Re: [GIT PULL] arm64 fix for 5.14
From: Catalin Marinas <catalin.marinas@arm.com>
Date: 2021-08-31 16:56:57
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On Fri, Aug 27, 2021 at 10:16:27AM -0700, Linus Torvalds wrote:
On Fri, Aug 27, 2021 at 10:10 AM Christoph Hellwig [off-list ref] wrote:quoted
They CCed me on their earlier discussion, but I did not catch up on it until you responded to the pull request If I understood it correct it was about a platform device mapping a MMIO region (like a PCI bar), but something about section alignment cause pfn_valid to mistrigger.Yeah, so I can easily see the maxpfn numbers can easily end up being rounded up to a whole memory section etc. I think my suggested solution should JustWork(tm) - exactly because if the area is then in that "this pfn is valid" area, it will double-check the actual underlying page. That said, I think x86 avoids the problem another way - by just making sure max_pfn is exact. That works too, as long as there are no holes in the RAM map that might be used for PCI BAR's. So I think arm could fix it that way too, depending on their memory layout.
The suggested solution in the original thread was to change the generic DMA code to use memblock_is_memory() instead of pfn_valid(): https://lore.kernel.org/lkml/b720e7c8-ca44-0a25-480b-05bf49d03c35@redhat.com/ (local) Given how late we discovered this in the -rc cycle, the decision was to revert the pfn_valid() patch. We'll re-instate it at some point but someone needs to sanity check the other pfn_valid() call sites and the expected semantics. -- Catalin _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel