From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail.ozlabs.org (gandalf.ozlabs.org [150.107.74.76]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id C0A863033F8; Fri, 12 Jun 2026 14:32:03 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=150.107.74.76 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1781274726; cv=none; b=Noh1fY5zdaJQh1QmCVCuZA8qcldqYIM254/lGiOyJv7THlayd1EtGTo4ygjmHwqj16EOxDH/v4MR1z1cEF9B+NyA8YpqlzLsQks0P7mQS5YNn0AsZEf6NxogKFLkSR26L4zjtGcFQU4ks9wniQ7PJdCcahlaOgnL125txzCa3uY= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1781274726; c=relaxed/simple; bh=VTV3R4NURHl1vPtjlguQqo2RQcpCgSd+hr7dEhm4lWE=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=gezKxbtfuhdt0JTiJdj+rIYDeFxhp9EKvhw3Hh+9kDkoVvN4dFlrFGx0uxOQQERyB+6Im/0rzSbPdt+FNRcEGQG0biEJinOYy84J46ipHrz5sMSZk04hRKq1yr9KHLBxXaMNGY2O/R8de48x1cKfyV8l1M5Y2E5X17nhpF/M0gU= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=ozlabs.org; spf=pass smtp.mailfrom=ozlabs.org; dkim=pass (2048-bit key) header.d=ozlabs.org header.i=@ozlabs.org header.b=EOwLg45D; arc=none smtp.client-ip=150.107.74.76 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=ozlabs.org Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=ozlabs.org Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=ozlabs.org header.i=@ozlabs.org header.b="EOwLg45D" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=ozlabs.org; s=201707; t=1781274721; bh=oYg/1sibtgFfC9/h6xF284nz/nnSd5DreUIEPAixkoI=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=EOwLg45DKjx6iDaghDYk9kK4wwjCVOjCkcg4exJJahYAnqK8izc/mcAILa15V1Lw+ WZvY5lJJPBAuzY0sfq6YxCSuit092SWgMIATHqOj8MQvDZYd9grb5T+2Y4kgT27Xqq 4WTUNvtPu/f8LO0RtR4DSWesenP11MoRP5ideV8DmBKUmPJid3QS6nttKavPg4/3jW nhJ0zA+9NVczIGTE9zDZ0/wp+ntipstalerasNPLL8tfLvg2Rx46Oad+JjtpviFiif 6JmXWN7efNklF145UDNG7QB9DrJCcpGL+9n6y1jSIMMz9cgSmLZF0Sgm4vVDj8p+QG CSy5Imknap0HA== Received: from authenticated.ozlabs.org (localhost [127.0.0.1]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange x25519 server-signature RSA-PSS (4096 bits) server-digest SHA256) (Client did not present a certificate) by mail.ozlabs.org (Postfix) with ESMTPSA id 4gcMQx0gWPz58ld; Sat, 13 Jun 2026 00:31:52 +1000 (AEST) Message-ID: <0dfadf98-a904-4e6a-b078-5caf27bc7922@ozlabs.org> Date: Fri, 12 Jun 2026 15:31:49 +0100 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v3 1/9] PCI/P2PDMA: Add CONFIG_PCI_P2PDMA_CORE Content-Language: en-GB To: "Tian, Kevin" , Pranjal Shrivastava , Robin Murphy Cc: Alex Williamson , Leon Romanovsky , Jason Gunthorpe , Alex Mastro , =?UTF-8?Q?Christian_K=C3=B6nig?= , Bjorn Helgaas , Logan Gunthorpe , Mahmoud Adam , David Matlack , =?UTF-8?B?QmrDtnJuIFTDtnBlbA==?= , Sumit Semwal , Ankit Agrawal , Alistair Popple , "Kasireddy, Vivek" , "linux-kernel@vger.kernel.org" , "linux-media@vger.kernel.org" , "dri-devel@lists.freedesktop.org" , "linaro-mm-sig@lists.linaro.org" , "kvm@vger.kernel.org" , "linux-pci@vger.kernel.org" References: <20260610154327.37758-1-matt@ozlabs.org> <20260610154327.37758-2-matt@ozlabs.org> From: Matt Evans In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Hi Kevin, Pranjal, (+Robin, hi!) On 12/06/2026 04:39, Tian, Kevin wrote: >> From: Pranjal Shrivastava >> Sent: Friday, June 12, 2026 2:38 AM >> >> On Wed, Jun 10, 2026 at 04:43:15PM +0100, Matt Evans wrote: >>> --- a/drivers/pci/Kconfig >>> +++ b/drivers/pci/Kconfig >>> @@ -206,11 +206,7 @@ config PCIE_TPH >>> config PCI_P2PDMA >>> bool "PCI peer-to-peer transfer support" >>> depends on ZONE_DEVICE >>> - # >>> - # The need for the scatterlist DMA bus address flag means PCI >> P2PDMA >>> - # requires 64bit >>> - # >>> - depends on 64BIT >>> + select PCI_P2PDMA_CORE >>> select GENERIC_ALLOCATOR >>> select NEED_SG_DMA_FLAGS >>> help >> >> Nit: Did we drop depends on 64BIT intentionally here? I guess the full >> PCI_P2PDMA stack still selects NEED_SG_DMA_FLAGS? IIRC, >> NEED_SG_DMA_FLAGS doesn't select 64BIT? > > seems that comment is stale. According to the commit msg: > > " it would make vfio-pci only available if CONFIG_ZONE_DEVICE is > present (e.g. 64-bit systems), " > > so it sounds a redundant dependency hence is removed. This was intentional. In practice there is still a dependency on 64BIT for PCI_P2PDMA, but it is because of ZONE_DEVICE (and mem hotplug). The key need is PCI_P2PDMA_CORE is available on !64BIT for VFIO, but I didn't see a requirement from PCI_P2PDMA itself (as opposed to its dependencies). If I've missed one, I can put it back... But NEED_SG_DMA_FLAGS doesn't smell quite right; I see from comments in af2880ec44021 ("scatterlist: add dedicated config for DMA flags") that it assumes 64BIT, but it seems to be missing a "depends on 64BIT". Robin -- should that depend on 64BIT? Cheers, Matt