From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 9BD55E6FE27 for ; Fri, 6 Sep 2024 15:28:46 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender:List-Subscribe:List-Help :List-Post:List-Archive:List-Unsubscribe:List-Id:Content-Transfer-Encoding: Content-Type:In-Reply-To:From:References:Cc:To:Subject:MIME-Version:Date: Message-ID:Reply-To:Content-ID:Content-Description:Resent-Date:Resent-From: Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Owner; bh=wKIrx7Jb7dPkvOEyhcveCMYyNNHIBz2yzN8yAJEKZ3c=; b=AVdpsKmm/zEYKIK1FAQFb9G8Li 0B21HxlHsApb4L/CIcgUvmEdIV5KQrUqEPbrTXasJWpeVeR/OkbR2iAdUxuM9sVI4/eyqhcIWMcWV RprFdpFNsj+hm5HgJj6itTkrmgDo7HpuCS2T8XcxAGrnJjC1tRUeYdBcvM3u7oR7PTXECBFYGydId B2y1XQncvvdaGLQb2NiX/pf6OlIfmbqymTPsey0M9lfeUvFdVQwFrLVgLAh4sng96VWAEUXW+4a+8 7MgqXK/0cC/8aEf4QuIp6eYxX0mdciPDSZnV+h5tMwCQ2HmCnyuOXSvQzhIcMEQ35KJjN3byqLyVH NAp3v5zA==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.97.1 #2 (Red Hat Linux)) id 1smat1-0000000Clxd-1u1l; Fri, 06 Sep 2024 15:28:35 +0000 Received: from foss.arm.com ([217.140.110.172]) by bombadil.infradead.org with esmtp (Exim 4.97.1 #2 (Red Hat Linux)) id 1smapw-0000000Cl8x-1EFB for linux-arm-kernel@lists.infradead.org; Fri, 06 Sep 2024 15:25:27 +0000 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 EA5FEFEC; Fri, 6 Sep 2024 08:25:49 -0700 (PDT) Received: from [10.1.196.40] (e121345-lin.cambridge.arm.com [10.1.196.40]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id EFFDF3F73F; Fri, 6 Sep 2024 08:25:20 -0700 (PDT) Message-ID: <8e17f1ac-0178-454b-b9dc-bb14ad6c465b@arm.com> Date: Fri, 6 Sep 2024 16:25:19 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] Revert "iommu/io-pgtable-arm: Optimise non-coherent unmap" To: Will Deacon Cc: Rob Clark , iommu@lists.linux.dev, linux-arm-msm@vger.kernel.org, freedreno@lists.freedesktop.org, Ashish Mhetre , Rob Clark , Joerg Roedel , "moderated list:ARM SMMU DRIVERS" , open list References: <20240905124956.84932-1-robdclark@gmail.com> <20240905155330.GA15246@willie-the-truck> <53f13813-a515-475a-836d-0b6017a117eb@arm.com> <20240906105656.GA16124@willie-the-truck> From: Robin Murphy Content-Language: en-GB In-Reply-To: <20240906105656.GA16124@willie-the-truck> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20240906_082524_564585_FCC7247E X-CRM114-Status: GOOD ( 23.78 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On 06/09/2024 11:56 am, Will Deacon wrote: > On Thu, Sep 05, 2024 at 05:27:28PM +0100, Robin Murphy wrote: >> On 05/09/2024 4:53 pm, Will Deacon wrote: >>> On Thu, Sep 05, 2024 at 05:49:56AM -0700, Rob Clark wrote: >>>> From: Rob Clark >>>> >>>> This reverts commit 85b715a334583488ad7fbd3001fe6fd617b7d4c0. >>>> >>>> It was causing gpu smmu faults on x1e80100. >>>> >>>> I _think_ what is causing this is the change in ordering of >>>> __arm_lpae_clear_pte() (dma_sync_single_for_device() on the pgtable >>>> memory) and io_pgtable_tlb_flush_walk(). I'm not entirely sure how >>>> this patch is supposed to work correctly in the face of other >>>> concurrent translations (to buffers unrelated to the one being >>>> unmapped(), because after the io_pgtable_tlb_flush_walk() we can have >>>> stale data read back into the tlb. >>>> >>>> Signed-off-by: Rob Clark >>>> --- >>>> drivers/iommu/io-pgtable-arm.c | 31 ++++++++++++++----------------- >>>> 1 file changed, 14 insertions(+), 17 deletions(-) >>> >>> Please can you try the diff below, instead? >> >> Given that the GPU driver's .tlb_add_page is a no-op, I can't see this >> making a difference. In fact, given that msm_iommu_pagetable_unmap() still >> does a brute-force iommu_flush_iotlb_all() after io-pgtable returns, and in >> fact only recently made .tlb_flush_walk start doing anything either for the >> sake of the map path, I'm now really wondering how this patch has had any >> effect at all... :/ > > Hmm, yup. Looks like Rob has come back to say the problem lies elsewhere > anyway. > > One thing below though... > >>> >>> Will >>> >>> --->8 >>> >>> diff --git a/drivers/iommu/io-pgtable-arm.c b/drivers/iommu/io-pgtable-arm.c >>> index 0e67f1721a3d..0a32e9499e2c 100644 >>> --- a/drivers/iommu/io-pgtable-arm.c >>> +++ b/drivers/iommu/io-pgtable-arm.c >>> @@ -672,7 +672,7 @@ static size_t __arm_lpae_unmap(struct arm_lpae_io_pgtable *data, >>> /* Clear the remaining entries */ >>> __arm_lpae_clear_pte(ptep, &iop->cfg, i); >>> - if (gather && !iommu_iotlb_gather_queued(gather)) >>> + if (!iommu_iotlb_gather_queued(gather)) >> >> Note that this would reintroduce the latent issue which was present >> originally, wherein iommu_iotlb_gather_queued(NULL) is false, but if we >> actually allow a NULL gather to be passed to io_pgtable_tlb_add_page() it >> may end up being dereferenced (e.g. in arm-smmu-v3). > > I think there is still something to fix here. arm_lpae_init_pte() can > pass a NULL gather to __arm_lpae_unmap() and I don't think skipping the > invalidation is correct in that case. Either the drivers need to handle > that or we shouldn't be passing NULL. > > What do you think? The subtlety there is that in that case it's always a non-leaf PTE, so all that goes back to the driver is io_pgtable_tlb_flush_walk() and the gather is never used. Thanks, Robin.