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

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Message-ID: <20250814141437.GH802098@nvidia.com>
Date: Thu, 14 Aug 2025 11:14:37 -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 Thu, Aug 14, 2025 at 04:31:06PM +0300, Leon Romanovsky wrote:
> On Thu, Aug 14, 2025 at 09:44:48AM -0300, Jason Gunthorpe wrote:
> > On Thu, Aug 14, 2025 at 03:35:06PM +0300, Leon Romanovsky wrote:
> > > > Then check attrs here, not pfn_valid.
> > > 
> > > attrs are not available in kmsan_handle_dma(). I can add it if you prefer.
> > 
> > That makes more sense to the overall design. The comments I gave
> > before were driving at a promise to never try to touch a struct page
> > for ATTR_MMIO and think this should be comphrensive to never touching
> > a struct page even if pfnvalid.
> > 
> > > > > 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.
> > > 
> > > Sure, thanks
> > 
> > I am wondering if there is some reason it was written like this in the
> > first place. Maybe we can't even do kmap here.. So perhaps if there is
> > not a strong reason to change it just continue to check pagehighmem
> > and fail.
> > 
> > if (!(attrs & ATTR_MMIO) && PageHighMem(phys_to_page(phys)))
> >    return;
> 
> Does this version good enough? There is no need to call to
> kmap_local_pfn() if we prevent PageHighMem pages.

Why make the rest of the changes though, isn't it just:

        if (PageHighMem(page))
                return;

Becomes:

        if (attrs & ATTR_MMIO))
                return;

	page = phys_to_page(phys);
	if (PageHighMem(page))
                 return;

Leave the rest as is?

Jason