From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752503AbdEFLZP (ORCPT ); Sat, 6 May 2017 07:25:15 -0400 Received: from foss.arm.com ([217.140.101.70]:58512 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750907AbdEFLZK (ORCPT ); Sat, 6 May 2017 07:25:10 -0400 From: Marc Zyngier To: Shanker Donthineni Cc: Vikram Sethi , Thomas Gleixner , linux-kernel , linux-arm-kernel , Jason Cooper Subject: Re: [PATCH v4] irqchip/gicv3-its: Avoid memory over allocation for ITEs In-Reply-To: (Shanker Donthineni's message of "Fri, 5 May 2017 17:04:22 -0500") Organization: ARM Ltd References: <1493562975-14365-1-git-send-email-shankerd@codeaurora.org> <87lgqfmdy7.fsf@on-the-bus.cambridge.arm.com> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/24.5 (gnu/linux) Date: Sat, 06 May 2017 12:25:02 +0100 Message-ID: <87vapekz1t.fsf@on-the-bus.cambridge.arm.com> MIME-Version: 1.0 Content-Type: text/plain Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, May 05 2017 at 11:04:22 pm BST, Shanker Donthineni wrote: > Hi Marc, > > > On 05/02/2017 11:16 AM, Marc Zyngier wrote: >> On Sun, Apr 30 2017 at 3:36:15 pm BST, Shanker Donthineni wrote: >>> We are always allocating extra 255Bytes of memory to handle ITE >>> physical address alignment requirement. The kmalloc() satisfies >>> the ITE alignment since the ITS driver is requesting a minimum >>> size of ITS_ITT_ALIGN bytes. >>> >>> Let's try to allocate the exact amount of memory that is required >>> for ITEs to avoid wastage. >>> >>> Signed-off-by: Shanker Donthineni >>> --- >>> Changes: >>> v2: removed 'Change-Id: Ia8084189833f2081ff13c392deb5070c46a64038' from commit. >>> v3: changed from IITE to ITE. >>> v3: removed fallback since kmalloc() guarantees the right alignment. >>> >>> drivers/irqchip/irq-gic-v3-its.c | 6 +++--- >>> 1 file changed, 3 insertions(+), 3 deletions(-) >>> >>> diff --git a/drivers/irqchip/irq-gic-v3-its.c b/drivers/irqchip/irq-gic-v3-its.c >>> index 45ea1933..72e56f03 100644 >>> --- a/drivers/irqchip/irq-gic-v3-its.c >>> +++ b/drivers/irqchip/irq-gic-v3-its.c >>> @@ -261,7 +261,6 @@ static struct its_collection *its_build_mapd_cmd(struct its_cmd_block *cmd, >>> u8 size = ilog2(desc->its_mapd_cmd.dev->nr_ites); >>> >>> itt_addr = virt_to_phys(desc->its_mapd_cmd.dev->itt); >>> - itt_addr = ALIGN(itt_addr, ITS_ITT_ALIGN); >>> >>> its_encode_cmd(cmd, GITS_CMD_MAPD); >>> its_encode_devid(cmd, desc->its_mapd_cmd.dev->device_id); >>> @@ -1329,13 +1328,14 @@ static struct its_device *its_create_device(struct its_node *its, u32 dev_id, >>> */ >>> nr_ites = max(2UL, roundup_pow_of_two(nvecs)); >>> sz = nr_ites * its->ite_size; >>> - sz = max(sz, ITS_ITT_ALIGN) + ITS_ITT_ALIGN - 1; >>> + sz = max(sz, ITS_ITT_ALIGN); >>> itt = kzalloc(sz, GFP_KERNEL); >>> lpi_map = its_lpi_alloc_chunks(nvecs, &lpi_base, &nr_lpis); >>> if (lpi_map) >>> col_map = kzalloc(sizeof(*col_map) * nr_lpis, GFP_KERNEL); >>> >>> - if (!dev || !itt || !lpi_map || !col_map) { >>> + if (!dev || !itt || !lpi_map || !col_map || >>> + !IS_ALIGNED(virt_to_phys(itt), ITS_ITT_ALIGN)) { >>> kfree(dev); >>> kfree(itt); >>> kfree(lpi_map); >> I'm confused. Either the alignment is guaranteed (and you should >> document why it is so), or it is not, and we need to handle the >> non-alignment (instead of failing). > > Sorry for confusion, alignment is guaranteed by kmalloc(), added a > check for readability purpose only can be removed. My question still remains. Where exactly is that alignment guarantee documented and enforced? I can't see anything giving that certainty. I would expect kmalloc to give you something that is cache-line aligned, but probably nothing more than that. Now, I'd happily be proven wrong, but so far, all I can see is that: - ARCH_KMALLOC_MINALIGN is defined as ARCH_DMA_MINALIGN - ARCH_DMA_MINALIGN is defined as L1_CACHE_BYTES - L1_CACHE_BYTES is 128 on arm64, and either 32, 64, or 128 on arm. What am I missing? Thanks, M. -- Jazz is not dead, it just smell funny.