On Fri, Sep 26, 2025 at 12:36:27PM -0700, Sean Christopherson via Linux-f2fs-devel wrote:
static struct mempolicy *kvm_gmem_get_policy(struct vm_area_struct *vma, unsigned long addr, pgoff_t *pgoff) { *pgoff = vma->vm_pgoff + ((addr - vma->vm_start) >> PAGE_SHIFT);
return __kvm_gmem_get_policy(GMEM_I(file_inode(vma->vm_file)), *pgoff);
Argh!!!!! This breaks the selftest because do_get_mempolicy() very specifically falls back to the default_policy, NOT to the current task's policy. That is *exactly* the type of subtle detail that needs to be commented, because there's no way some random KVM developer is going to know that returning NULL here is important with respect to get_mempolicy() ABI.
Do_get_mempolicy was designed to be accessed by the syscall, not as an in-kernel ABI.
get_task_policy also returns the default policy if there's nothing there, because that's what applies.
I have dangerous questions:
why is __kvm_gmem_get_policy using mpol_shared_policy_lookup() instead of get_vma_policy()
get_vma_policy does this all for you
struct mempolicy *get_vma_policy(struct vm_area_struct *vma, unsigned long addr, int order, pgoff_t *ilx) { struct mempolicy *pol;
pol = __get_vma_policy(vma, addr, ilx); if (!pol) pol = get_task_policy(current); if (pol->mode == MPOL_INTERLEAVE || pol->mode == MPOL_WEIGHTED_INTERLEAVE) { *ilx += vma->vm_pgoff >> order; *ilx += (addr - vma->vm_start) >> (PAGE_SHIFT + order); } return pol; }
Of course you still have the same issue: get_task_policy will return the default, because that's what applies.
do_get_mempolicy just seems like the completely incorrect interface to be using here.
~Gregory