linux-kernel - Re: [BUG 5.14] arm64/mm: dma memory mapping fails (in some cases)

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Date:   Wed, 25 Aug 2021 13:54:45 +0300
From:   Mike Rapoport <rppt@...nel.org>
To:     David Hildenbrand <david@...hat.com>
Cc:     Catalin Marinas <catalin.marinas@....com>,
        Robin Murphy <robin.murphy@....com>,
        Alex Bee <knaerzche@...il.com>, Will Deacon <will@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Anshuman Khandual <anshuman.khandual@....com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-mm@...ck.org,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        Christoph Hellwig <hch@....de>
Subject: Re: [BUG 5.14] arm64/mm: dma memory mapping fails (in some cases)

On Wed, Aug 25, 2021 at 12:38:31PM +0200, David Hildenbrand wrote:
> On 25.08.21 12:20, Catalin Marinas wrote:
>
> > I can see the documentation for pfn_valid() does not claim anything more
> > than the presence of an memmap entry. But I wonder whether the confusion
> > is wider-spread than just the DMA code. At a quick grep, try_ram_remap()
> > assumes __va() can be used on pfn_valid(), though I suspect it relies on
> > the calling function to check that the resource was RAM. The arm64
> > kern_addr_valid() returns true based on pfn_valid() and kcore.c uses
> > standard memcpy on it, which wouldn't work for I/O (should we change
> > this check to pfn_is_map_memory() for arm64?).
> 
> kern_addr_valid() checks that there is a direct map entry, and that the
> mapped address has a valid mmap. (copied from x86-64)
> 
> Would you expect to have a direct map for memory holes and similar (IOW,
> !System RAM)?

I don't see where will it bail out for an IOMEM mapping before doing the
pfn_valid() check...
 
-- 
Sincerely yours,
Mike.