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From: Linus Torvalds <torvalds@linux-foundation.org>
To: Christoph Hellwig <hch@lst.de>
Cc: Will Deacon <will@kernel.org>,
	Catalin Marinas <catalin.marinas@arm.com>,
	Linux ARM <linux-arm-kernel@lists.infradead.org>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	Android Kernel Team <kernel-team@android.com>
Subject: Re: [GIT PULL] arm64 fix for 5.14
Date: Fri, 27 Aug 2021 10:16:27 -0700	[thread overview]
Message-ID: <CAHk-=wg=+P1+HQXhrszxN_BgWtLc-=dWiT61KzogcJU3hnLrtQ@mail.gmail.com> (raw)
In-Reply-To: <20210827171041.GA28149@lst.de>

On Fri, Aug 27, 2021 at 10:10 AM Christoph Hellwig <hch@lst.de> wrote:
>
> 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.

(x86 has that traditional hole at A0000-FFFFF, but it's special enough
that it presumably is never an issue).

                  Linus

  reply	other threads:[~2021-08-27 17:16 UTC|newest]

Thread overview: 10+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-08-26 13:17 Will Deacon
2021-08-26 18:41 ` Linus Torvalds
2021-08-27  7:40   ` Christoph Hellwig
2021-08-27 17:03     ` Linus Torvalds
2021-08-27 17:10       ` Christoph Hellwig
2021-08-27 17:16         ` Linus Torvalds [this message]
2021-08-31 13:31           ` Will Deacon
2021-08-31 19:16             ` David Hildenbrand
2021-08-31 16:56           ` Catalin Marinas
2021-08-26 18:52 ` pr-tracker-bot

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