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Message-ID: <CAMj1kXFTnqZHWZX5yhkG4+pd04JzGriFW6gjBrAnQ-LQQmEi3Q@mail.gmail.com>
Date: Thu, 2 Apr 2020 13:24:09 +0200
From: Ard Biesheuvel <ardb@...nel.org>
To: Catalin Marinas <catalin.marinas@....com>
Cc: Linux ARM <linux-arm-kernel@...ts.infradead.org>,
kernel-hardening@...ts.openwall.com, Will Deacon <will@...nel.org>,
Mark Rutland <mark.rutland@....com>
Subject: Re: [RFC PATCH] arm64: remove CONFIG_DEBUG_ALIGN_RODATA feature
On Thu, 2 Apr 2020 at 13:15, Catalin Marinas <catalin.marinas@....com> wrote:
>
> On Sun, Mar 29, 2020 at 04:12:58PM +0200, Ard Biesheuvel wrote:
> > When CONFIG_DEBUG_ALIGN_RODATA is enabled, kernel segments mapped with
> > different permissions (r-x for .text, r-- for .rodata, rw- for .data,
> > etc) are rounded up to 2 MiB so they can be mapped more efficiently.
> > In particular, it permits the segments to be mapped using level 2
> > block entries when using 4k pages, which is expected to result in less
> > TLB pressure.
> >
> > However, the mappings for the bulk of the kernel will use level 2
> > entries anyway, and the misaligned fringes are organized such that they
> > can take advantage of the contiguous bit, and use far fewer level 3
> > entries than would be needed otherwise.
> >
> > This makes the value of this feature dubious at best, and since it is not
> > enabled in defconfig or in the distro configs, it does not appear to be
> > in wide use either. So let's just remove it.
> >
> > Signed-off-by: Ard Biesheuvel <ardb@...nel.org>
>
> Happy to take this patch via the arm64 tree for 5.7 (no new
> functionality), unless you want it to go with your other relocation
> login in the EFI stub patches.
>
If you don't mind taking it for v5.7, please go ahead.
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