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

From: Christoph Lameter (Ampere)
Date: Fri Jun 28 2024 - 12:57:52 EST


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.