Re: [PATCH 1/2] mm/madvise: introduce PR_MADV_SELF flag to process_madvise()

[Shakeel Butt <shakeel.butt@linux.dev>]

On Mon, Sep 23, 2024 at 05:03:56PM GMT, Lorenzo Stoakes wrote:
[...]
>  SYSCALL_DEFINE5(process_madvise, int, pidfd, const struct iovec __user *, vec,
>  		size_t, vlen, int, behavior, unsigned int, flags)
>  {
> @@ -1486,10 +1509,9 @@ SYSCALL_DEFINE5(process_madvise, int, pidfd, const struct iovec __user *, vec,
>  	struct iov_iter iter;
>  	struct task_struct *task;
>  	struct mm_struct *mm;
> -	size_t total_len;
>  	unsigned int f_flags;
>  
> -	if (flags != 0) {
> +	if (flags & ~PR_MADV_SELF) {
>  		ret = -EINVAL;
>  		goto out;
>  	}
> @@ -1498,13 +1520,26 @@ SYSCALL_DEFINE5(process_madvise, int, pidfd, const struct iovec __user *, vec,
>  	if (ret < 0)
>  		goto out;
>  
> +	/*
> +	 * Perform an madvise operation on the current process. No restrictions
> +	 * need be applied, nor do we need to pin the task or mm_struct.
> +	 */
> +	if (flags & PR_MADV_SELF) {
> +		ret = vector_madvise(current->mm, &iter, behavior);
> +		goto free_iov;
> +	}
> +
>  	task = pidfd_get_task(pidfd, &f_flags);
>  	if (IS_ERR(task)) {
>  		ret = PTR_ERR(task);
>  		goto free_iov;
>  	}
>  
> -	if (!process_madvise_behavior_valid(behavior)) {
> +	/*
> +	 * We need only perform this check if we are attempting to manipulate a
> +	 * remote process's address space.
> +	 */
> +	if (mm != current->mm && !process_madvise_remote_valid(behavior)) {

Move the above check after mm is initialized i.e. mm = mm_access().

Shakeel