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Mon, 28 Sep 2026 10:42:04 -0700 (PDT) Date: Mon, 28 Sep 2026 17:41:20 +0000 In-Reply-To: <20260928174122.3380703-1-smostafa@google.com> Precedence: bulk X-Mailing-List: linux-doc@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 References: <20260928174122.3380703-1-smostafa@google.com> X-Mailer: git-send-email 2.56.0.rc1.315.gc6ed9934b7-goog Message-ID: <20260928174122.3380703-14-smostafa@google.com> Subject: [RFC PATCH 13/15] fork: Implement partial VMAP stack allocation From: Mostafa Saleh To: linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-mm@kvack.org, linux-hardening@vger.kernel.org, linux-rt-devel@lists.linux.dev Cc: corbet@lwn.net, skhan@linuxfoundation.org, rdunlap@infradead.org, catalin.marinas@arm.com, will@kernel.org, mark.rutland@arm.com, akpm@linux-foundation.org, urezki@gmail.com, mingo@redhat.com, peterz@infradead.org, juri.lelli@redhat.com, vincent.guittot@linaro.org, dietmar.eggemann@arm.com, rostedt@goodmis.org, bsegall@google.com, mgorman@suse.de, vschneid@redhat.com, kprateek.nayak@amd.com, kees@kernel.org, david@kernel.org, ljs@kernel.org, liam@infradead.org, vbabka@kernel.org, rppt@kernel.org, surenb@google.com, mhocko@suse.com, gustavoars@kernel.org, bigeasy@linutronix.de, clrkwllms@kernel.org, Mostafa Saleh , Pasha Tatashin , Linus Walleij , David Stevens Content-Type: text/plain; charset="UTF-8" When CONFIG_ARCH_HAS_VARIABLE_STACK_SIZE is enabled, architectures can allocate a VMAP stack that is smaller than the full THREAD_SIZE. This introduces arch abstraction arch_vm_stack_pages() which defaults to THREAD_SIZE / PAGE_SIZE. During stack allocation, the kernel will map only the requested number of pages at the top of the THREAD_SIZE virtual area (as the stack grows down), leaving the bottom unmapped. This saves memory while retaining the same virtual alignment and guard page overflow detection characteristics. Signed-off-by: Pasha Tatashin [Rebased, used vm_area->nr_pages directly in one instance] [Depends on !PREEMPT_RT] Signed-off-by: Linus Walleij [Fix races around accounting] [Use GFP_ATOMIC when executing in the scheduler] [Depend on INIT_STACK_ALL_* config] [Fix bugs in some error paths and edge cases] [Don't cache partially faulted stacks] [Added out-var to tell if address is on target stack] Signed-off-by: David Stevens [Remove dynamic stack related code, and update commit message] [Fix memory leak in error path of alloc_vmap_stack()] and use VM_UNINITIALIZED before installing the pages] Signed-off-by: Mostafa Saleh --- include/linux/thread_info.h | 8 +++++ kernel/fork.c | 68 +++++++++++++++++++++++++++++++++++++ 2 files changed, 76 insertions(+) diff --git a/include/linux/thread_info.h b/include/linux/thread_info.h index 307b8390fc67..8f052ec82402 100644 --- a/include/linux/thread_info.h +++ b/include/linux/thread_info.h @@ -92,6 +92,14 @@ static inline long set_restart_fn(struct restart_block *restart, #define THREAD_ALIGN THREAD_SIZE #endif +/* + * Arch selecting CONFIG_ARCH_HAS_VARIABLE_STACK_SIZE should override this + * with kernel stack size. + */ +#ifndef arch_vm_stack_pages +#define arch_vm_stack_pages() (THREAD_SIZE / PAGE_SIZE) +#endif + #define THREADINFO_GFP (GFP_KERNEL_ACCOUNT | __GFP_ZERO | __GFP_SKIP_KASAN) /* diff --git a/kernel/fork.c b/kernel/fork.c index ca8e68882316..66fbad3d4cbd 100644 --- a/kernel/fork.c +++ b/kernel/fork.c @@ -119,6 +119,8 @@ /* For dup_mmap(). */ #include "../mm/internal.h" +/* For clear_vm_uninitialized_flag(). */ +#include "../mm/vmalloc.h" #include @@ -272,6 +274,71 @@ static bool try_release_thread_stack_to_cache(struct vm_struct *vm_area) return false; } +#ifdef CONFIG_ARCH_HAS_VARIABLE_STACK_SIZE +static struct vm_struct *alloc_vmap_stack(int node) +{ + gfp_t gfp = GFP_VMAP_STACK; + unsigned long addr, end; + struct vm_struct *vm_area; + int err, i; + + vm_area = get_vm_area_node(THREAD_SIZE, THREAD_ALIGN, + VM_MAP | VM_UNINITIALIZED, node, gfp, + __builtin_return_address(0)); + if (!vm_area) + return NULL; + + vm_area->pages = kmalloc_node(sizeof(void *) * (THREAD_SIZE >> PAGE_SHIFT), + gfp, node); + if (!vm_area->pages) + goto cleanup_err; + + for (i = 0; i < arch_vm_stack_pages(); i++) { + vm_area->pages[i] = alloc_pages_node(node, gfp, 0); + if (!vm_area->pages[i]) + goto cleanup_err; + vm_area->nr_pages++; + mod_lruvec_page_state(vm_area->pages[i], NR_VMALLOC, 1); + } + + end = (unsigned long)kasan_reset_tag(vm_area->addr) + THREAD_SIZE; + addr = end - (arch_vm_stack_pages() * PAGE_SIZE); + + err = vmap_pages_range(addr, end, PAGE_KERNEL, vm_area->pages, PAGE_SHIFT); + if (err) + goto cleanup_err; + + clear_vm_uninitialized_flag(vm_area); + return vm_area; + +cleanup_err: + remove_vm_area(vm_area->addr); + if (vm_area->pages) { + for (i = 0; i < vm_area->nr_pages; i++) { + mod_lruvec_page_state(vm_area->pages[i], NR_VMALLOC, -1); + __free_page(vm_area->pages[i]); + } + kfree(vm_area->pages); + } + kfree(vm_area); + return NULL; +} + +static void free_vmap_stack(struct vm_struct *vm_area) +{ + int i; + + remove_vm_area(vm_area->addr); + + for (i = 0; i < vm_area->nr_pages; i++) { + mod_lruvec_page_state(vm_area->pages[i], NR_VMALLOC, -1); + __free_page(vm_area->pages[i]); + } + + kfree(vm_area->pages); + kfree(vm_area); +} +#else static inline struct vm_struct *alloc_vmap_stack(int node) { void *stack; @@ -286,6 +353,7 @@ static inline void free_vmap_stack(struct vm_struct *vm_area) { vfree(vm_area->addr); } +#endif /* CONFIG_ARCH_HAS_VARIABLE_STACK_SIZE */ static void thread_stack_free_work(struct work_struct *work) { -- 2.56.0.rc1.315.gc6ed9934b7-goog