Re: [v5 PATCH] arm64: mm: force write fault for atomic RMW instructions

[Christoph Lameter (Ampere)]

On Fri, 28 Jun 2024, Catalin Marinas wrote:

> On Wed, Jun 26, 2024 at 12:18:30PM -0700, Yang Shi wrote:
> > @@ -568,6 +596,12 @@ static int __kprobes do_page_fault(unsigned long far, unsigned long esr,
> >  	if (!vma)
> >  		goto lock_mmap;
> >
> > +	if ((vm_flags & VM_READ) && (vma->vm_flags & VM_WRITE) &&
> > +	    is_el0_atomic_instr(regs)) {
> > +		vm_flags = VM_WRITE;
> > +		mm_flags |= FAULT_FLAG_WRITE;
> > +	}
>
> The patch looks fine now and AFAICT there's no ABI change.
>
> However, before deciding whether to merge this patch, I'd like to
> understand why OpenJDK cannot use madvise(MADV_POPULATE_WRITE). This
> would be the portable (Linux) solution that works better on
> architectures without such atomic instructions (e.g. arm64 without LSE
> atomics). So fixing user-space would be my preferred solution.

Doing so would be requesting application code changes that are linux 
and ARM64 specific from applications running on Linux. A lot of these are 
proprietary.