linux-kernel - Re: [PATCH v1 08/16] kmsan: convert kmsan_handle

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Message-ID: <20250814121316.GC699432@nvidia.com>
Date: Thu, 14 Aug 2025 09:13:16 -0300
From: Jason Gunthorpe <jgg@...dia.com>
To: Leon Romanovsky <leon@...nel.org>
Cc: Marek Szyprowski <m.szyprowski@...sung.com>,
	Abdiel Janulgue <abdiel.janulgue@...il.com>,
	Alexander Potapenko <glider@...gle.com>,
	Alex Gaynor <alex.gaynor@...il.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Christoph Hellwig <hch@....de>, Danilo Krummrich <dakr@...nel.org>,
	iommu@...ts.linux.dev, Jason Wang <jasowang@...hat.com>,
	Jens Axboe <axboe@...nel.dk>, Joerg Roedel <joro@...tes.org>,
	Jonathan Corbet <corbet@....net>, Juergen Gross <jgross@...e.com>,
	kasan-dev@...glegroups.com, Keith Busch <kbusch@...nel.org>,
	linux-block@...r.kernel.org, linux-doc@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	linux-nvme@...ts.infradead.org, linuxppc-dev@...ts.ozlabs.org,
	linux-trace-kernel@...r.kernel.org,
	Madhavan Srinivasan <maddy@...ux.ibm.com>,
	Masami Hiramatsu <mhiramat@...nel.org>,
	Michael Ellerman <mpe@...erman.id.au>,
	"Michael S. Tsirkin" <mst@...hat.com>,
	Miguel Ojeda <ojeda@...nel.org>,
	Robin Murphy <robin.murphy@....com>, rust-for-linux@...r.kernel.org,
	Sagi Grimberg <sagi@...mberg.me>,
	Stefano Stabellini <sstabellini@...nel.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	virtualization@...ts.linux.dev, Will Deacon <will@...nel.org>,
	xen-devel@...ts.xenproject.org
Subject: Re: [PATCH v1 08/16] kmsan: convert kmsan_handle_dma to use physical
 addresses

On Wed, Aug 13, 2025 at 06:07:18PM +0300, Leon Romanovsky wrote:
> > >  /* Helper function to handle DMA data transfers. */
> > > -void kmsan_handle_dma(struct page *page, size_t offset, size_t size,
> > > +void kmsan_handle_dma(phys_addr_t phys, size_t size,
> > >  		      enum dma_data_direction dir)
> > >  {
> > >  	u64 page_offset, to_go, addr;
> > > +	struct page *page;
> > > +	void *kaddr;
> > >  
> > > -	if (PageHighMem(page))
> > > +	if (!pfn_valid(PHYS_PFN(phys)))
> > >  		return;
> > 
> > Not needed, the caller must pass in a phys that is kmap
> > compatible. Maybe just leave a comment. FWIW today this is also not
> > checking for P2P or DEVICE non-kmap struct pages either, so it should
> > be fine without checks.
> 
> It is not true as we will call to kmsan_handle_dma() unconditionally in
> dma_map_phys(). The reason to it is that kmsan_handle_dma() is guarded
> with debug kconfig options and cost of pfn_valid() can be accommodated
> in that case. It gives more clean DMA code.

Then check attrs here, not pfn_valid.

> So let's keep this patch as is.

Still need to fix the remarks you clipped, do not check PageHighMem
just call kmap_local_pfn(). All thie PageHighMem stuff is new to this
patch and should not be here, it is the wrong way to use highmem.

Jason