linux-kernel - Re: [PATCH v9 10/24] mm/hmm: let users to tag specific PFN with DMA mapped bit

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20250423181706.GT1213339@ziepe.ca>
Date: Wed, 23 Apr 2025 15:17:06 -0300
From: Jason Gunthorpe <jgg@...pe.ca>
To: Mika Penttilä <mpenttil@...hat.com>
Cc: Leon Romanovsky <leon@...nel.org>,
	Marek Szyprowski <m.szyprowski@...sung.com>,
	Jens Axboe <axboe@...nel.dk>, Christoph Hellwig <hch@....de>,
	Keith Busch <kbusch@...nel.org>,
	Leon Romanovsky <leonro@...dia.com>, Jake Edge <jake@....net>,
	Jonathan Corbet <corbet@....net>, Zhu Yanjun <zyjzyj2000@...il.com>,
	Robin Murphy <robin.murphy@....com>, Joerg Roedel <joro@...tes.org>,
	Will Deacon <will@...nel.org>, Sagi Grimberg <sagi@...mberg.me>,
	Bjorn Helgaas <bhelgaas@...gle.com>,
	Logan Gunthorpe <logang@...tatee.com>,
	Yishai Hadas <yishaih@...dia.com>,
	Shameer Kolothum <shameerali.kolothum.thodi@...wei.com>,
	Kevin Tian <kevin.tian@...el.com>,
	Alex Williamson <alex.williamson@...hat.com>,
	Jérôme Glisse <jglisse@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-block@...r.kernel.org, linux-rdma@...r.kernel.org,
	iommu@...ts.linux.dev, linux-nvme@...ts.infradead.org,
	linux-pci@...r.kernel.org, kvm@...r.kernel.org, linux-mm@...ck.org,
	Niklas Schnelle <schnelle@...ux.ibm.com>,
	Chuck Lever <chuck.lever@...cle.com>,
	Luis Chamberlain <mcgrof@...nel.org>,
	Matthew Wilcox <willy@...radead.org>,
	Dan Williams <dan.j.williams@...el.com>,
	Kanchan Joshi <joshi.k@...sung.com>,
	Chaitanya Kulkarni <kch@...dia.com>
Subject: Re: [PATCH v9 10/24] mm/hmm: let users to tag specific PFN with DMA
 mapped bit

On Wed, Apr 23, 2025 at 08:54:05PM +0300, Mika Penttilä wrote:
> > @@ -36,6 +38,13 @@ enum hmm_pfn_flags {
> >  	HMM_PFN_VALID = 1UL << (BITS_PER_LONG - 1),
> >  	HMM_PFN_WRITE = 1UL << (BITS_PER_LONG - 2),
> >  	HMM_PFN_ERROR = 1UL << (BITS_PER_LONG - 3),
> > +
> > +	/*
> > +	 * Sticky flags, carried from input to output,
> > +	 * don't forget to update HMM_PFN_INOUT_FLAGS
> > +	 */
> > +	HMM_PFN_DMA_MAPPED = 1UL << (BITS_PER_LONG - 7),
> > +
> 
> How is this playing together with the mapped order usage?

Order shift starts at bit 8, DMA_MAPPED is at bit 7

The pfn array is linear and simply indexed. The order is intended for
page table like HW to be able to build larger entries from the hmm
data without having to scan for contiguity.

Even if order is present the entry is still replicated across all the
pfns that are inside the order.

At least this series should replicate the dma_mapped flag as well as
it doesn't pay attention to order.

I suspect a page table implementation may need to make some small
changes. Indeed with guarenteed contiguous IOVA there may be a
significant optimization available to have the HW page table cover all
the contiguous present pages in the iommu, which would be a higher
order than the pages themselves. However this would require being able
to punch non-present holes into contiguous mappings...

Jason