do_set_mempolicy() builds a validated policy and installs it into the current running task.
An in-kernel user that wants to construct a mempolicy wants the same validation without the install step. Add mempolicy_create(mode, flags, nodes): it allocates the policy and contextualises it against the calling task's cpuset, and returns the mempolicy to the caller (or ERR_PTR on error). do_set_mempolicy() is deliberately left alone rather than reimplemented on top of it. For syscall users, mpol_set_nodemask() and the current task policy swap must run under the task_lock(current) acquisition. Export the symbol to kvm for use in guest_memfd integration. Signed-off-by: Gregory Price <[email protected]> --- include/linux/mempolicy.h | 3 +++ mm/mempolicy.c | 40 ++++++++++++++++++++++++++++++++++++++- 2 files changed, 42 insertions(+), 1 deletion(-) diff --git a/include/linux/mempolicy.h b/include/linux/mempolicy.h index 65c732d440d2f..aef018ad92317 100644 --- a/include/linux/mempolicy.h +++ b/include/linux/mempolicy.h @@ -128,6 +128,9 @@ void mpol_free_shared_policy(struct shared_policy *sp); struct mempolicy *mpol_shared_policy_lookup(struct shared_policy *sp, pgoff_t idx); +struct mempolicy *mempolicy_create(unsigned short mode, unsigned short flags, + nodemask_t *nodes); + struct mempolicy *get_task_policy(struct task_struct *p); struct mempolicy *__get_vma_policy(struct vm_area_struct *vma, unsigned long addr, pgoff_t *ilx); diff --git a/mm/mempolicy.c b/mm/mempolicy.c index 2ad0a5f18280a..da133ffe0b1c8 100644 --- a/mm/mempolicy.c +++ b/mm/mempolicy.c @@ -1085,7 +1085,45 @@ static int mbind_range(struct vma_iterator *vmi, struct vm_area_struct *vma, return vma_replace_policy(vma, new_pol); } -/* Set the process memory policy */ +/** + * mempolicy_create - build a validated, cpuset-contextualised mempolicy + * @mode: MPOL_* mode + * @flags: MPOL_F_* flags + * @nodes: target nodemask, or NULL (interpreted per @mode; see mpol_new()) + * + * Creates a new policy and constrains it to the task's cpuset. + * + * The caller owns the returned reference and frees it with mpol_put(). + * + * Return: the policy (NULL for a default policy), or an ERR_PTR on failure. + */ +struct mempolicy *mempolicy_create(unsigned short mode, unsigned short flags, + nodemask_t *nodes) +{ + struct mempolicy *pol; + NODEMASK_SCRATCH(scratch); + int err; + + if (!scratch) + return ERR_PTR(-ENOMEM); + + pol = mpol_new(mode, flags, nodes); + if (IS_ERR(pol)) + goto out; + + task_lock(current); + err = mpol_set_nodemask(pol, nodes, scratch); + task_unlock(current); + if (err) { + mpol_put(pol); + pol = ERR_PTR(err); + } +out: + NODEMASK_SCRATCH_FREE(scratch); + return pol; +} +EXPORT_SYMBOL_FOR_MODULES(mempolicy_create, "kvm"); + static long do_set_mempolicy(unsigned short mode, unsigned short flags, nodemask_t *nodes) { -- 2.53.0-Meta
