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 9415A1D0DCB; Fri, 6 Sep 2024 15:25:23 +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=1725636326; cv=none; b=DhX/bAgf/QaamTk0WWgKT/xuJXvA+Y24NkOv5XMRlCtHA4+hr7TZd8+ym0U9eZsdmdCby9XKT0IAvjvUIYjphhc16kva5qB8ae8Uabtel6NMm5isOwUBN1UqYdFBFR2DYa+WWD1NkXzLvkPMgoVs48brvfmFv6Uk9tBG5TY0Nek= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1725636326; c=relaxed/simple; bh=NljnRnbutnsxF1J9z4hLJYKWZghTvG8RmywBz2ykkPM=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=N/u7LWWCGc3xZsiX1UAoq8SWH97j4Bil5N+iz+eNoM4Akbm5uXPiWqB3jFXiIB5HPcDgNZ6iFfsn3V0EgoY+PfPkmH+upJf/0P1PoiSz7R6gPNoOrvypXIEZ3v7uNV/vKSfy0vqCiUmONnvNR3/GpmYfzDVIKhUTCfkhdcnVIg0= 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 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 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] 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 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.