Withdrawn: 8263476: NMT: Stack guard pages should not marked as committed

[duke]

On Sun, 16 Jul 2023 17:24:10 GMT, Johan Sjölen <jsjolen at openjdk.org> wrote:

> Hi,
> 
> Previously the stack guard pages were allocated through the use of `os::commit_memory`. The effect of this is that:
> 
> 1. The pages are considered read+write:able on Linux and BSD
> 2. NMT considers this memory to be committed (approx: considered to be backed by RAM)
> 
> Neither of these properties are desirable. We can instead reserve the memory and be done with it. On Linux and BSD this has the effect that the stack guard pages are active slightly earlier than before as memory is reserved with `PROT_NONE`:
> 
> ```c++
> void StackOverflow::create_stack_guard_pages() {
>   if (!os::uses_stack_guard_pages() ||
>       _stack_guard_state != stack_guard_unused ||
>       (DisablePrimordialThreadGuardPages && os::is_primordial_thread())) {
>       log_info(os, thread)("Stack guard page creation for thread "
>                            UINTX_FORMAT " disabled", os::current_thread_id());
>     return;
>   }
>   address low_addr = stack_end();
>   size_t len = stack_guard_zone_size();
> 
>   assert(is_aligned(low_addr, os::vm_page_size()), "Stack base should be the start of a page");
>   assert(is_aligned(len, os::vm_page_size()), "Stack size should be a multiple of page size");
> 
>   int must_commit = os::must_commit_stack_guard_pages(); // (1) Now active at this call
>   // warning("Guarding at " PTR_FORMAT " for len " SIZE_FORMAT "\n", low_addr, len);
> 
>   if (must_commit && !os::create_stack_guard_pages((char *) low_addr, len)) {
>     log_warning(os, thread)("Attempt to allocate stack guard pages failed.");
>     return;
>   }
> 
>   if (os::guard_memory((char *) low_addr, len)) { // (2) Previously active after this call
>     _stack_guard_state = stack_guard_enabled;
>   } else {
>     log_warning(os, thread)("Attempt to protect stack guard pages failed ("
>       PTR_FORMAT "-" PTR_FORMAT ").", p2i(low_addr), p2i(low_addr + len));
>     vm_exit_out_of_memory(len, OOM_MPROTECT_ERROR, "memory to guard stack pages");
>   }
> 
>   log_debug(os, thread)("Thread " UINTX_FORMAT " stack guard pages activated: "
>     PTR_FORMAT "-" PTR_FORMAT ".",
>     os::current_thread_id(), p2i(low_addr), p2i(low_addr + len));
> }
> 
> 
> On Windows `os::reserve_memory` seems to reserve the pages with read+write privileges, so only the NMT accounting is different here.
> 
> I'm opening the PR now, but this change hasn't gone through testing yet. I will update this PR with a comment and edit here when CI is done.
> 
> Thank you for considering this change.
> 
> Regards,
> Johan

This pull request has been closed without being integrated.

-------------

PR: https://git.openjdk.org/jdk/pull/14896