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Date:   Wed, 22 Sep 2021 10:22:32 +0300
From:   Mike Rapoport <rppt@kernel.org>
To:     Christoph Hellwig <hch@lst.de>
Cc:     Catalin Marinas <catalin.marinas@arm.com>,
        David Hildenbrand <david@redhat.com>,
        Robin Murphy <robin.murphy@arm.com>,
        Alex Bee <knaerzche@gmail.com>, Will Deacon <will@kernel.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        Anshuman Khandual <anshuman.khandual@arm.com>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        linux-mm@kvack.org,
        Linux ARM <linux-arm-kernel@lists.infradead.org>
Subject: Re: [BUG 5.14] arm64/mm: dma memory mapping fails (in some cases)
Message-ID: <YUrZuKSaDnJ+rO0k@kernel.org>
References: <60a11eba-2910-3b5f-ef96-97d4556c1596@redhat.com>
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 <20210918051843.GA16104@lst.de>
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 <20210921082007.GA29121@lst.de>
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On Tue, Sep 21, 2021 at 05:38:05PM +0200, Christoph Hellwig wrote:
> On Tue, Sep 21, 2021 at 12:34:10PM +0300, Mike Rapoport wrote:
> > > It doesn't create any new mappings.  The only real issue is that it
> > > does the wrong thing for RAM in a way that might not be noticed on
> > > simple (x86/PC) platforms.
> > 
> > But if the mapping request was rejected by devm_ioremap_resource() because
> > of an attempt to map RAM, why we would get to dma_map_resource() at all? 
> 
> dma_map_resource takes a phys_addr_t that could come from anywhere.

Right, but it's not different from, say, dma_map_page_attrs() that can get a
struct page from anywhere and there is no actual memory for that struct
page at all. Do you suggest add a check that that struct page is backed by
memory in dma_map_page_attrs() as well?

-- 
Sincerely yours,
Mike.