LKML Archive on
help / color / mirror / Atom feed
From: Catalin Marinas <>
To: Linus Torvalds <>
Cc: Christoph Hellwig <>, Will Deacon <>,
	Linux ARM <>,
	Linux Kernel Mailing List <>,
	Android Kernel Team <>
Subject: Re: [GIT PULL] arm64 fix for 5.14
Date: Tue, 31 Aug 2021 17:56:50 +0100	[thread overview]
Message-ID: <> (raw)
In-Reply-To: <>

On Fri, Aug 27, 2021 at 10:16:27AM -0700, Linus Torvalds wrote:
> On Fri, Aug 27, 2021 at 10:10 AM Christoph Hellwig <> 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.

The suggested solution in the original thread was to change the generic
DMA code to use memblock_is_memory() instead of pfn_valid():

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.


  parent reply	other threads:[~2021-08-31 16:56 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
2021-08-31 13:31           ` Will Deacon
2021-08-31 19:16             ` David Hildenbrand
2021-08-31 16:56           ` Catalin Marinas [this message]
2021-08-26 18:52 ` pr-tracker-bot

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \ \ \ \ \ \ \ \ \
    --subject='Re: [GIT PULL] arm64 fix for 5.14' \

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).