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David Alan Gilbert" , David Rientjes , Oliver Upton Subject: Re: [PATCH v3 7/9] userfaultfd: add UFFDIO_CONTINUE ioctl Message-ID: <20210201192120.GG260413@xz-x1> References: <20210128224819.2651899-1-axelrasmussen@google.com> <20210128224819.2651899-8-axelrasmussen@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20210128224819.2651899-8-axelrasmussen@google.com> Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org On Thu, Jan 28, 2021 at 02:48:17PM -0800, Axel Rasmussen wrote: > diff --git a/include/linux/hugetlb.h b/include/linux/hugetlb.h > index f94a35296618..79e1f0155afa 100644 > --- a/include/linux/hugetlb.h > +++ b/include/linux/hugetlb.h > @@ -135,11 +135,14 @@ void hugetlb_show_meminfo(void); > unsigned long hugetlb_total_pages(void); > vm_fault_t hugetlb_fault(struct mm_struct *mm, struct vm_area_struct *vma, > unsigned long address, unsigned int flags); > +#ifdef CONFIG_USERFAULTFD I'm confused why this is needed.. hugetlb_mcopy_atomic_pte() should only be called in userfaultfd.c, but if without uffd config set it won't compile either: obj-$(CONFIG_USERFAULTFD) += userfaultfd.o > int hugetlb_mcopy_atomic_pte(struct mm_struct *dst_mm, pte_t *dst_pte, > struct vm_area_struct *dst_vma, > unsigned long dst_addr, > unsigned long src_addr, > + enum mcopy_atomic_mode mode, > struct page **pagep); > +#endif > int hugetlb_reserve_pages(struct inode *inode, long from, long to, > struct vm_area_struct *vma, > vm_flags_t vm_flags); > diff --git a/include/linux/userfaultfd_k.h b/include/linux/userfaultfd_k.h > index fb9abaeb4194..2fcb686211e8 100644 > --- a/include/linux/userfaultfd_k.h > +++ b/include/linux/userfaultfd_k.h > @@ -37,6 +37,22 @@ extern int sysctl_unprivileged_userfaultfd; > > extern vm_fault_t handle_userfault(struct vm_fault *vmf, unsigned long reason); > > +/* > + * The mode of operation for __mcopy_atomic and its helpers. > + * > + * This is almost an implementation detail (mcopy_atomic below doesn't take this > + * as a parameter), but it's exposed here because memory-kind-specific > + * implementations (e.g. hugetlbfs) need to know the mode of operation. > + */ > +enum mcopy_atomic_mode { > + /* A normal copy_from_user into the destination range. */ > + MCOPY_ATOMIC_NORMAL, > + /* Don't copy; map the destination range to the zero page. */ > + MCOPY_ATOMIC_ZEROPAGE, > + /* Just setup the dst_vma, without modifying the underlying page(s). */ > + MCOPY_ATOMIC_CONTINUE, > +}; > + Maybe better to keep this to where it's used, e.g. hugetlb.h where we've defined hugetlb_mcopy_atomic_pte()? [...] > diff --git a/mm/hugetlb.c b/mm/hugetlb.c > index 6f9d8349f818..3d318ef3d180 100644 > --- a/mm/hugetlb.c > +++ b/mm/hugetlb.c > @@ -4647,6 +4647,7 @@ vm_fault_t hugetlb_fault(struct mm_struct *mm, struct vm_area_struct *vma, > return ret; > } > > +#ifdef CONFIG_USERFAULTFD So I feel like you added the header ifdef for this. IMHO we can drop both since that's what we have had. I agree maybe it's better to not compile that without CONFIG_USERFAULTFD but that may worth a standalone patch anyways. > /* > * Used by userfaultfd UFFDIO_COPY. Based on mcopy_atomic_pte with > * modifications for huge pages. > @@ -4656,6 +4657,7 @@ int hugetlb_mcopy_atomic_pte(struct mm_struct *dst_mm, > struct vm_area_struct *dst_vma, > unsigned long dst_addr, > unsigned long src_addr, > + enum mcopy_atomic_mode mode, > struct page **pagep) > { > struct address_space *mapping; > @@ -4668,7 +4670,10 @@ int hugetlb_mcopy_atomic_pte(struct mm_struct *dst_mm, > int ret; > struct page *page; > > - if (!