On 2/18/21 4:48 PM, Axel Rasmussen wrote:
<snip>
> @@ -401,8 +398,10 @@ vm_fault_t handle_userfault(struct vm_fault *vmf, unsigned long reason)
>
> BUG_ON(ctx->mm != mm);
>
> - VM_BUG_ON(reason & ~(VM_UFFD_MISSING|VM_UFFD_WP));
> - VM_BUG_ON(!(reason & VM_UFFD_MISSING) ^ !!(reason & VM_UFFD_WP));
> + /* Any unrecognized flag is a bug. */
> + VM_BUG_ON(reason & ~__VM_UFFD_FLAGS);
> + /* 0 or > 1 flags set is a bug; we expect exactly 1. */
> + VM_BUG_ON(!reason || !!(reason & (reason - 1)));
I may be confused, but that seems to be checking for a flag value of 1
as opposed to one flag being set?
>
> if (ctx->features & UFFD_FEATURE_SIGBUS)
> goto out;
<snip>
> diff --git a/mm/hugetlb.c b/mm/hugetlb.c
> index 3bfba75f6cbd..0388107da4b1 100644
> --- a/mm/hugetlb.c
> +++ b/mm/hugetlb.c
> @@ -4352,6 +4352,38 @@ static vm_fault_t hugetlb_no_page(struct mm_struct *mm,
> VM_FAULT_SET_HINDEX(hstate_index(h));
> goto backout_unlocked;
> }
> +
> + /* Check for page in userfault range. */
> + if (userfaultfd_minor(vma)) {
> + u32 hash;
> + struct vm_fault vmf = {
> + .vma = vma,
> + .address = haddr,
> + .flags = flags,
> + /*
> + * Hard to debug if it ends up being used by a
> + * callee that assumes something about the
> + * other uninitialized fields... same as in
> + * memory.c
> + */
> + };
> +
> + unlock_page(page);
> +
> + /*
> + * hugetlb_fault_mutex and i_mmap_rwsem must be dropped
> + * before handling userfault. Reacquire after handling
> + * fault to make calling code simpler.
> + */
> +
> + hash = hugetlb_fault_mutex_hash(mapping, idx);
> + mutex_unlock(&hugetlb_fault_mutex_table[hash]);
> + i_mmap_unlock_read(mapping);
> + ret = handle_userfault(&vmf, VM_UFFD_MINOR);
> + i_mmap_lock_read(mapping);
> + mutex_lock(&hugetlb_fault_mutex_table[hash]);
> + goto out;
> + }
> }
>
> /*
>
I'm good with the hugetlb.c changes. Since this in nearly identical to
the other handle_userfault() in this routine, it might be good to create
a common wrapper. But, that is not required.
--
Mike Kravetz
