From: "Russell King (Oracle)" <linux@armlinux.org.uk>
To: Ard Biesheuvel <ardb@kernel.org>
Cc: Linus Walleij <linus.walleij@linaro.org>,
Arnd Bergmann <arnd@arndb.de>,
Linux ARM <linux-arm-kernel@lists.infradead.org>,
Thomas Gleixner <tglx@linutronix.de>,
Quanyang Wang <quanyang.wang@windriver.com>
Subject: Re: [PATCH] kmap_local: don't assume kmap PTEs are linear arrays in memory
Date: Fri, 5 Nov 2021 14:49:58 +0000 [thread overview]
Message-ID: <YYVElmQOUveS5voK@shell.armlinux.org.uk> (raw)
In-Reply-To: <CAMj1kXFNvXnwbCa5UnvHsdaynuKaZ7YYNg7vdoD6FMKARS=i8A@mail.gmail.com>
On Fri, Nov 05, 2021 at 03:21:00PM +0100, Ard Biesheuvel wrote:
> On Tue, 26 Oct 2021 at 15:13, Ard Biesheuvel <ardb@kernel.org> wrote:
> >
> > The kmap_local conversion broke the ARM architecture, because the new
> > code assumes that all PTEs used for creating kmaps form a linear array
> > in memory, and uses array indexing to look up the kmap PTE belonging to
> > a certain kmap index.
> >
> > On ARM, this cannot work, not only because the PTE pages may be
> > non-adjacent in memory, but also because ARM/!LPAE interleaves hardware
> > entries and extended entries (carrying software-only bits) in a way that
> > is not compatible with array indexing.
> >
> > Fortunately, this only seems to affect configurations with more than 8
> > CPUs, due to the way the per-CPU kmap slots are organized in memory.
> >
> > Work around this by permitting an architecture to set a Kconfig symbol
> > that signifies that the kmap PTEs do not form a lineary array in memory,
> > and so the only way to locate the appropriate one is to walk the page
> > tables.
> >
> > Reported-by: Quanyang Wang <quanyang.wang@windriver.com>
> > Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
> > ---
>
> Ping? Can we get this fixed please?
Who are you expecting to apply it? It seems to be touching only core
code, so I don't think it's up to me - not without some kind of review
from mm guys.
--
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next prev parent reply other threads:[~2021-11-05 14:51 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-10-26 13:12 [PATCH] kmap_local: don't assume kmap PTEs are linear arrays in memory Ard Biesheuvel
2021-11-05 14:21 ` Ard Biesheuvel
2021-11-05 14:49 ` Russell King (Oracle) [this message]
2021-11-05 15:01 ` Ard Biesheuvel
2021-11-09 11:47 ` Russell King (Oracle)
2021-11-15 7:54 ` Ard Biesheuvel
2021-11-16 4:09 ` Andrew Morton
2021-11-09 11:39 ` Linus Walleij
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