Re: [PATCH v5 13/18] mm: don't allow huge faults for files with pre content watches

Amir Goldstein
2024-09-05T08:14:15Z

On Wed, Sep 4, 2024 at 10:29 PM Josef Bacik <josef@toxicpanda.com> wrote:
>
> There's nothing stopping us from supporting this, we could simply pass
> the order into the helper and emit the proper length. However currently
> there's no tests to validate this works properly, so disable it until
> there's a desire to support this along with the appropriate tests.
>
> Reviewed-by: Christian Brauner <brauner@kernel.org>
> Signed-off-by: Josef Bacik <josef@toxicpanda.com>

Reviewed-by: Amir Goldstein <amir73il@gmail.com>

Thanks,
Amir.

> ---
> mm/memory.c | 22 ++++++++++++++++++++++
> 1 file changed, 22 insertions(+)
>
> diff --git a/mm/memory.c b/mm/memory.c
> index d10e616d7389..3010bcc5e4f9 100644
> --- a/mm/memory.c
> +++ b/mm/memory.c
> @@ -78,6 +78,7 @@
> #include <linux/ptrace.h>
> #include <linux/vmalloc.h>
> #include <linux/sched/sysctl.h>
> +#include <linux/fsnotify.h>
>
> #include <trace/events/kmem.h>
>
> @@ -5252,8 +5253,17 @@ static vm_fault_t do_numa_page(struct vm_fault *vmf)
> static inline vm_fault_t create_huge_pmd(struct vm_fault *vmf)
> {
> struct vm_area_struct *vma = vmf->vma;
> + struct file *file = vma->vm_file;
> if (vma_is_anonymous(vma))
> return do_huge_pmd_anonymous_page(vmf);
> + /*
> + * Currently we just emit PAGE_SIZE for our fault events, so don't allow
> + * a huge fault if we have a pre content watch on this file. This would
> + * be trivial to support, but there would need to be tests to ensure
> + * this works properly and those don't exist currently.
> + */
> + if (file && fsnotify_file_has_pre_content_watches(file))
> + return VM_FAULT_FALLBACK;
> if (vma->vm_ops->huge_fault)
> return vma->vm_ops->huge_fault(vmf, PMD_ORDER);
> return VM_FAULT_FALLBACK;
> @@ -5263,6 +5273,7 @@ static inline vm_fault_t create_huge_pmd(struct vm_fault *vmf)
> static inline vm_fault_t wp_huge_pmd(struct vm_fault *vmf)
> {
> struct vm_area_struct *vma = vmf->vma;
> + struct file *file = vma->vm_file;
> const bool unshare = vmf->flags & FAULT_FLAG_UNSHARE;
> vm_fault_t ret;
>
> @@ -5277,6 +5288,9 @@ static inline vm_fault_t wp_huge_pmd(struct vm_fault *vmf)
> }
>
> if (vma->vm_flags & (VM_SHARED | VM_MAYSHARE)) {
> + /* See comment in create_huge_pmd. */
> + if (file && fsnotify_file_has_pre_content_watches(file))
> + goto split;
> if (vma->vm_ops->huge_fault) {
> ret = vma->vm_ops->huge_fault(vmf, PMD_ORDER);
> if (!(ret & VM_FAULT_FALLBACK))
> @@ -5296,9 +5310,13 @@ static vm_fault_t create_huge_pud(struct vm_fault *vmf)
> #if defined(CONFIG_TRANSPARENT_HUGEPAGE) && \
> defined(CONFIG_HAVE_ARCH_TRANSPARENT_HUGEPAGE_PUD)
> struct vm_area_struct *vma = vmf->vma;
> + struct file *file = vma->vm_file;
> /* No support for anonymous transparent PUD pages yet */
> if (vma_is_anonymous(vma))
> return VM_FAULT_FALLBACK;
> + /* See comment in create_huge_pmd. */
> + if (file && fsnotify_file_has_pre_content_watches(file))
> + return VM_FAULT_FALLBACK;
> if (vma->vm_ops->huge_fault)
> return vma->vm_ops->huge_fault(vmf, PUD_ORDER);
> #endif /* CONFIG_TRANSPARENT_HUGEPAGE */
> @@ -5310,12 +5328,16 @@ static vm_fault_t wp_huge_pud(struct vm_fault *vmf, pud_t orig_pud)
> #if defined(CONFIG_TRANSPARENT_HUGEPAGE) && \
> defined(CONFIG_HAVE_ARCH_TRANSPARENT_HUGEPAGE_PUD)
> struct vm_area_struct *vma = vmf->vma;
> + struct file *file = vma->vm_file;
> vm_fault_t ret;
>
> /* No support for anonymous transparent PUD pages yet */
> if (vma_is_anonymous(vma))
> goto split;
> if (vma->vm_flags & (VM_SHARED | VM_MAYSHARE)) {
> + /* See comment in create_huge_pmd. */
> + if (file && fsnotify_file_has_pre_content_watches(file))
> + goto split;
> if (vma->vm_ops->huge_fault) {
> ret = vma->vm_ops->huge_fault(vmf, PUD_ORDER);
> if (!(ret & VM_FAULT_FALLBACK))
> --
> 2.43.0
>