*pagep) { > + mapping = dst_vma->vm_file->f_mapping; > + idx = vma_hugecache_offset(h, dst_vma, dst_addr); > + > + if (!*pagep && mode != MCOPY_ATOMIC_CONTINUE) { > ret = -ENOMEM; > page = alloc_huge_page(dst_vma, dst_addr, 0); > if (IS_ERR(page)) > @@ -4685,6 +4690,12 @@ int hugetlb_mcopy_atomic_pte(struct mm_struct *dst_mm, > /* don't free the page */ > goto out; > } > + } else if (mode == MCOPY_ATOMIC_CONTINUE) { > + ret = -EFAULT; > + page = find_lock_page(mapping, idx); > + *pagep = NULL; > + if (!page) > + goto out; > } else { > page = *pagep; > *pagep = NULL; I would write this as: if (mode == MCOPY_ATOMIC_CONTINUE) ... else if (!*pagep) ... else ... No strong opinion, but that'll look slightly cleaner to me. [...] > @@ -408,7 +407,7 @@ extern ssize_t __mcopy_atomic_hugetlb(struct mm_struct *dst_mm, > unsigned long dst_start, > unsigned long src_start, > unsigned long len, > - bool zeropage); > + enum mcopy_atomic_mode mode); > #endif /* CONFIG_HUGETLB_PAGE */ > > static __always_inline ssize_t mfill_atomic_pte(struct mm_struct *dst_mm, > @@ -417,7 +416,7 @@ static __always_inline ssize_t mfill_atomic_pte(struct mm_struct *dst_mm, > unsigned long dst_addr, > unsigned long src_addr, > struct page **page, > - bool zeropage, > + enum mcopy_atomic_mode mode, > bool wp_copy) > { > ssize_t err; > @@ -433,22 +432,38 @@ static __always_inline ssize_t mfill_atomic_pte(struct mm_struct *dst_mm, > * and not in the radix tree. > */ > if (!(dst_vma->vm_flags & VM_SHARED)) { > - if (!zeropage) > + switch (mode) { > + case MCOPY_ATOMIC_NORMAL: > err = mcopy_atomic_pte(dst_mm, dst_pmd, dst_vma, > dst_addr, src_addr, page, > wp_copy); > - else > + break; > + case MCOPY_ATOMIC_ZEROPAGE: > err = mfill_zeropage_pte(dst_mm, dst_pmd, > dst_vma, dst_addr); > + break; > + /* It only makes sense to CONTINUE for shared memory. */ > + case MCOPY_ATOMIC_CONTINUE: > + err = -EINVAL; > + break; > + } > } else { > VM_WARN_ON_ONCE(wp_copy); > - if (!zeropage) > + switch (mode) { > + case MCOPY_ATOMIC_NORMAL: > err = shmem_mcopy_atomic_pte(dst_mm, dst_pmd, > dst_vma, dst_addr, > src_addr, page); > - else > + break; > + case MCOPY_ATOMIC_ZEROPAGE: > err = shmem_mfill_zeropage_pte(dst_mm, dst_pmd, > dst_vma, dst_addr); > + break; > + case MCOPY_ATOMIC_CONTINUE: > + /* FIXME: Add minor fault interception for shmem. */ > + err = -EINVAL; > + break; > + } > } > > return err; The whole chunk above is not needed for hugetlbfs it seems - I'd avoid touching the anon/shmem code path until it's being supported. What you need is probably set zeropage as below in __mcopy_atomic(): zeropage = (mode == MCOPY_ATOMIC_ZEROPAGE); Before passing it over to mfill_atomic_pte(). As long as we reject UFFDIO_CONTINUE with !hugetlbfs correctly that'll be enough iiuc. Thanks, -- Peter Xu