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Date: Thu, 12 Dec 2024 09:48:56 +0100
From: Christoph Hellwig <hch@lst.de>
To: Leon Romanovsky <leon@kernel.org>
Cc: Jens Axboe <axboe@kernel.dk>, Jason Gunthorpe <jgg@ziepe.ca>,
	Robin Murphy <robin.murphy@arm.com>, Joerg Roedel <joro@8bytes.org>,
	Will Deacon <will@kernel.org>, Christoph Hellwig <hch@lst.de>,
	Sagi Grimberg <sagi@grimberg.me>,
	Leon Romanovsky <leonro@nvidia.com>,
	Keith Busch <kbusch@kernel.org>,
	Bjorn Helgaas <bhelgaas@google.com>,
	Logan Gunthorpe <logang@deltatee.com>,
	Yishai Hadas <yishaih@nvidia.com>,
	Shameer Kolothum <shameerali.kolothum.thodi@huawei.com>,
	Kevin Tian <kevin.tian@intel.com>,
	Alex Williamson <alex.williamson@redhat.com>,
	Marek Szyprowski <m.szyprowski@samsung.com>,
	=?iso-8859-1?B?Suly9G1l?= Glisse <jglisse@redhat.com>,
	Andrew Morton <akpm@linux-foundation.org>,
	Jonathan Corbet <corbet@lwn.net>, linux-doc@vger.kernel.org,
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	Randy Dunlap <rdunlap@infradead.org>
Subject: Re: [PATCH v4 11/18] mm/hmm: let users to tag specific PFN with
 DMA mapped bit
Message-ID: <20241212084856.GE9376@lst.de>
References: <cover.1733398913.git.leon@kernel.org> <e4551571fc10d9c73ab9e38a75ea701c1b492686.1733398913.git.leon@kernel.org>
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In-Reply-To: <e4551571fc10d9c73ab9e38a75ea701c1b492686.1733398913.git.leon@kernel.org>
User-Agent: Mutt/1.5.17 (2007-11-01)

On Thu, Dec 05, 2024 at 03:21:10PM +0200, Leon Romanovsky wrote:
> From: Leon Romanovsky <leonro@nvidia.com>
> 
> Introduce new sticky flag (HMM_PFN_DMA_MAPPED), which isn't overwritten
> by HMM range fault. Such flag allows users to tag specific PFNs with information
> if this specific PFN was already DMA mapped.

Missing line wrap at 73 characters here.

>  
> @@ -253,14 +262,14 @@ static int hmm_vma_handle_pte(struct mm_walk *walk, unsigned long addr,
>  			cpu_flags = HMM_PFN_VALID;
>  			if (is_writable_device_private_entry(entry))
>  				cpu_flags |= HMM_PFN_WRITE;
> -			*hmm_pfn = swp_offset_pfn(entry) | cpu_flags;
> +			*hmm_pfn = (*hmm_pfn & HMM_PFN_INOUT_FLAGS) | swp_offset_pfn(entry) | cpu_flags;

Please avoid the overly long line here.

That being said I hate the structure here.  Can't we just have a local
variable for the actual new pfn value, and then a single goto label
at the end that takes the keeper flags from the argument and assigning
the new out value to *hmm_pfn instead of duplicating this in half a
dozen places?