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SubjectRe: [RFC 06/14] fork: zero vmap stack using clear_page() instead of memset()
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On 11.03.24 г. 18:46 ч., Pasha Tatashin wrote:
> In preporation for dynamic kernel stacks do not zero the whole span of
> the stack, but instead only the pages that are part of the vm_area.
>
> This is because with dynamic stacks we might have only partially
> populated stacks.
>
> Signed-off-by: Pasha Tatashin <pasha.tatashin@soleen.com>
> ---
> kernel/fork.c | 6 ++++--
> 1 file changed, 4 insertions(+), 2 deletions(-)
>
> diff --git a/kernel/fork.c b/kernel/fork.c
> index 6a2f2c85e09f..41e0baee79d2 100644
> --- a/kernel/fork.c
> +++ b/kernel/fork.c
> @@ -263,8 +263,8 @@ static int memcg_charge_kernel_stack(struct vm_struct *vm)
> static int alloc_thread_stack_node(struct task_struct *tsk, int node)
> {
> struct vm_struct *vm_area;
> + int i, j, nr_pages;
> void *stack;
> - int i;
>
> for (i = 0; i < NR_CACHED_STACKS; i++) {
> vm_area = this_cpu_xchg(cached_stacks[i], NULL);
> @@ -282,7 +282,9 @@ static int alloc_thread_stack_node(struct task_struct *tsk, int node)
> stack = kasan_reset_tag(vm_area->addr);
>
> /* Clear stale pointers from reused stack. */
> - memset(stack, 0, THREAD_SIZE);
> + nr_pages = vm_area->nr_pages;
> + for (j = 0; j < nr_pages; j++)
> + clear_page(page_address(vm_area->pages[j]));

Can't this be memset(stack, 0, nr_pages*PAGE_SIZE) ?
>
> tsk->stack_vm_area = vm_area;
> tsk->stack = stack;

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