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

[Catalin Marinas <catalin.marinas@arm.com>]

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.

(I poked some people in Arm working in the area, hopefully I'll get some
more information)

-- 
Catalin