From mboxrd@z Thu Jan 1 00:00:00 1970 Authentication-Results: smtp.subspace.kernel.org; dkim=none Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by lindbergh.monkeyblade.net (Postfix) with ESMTP id 270B81BC6; Wed, 29 Nov 2023 02:46:14 -0800 (PST) Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id EEA3E2F4; Wed, 29 Nov 2023 02:47:00 -0800 (PST) Received: from raptor (unknown [172.31.20.19]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 857663F5A1; Wed, 29 Nov 2023 02:46:08 -0800 (PST) Date: Wed, 29 Nov 2023 10:46:05 +0000 From: Alexandru Elisei To: David Hildenbrand 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 Subject: Re: [PATCH RFC v2 13/27] arm64: mte: Make tag storage depend on ARCH_KEEP_MEMBLOCK Message-ID: References: <20231119165721.9849-1-alexandru.elisei@arm.com> <20231119165721.9849-14-alexandru.elisei@arm.com> <91c5d2e2-57b1-4172-88e0-cd07a8d85af4@redhat.com> Precedence: bulk X-Mailing-List: linux-trace-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Hi, On Tue, Nov 28, 2023 at 06:05:20PM +0100, David Hildenbrand wrote: > 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 can do that, sure. Thanks, Alex > > 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 >