenzo.frascino@arm.com, eugenis@google.com, kcc@google.com, hyesoo.yu@samsung.com, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, kvmarm@lists.linux.dev, linux-fsdevel@vger.kernel.org, linux-arch@vger.kernel.org, linux-mm@kvack.org, linux-trace-kernel@vger.kernel.org References: <20231119165721.9849-1-alexandru.elisei@arm.com> <20231119165721.9849-14-alexandru.elisei@arm.com> <91c5d2e2-57b1-4172-88e0-cd07a8d85af4@redhat.com> From: David Hildenbrand Autocrypt: addr=david@redhat.com; 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charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit 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 >>> --- >>> 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