From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by smtp.subspace.kernel.org (Postfix) with ESMTP id 32EA7187853 for ; Mon, 29 Jul 2024 14:27:21 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=217.140.110.172 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1722263243; cv=none; b=VTBU18gu2tIGh85TD9ccnJTEX/DpKT8CNqb/3bGNVTatJr2THST6k5QR12d2kK3P5XCoCh7OIUEfBAc1+QrN16Rj86AgkWQScI5Us7QLY3xOHzWEUaRZlMRZbUwng+T6Rab6XbW8SfKKrKQO24LvJCou1yRRVKswZLolDHo8ssY= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1722263243; c=relaxed/simple; bh=FI0SZtq1fJLkD6eYgak6HSBpiN7qQvZbSjMTOy9yP0I=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=SF4Z/c5mhXuvfaG6VeVWFpxcaA3gwmdB39J2ORPdZFRoZ8+KF+qaLWpSU4Npn/UHFILvtBwDhVGax2CokTU+k4j/b0/aXB1Z84FBmHPgydRch/0o/L9N0vcAq9d+MVsPCvuD/AZZEE25gyZ4CJbNSdRwMh6N/lkrmjAgTZyCMY8= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=arm.com; spf=pass smtp.mailfrom=arm.com; arc=none smtp.client-ip=217.140.110.172 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=arm.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=arm.com 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 38AA21007; Mon, 29 Jul 2024 07:27:46 -0700 (PDT) Received: from e133380.arm.com (e133380.arm.com [10.1.197.55]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id CD7413F64C; Mon, 29 Jul 2024 07:27:16 -0700 (PDT) Date: Mon, 29 Jul 2024 15:27:11 +0100 From: Dave Martin To: Mark Brown Cc: Amit Daniel Kachhap , Joey Gouly , linux-arm-kernel@lists.infradead.org, akpm@linux-foundation.org, aneesh.kumar@kernel.org, aneesh.kumar@linux.ibm.com, bp@alien8.de, catalin.marinas@arm.com, christophe.leroy@csgroup.eu, dave.hansen@linux.intel.com, hpa@zytor.com, linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, linuxppc-dev@lists.ozlabs.org, maz@kernel.org, mingo@redhat.com, mpe@ellerman.id.au, naveen.n.rao@linux.ibm.com, npiggin@gmail.com, oliver.upton@linux.dev, shuah@kernel.org, szabolcs.nagy@arm.com, tglx@linutronix.de, will@kernel.org, x86@kernel.org, kvmarm@lists.linux.dev Subject: Re: [PATCH v4 18/29] arm64: add POE signal support Message-ID: References: <20240503130147.1154804-1-joey.gouly@arm.com> <20240503130147.1154804-19-joey.gouly@arm.com> <229bd367-466e-4bf9-9627-24d2d0821ff4@arm.com> <7789da64-34e2-49db-b203-84b80e5831d5@sirena.org.uk> Precedence: bulk X-Mailing-List: linux-fsdevel@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: On Fri, Jul 26, 2024 at 06:39:27PM +0100, Mark Brown wrote: > On Fri, Jul 26, 2024 at 05:14:01PM +0100, Dave Martin wrote: > > On Thu, Jul 25, 2024 at 07:11:41PM +0100, Mark Brown wrote: > > > > That'd have to be a variably sized structure with pairs of sysreg > > > ID/value items in it I think which would be a bit of a pain to implement > > > but doable. The per-record header is 64 bits, we'd get maximal saving > > > by allocating a byte for the IDs. > > > Or possibly the regs could be identified positionally, avoiding the > > need for IDs. Space would be at a premium, and we would have to think > > carefully about what should and should not be allowed in there. > > Yes, though that would mean if we had to generate any register in there > we'd always have to generate at least as many entries as whatever number > it got assigned which depending on how much optionality ends up getting > used might be unfortunate. Ack, though it's only 150 bytes or so at most, so just zeroing it all (or as much as we know about) doesn't feel like a big cost. It depends how determined we are to squeeze the most out of the remaining space. > > > It would be very unfortunate timing to start gating things on such a > > > change though (I'm particularly worried about GCS here, at this point > > > the kernel changes are blocking the entire ecosystem). > > > For GCS, I wonder whether it should be made a strictly opt-in feature: > > i.e., if you use it then you must tolerate large sigframes, and if it > > is turned off then its state is neither dumped nor restored. Since GCS > > requires an explict prctl to turn it on, the mechanism seems partly > > there already in your series. > > Yeah, that's what the current code does actually. In any case it's not > just a single register - there's also the GCS mode in there. Agreed -- I'll ping the GCS series, but this sounds like a reasonable starting point. Cheers ---Dave