linux-kernel - Re: [PATCH] arm64: Enable CONFIG

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Date:	Mon, 16 Mar 2015 15:19:41 +0100
From:	Arnd Bergmann <arnd@...db.de>
To:	Christopher Covington <cov@...eaurora.org>
Cc:	linux-arm-kernel@...ts.infradead.org,
	Catalin Marinas <Catalin.Marinas@....com>,
	Michael Matz <matz@...e.de>, Will Deacon <will.deacon@....com>,
	Alexander Graf <agraf@...e.de>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Dirk Müller <dmueller@...e.com>,
	Suravee Suthikulanit <suravee.suthikulpanit@....com>,
	Andreas Schwab <schwab@...e.de>
Subject: Re: [PATCH] arm64: Enable CONFIG_COMPAT also for 64k page size

On Monday 16 March 2015 10:16:37 Christopher Covington wrote:
> 
> On 03/11/2015 08:47 AM, Arnd Bergmann wrote:
> > On Wednesday 11 March 2015 06:24:16 Alexander Graf wrote:
> >> So after recompiling all of the distribution with newer binutils we now
> >> have an openSUSE Factory tree that has 64k aligned 32bit binaries.
> >>
> >> Unfortunately however, the 32bit glibc has a bogus mmap() implementation
> >> that hard codes 4k page size.
> >>
> >> With the patch below applied to glibc, I can successfully run 32bit user
> >> space on Seattle with 64k PAGE_SIZE though. So I guess we'll need to fix
> >> up glibc next.
> >>
> >> Do you know of anyone who's fluent enough in 32bit ARM assembly to
> >> convert the hard coded assumptions in there to instead use a variable
> >> that takes the actual host page size into account?
> > 
> > I believe this is a kernel bug, and the kernel API for 32-bit emulation
> > should always take the pgoff argument in 4KB units instead of PAGE_SIZE
> > units, see the implementation of sys_mmap2 in
> > arch/powerpc/kernel/sys_ppc32.c.
> > 
> > All user space programs that call mmap2 still need to make sure that
> > their arguments are PAGE_SIZE aligned, but the libc need not care
> > about this here.
> 
> What is the correct behavior for /proc/pid/pagemap, /proc/kpagecount, and
> /proc/kpageflags for a AArch32 process running on an AArch64 kernel with
> non-4K translation granule? Actual page frame number or units-of-4K frame number?
> 

Not sure, see what PowerPC does in that case.

	Arnd
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