[RFC PATCH v3 1/1] arch: arm64: Implement unaligned atomic emulation

[Will Deacon]

On Wed, Sep 30, 2026 at 07:29:22AM -0300, André Almeida wrote:
> Em 30/09/2026 04:48, Will Deacon escreveu:
> > On Tue, Sep 29, 2026 at 11:01:38PM -0300, André Almeida wrote:
> > > Implement support for emulating unaligned atomic operations on arm64.
> > > User applications that wish to enable support for this should use the
> > > pctrl() flag `PR_ARM64_UNALIGN_ATOMIC_EMULATE`.
> > > 
> > > Signed-off-by: André Almeida <andrealmeid at igalia.com>
> > > ---
> > >   arch/arm64/Kconfig                   |   6 +
> > >   arch/arm64/include/asm/exception.h   |   1 +
> > >   arch/arm64/include/asm/processor.h   |   5 +
> > >   arch/arm64/include/asm/rwonce.h      |  14 +-
> > >   arch/arm64/include/asm/thread_info.h |   1 +
> > >   arch/arm64/kernel/Makefile           |   3 +-
> > >   arch/arm64/kernel/process.c          |  15 +
> > >   arch/arm64/kernel/unaligned_atomic.c | 521 +++++++++++++++++++++++++++
> > >   arch/arm64/mm/fault.c                |  10 +
> > >   include/uapi/linux/prctl.h           |   5 +
> > >   kernel/sys.c                         |   7 +-
> > >   11 files changed, 579 insertions(+), 9 deletions(-)
> > >   create mode 100644 arch/arm64/kernel/unaligned_atomic.c
> > 
> > No.
> > 
> > I already explained to you why this doesn't work:
> > 
> > https://lore.kernel.org/r/aV1YnOetDHhKe4hz@willie-the-truck
> 
> Indeed, last time you raised some points, and then Ryan replied them. Is
> there any specific point that doesn't work? I couldn't find a reply for
> Ryan's answers:
> 
> https://lore.kernel.org/all/CABnRqDf5EQUoXu=pJ6mj4-JfwAzEfcAE2cYrNzJANFycx7cMUA@mail.gmail.com/

So rather than get involved in the discussion, you did nothing for almost
a year and then resent the exact same patch? Why?

I don't think the implementation is correct and I don't think we should
be emulating this either. I hope I made that clear last year. Ryan
thinks it's "fine" due to the locking, but I don't see how that helps
with the example I gave.

You are apparently the author of this code, so you need to get involved
in the discussion if you want to move the needle.

Will