| Message ID | 20191113042710.3997854-9-jhubbard@nvidia.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | mm/gup: track dma-pinned pages: FOLL_PIN, FOLL_LONGTERM | expand |
On Tue, Nov 12, 2019 at 08:26:55PM -0800, John Hubbard wrote: > As it says in the updated comment in gup.c: current FOLL_LONGTERM > behavior is incompatible with FAULT_FLAG_ALLOW_RETRY because of the > FS DAX check requirement on vmas. > > However, the corresponding restriction in get_user_pages_remote() was > slightly stricter than is actually required: it forbade all > FOLL_LONGTERM callers, but we can actually allow FOLL_LONGTERM callers > that do not set the "locked" arg. > > Update the code and comments accordingly, and update the VFIO caller > to take advantage of this, fixing a bug as a result: the VFIO caller > is logically a FOLL_LONGTERM user. > > Also, remove an unnessary pair of calls that were releasing and > reacquiring the mmap_sem. There is no need to avoid holding mmap_sem > just in order to call page_to_pfn(). > > Also, move the DAX check ("if a VMA is DAX, don't allow long term > pinning") from the VFIO call site, all the way into the internals > of get_user_pages_remote() and __gup_longterm_locked(). That is: > get_user_pages_remote() calls __gup_longterm_locked(), which in turn > calls check_dax_vmas(). It's lightly explained in the comments as well. > > Thanks to Jason Gunthorpe for pointing out a clean way to fix this, > and to Dan Williams for helping clarify the DAX refactoring. > > Suggested-by: Jason Gunthorpe <jgg@ziepe.ca> > Cc: Dan Williams <dan.j.williams@intel.com> > Cc: Jerome Glisse <jglisse@redhat.com> > Cc: Ira Weiny <ira.weiny@intel.com> > Signed-off-by: John Hubbard <jhubbard@nvidia.com> > drivers/vfio/vfio_iommu_type1.c | 25 ++----------------------- > mm/gup.c | 27 ++++++++++++++++++++++----- > 2 files changed, 24 insertions(+), 28 deletions(-) > > diff --git a/drivers/vfio/vfio_iommu_type1.c b/drivers/vfio/vfio_iommu_type1.c > index d864277ea16f..7301b710c9a4 100644 > +++ b/drivers/vfio/vfio_iommu_type1.c > @@ -340,7 +340,6 @@ static int vaddr_get_pfn(struct mm_struct *mm, unsigned long vaddr, > { > struct page *page[1]; > struct vm_area_struct *vma; > - struct vm_area_struct *vmas[1]; > unsigned int flags = 0; > int ret; > > @@ -348,33 +347,13 @@ static int vaddr_get_pfn(struct mm_struct *mm, unsigned long vaddr, > flags |= FOLL_WRITE; > > down_read(&mm->mmap_sem); > - if (mm == current->mm) { > - ret = get_user_pages(vaddr, 1, flags | FOLL_LONGTERM, page, > - vmas); > - } else { > - ret = get_user_pages_remote(NULL, mm, vaddr, 1, flags, page, > - vmas, NULL); > - /* > - * The lifetime of a vaddr_get_pfn() page pin is > - * userspace-controlled. In the fs-dax case this could > - * lead to indefinite stalls in filesystem operations. > - * Disallow attempts to pin fs-dax pages via this > - * interface. > - */ > - if (ret > 0 && vma_is_fsdax(vmas[0])) { > - ret = -EOPNOTSUPP; > - put_page(page[0]); > - } > - } > - up_read(&mm->mmap_sem); > - > + ret = get_user_pages_remote(NULL, mm, vaddr, 1, flags | FOLL_LONGTERM, > + page, NULL, NULL); > if (ret == 1) { > *pfn = page_to_pfn(page[0]); > return 0; Mind the return with the lock held this needs some goto unwind Jason
On Tue, Nov 12, 2019 at 08:26:55PM -0800, John Hubbard wrote: > As it says in the updated comment in gup.c: current FOLL_LONGTERM > behavior is incompatible with FAULT_FLAG_ALLOW_RETRY because of the > FS DAX check requirement on vmas. > > However, the corresponding restriction in get_user_pages_remote() was > slightly stricter than is actually required: it forbade all > FOLL_LONGTERM callers, but we can actually allow FOLL_LONGTERM callers > that do not set the "locked" arg. > > Update the code and comments accordingly, and update the VFIO caller > to take advantage of this, fixing a bug as a result: the VFIO caller > is logically a FOLL_LONGTERM user. > > Also, remove an unnessary pair of calls that were releasing and > reacquiring the mmap_sem. There is no need to avoid holding mmap_sem > just in order to call page_to_pfn(). > > Also, move the DAX check ("if a VMA is DAX, don't allow long term > pinning") from the VFIO call site, all the way into the internals > of get_user_pages_remote() and __gup_longterm_locked(). That is: > get_user_pages_remote() calls __gup_longterm_locked(), which in turn > calls check_dax_vmas(). It's lightly explained in the comments as well. > > Thanks to Jason Gunthorpe for pointing out a clean way to fix this, > and to Dan Williams for helping clarify the DAX refactoring. > > Suggested-by: Jason Gunthorpe <jgg@ziepe.ca> > Cc: Dan Williams <dan.j.williams@intel.com> > Cc: Jerome Glisse <jglisse@redhat.com> > Cc: Ira Weiny <ira.weiny@intel.com> Reviewed-by: Ira Weiny <ira.weiny@intel.com> > Signed-off-by: John Hubbard <jhubbard@nvidia.com> > --- > drivers/vfio/vfio_iommu_type1.c | 25 ++----------------------- > mm/gup.c | 27 ++++++++++++++++++++++----- > 2 files changed, 24 insertions(+), 28 deletions(-) > > diff --git a/drivers/vfio/vfio_iommu_type1.c b/drivers/vfio/vfio_iommu_type1.c > index d864277ea16f..7301b710c9a4 100644 > --- a/drivers/vfio/vfio_iommu_type1.c > +++ b/drivers/vfio/vfio_iommu_type1.c > @@ -340,7 +340,6 @@ static int vaddr_get_pfn(struct mm_struct *mm, unsigned long vaddr, > { > struct page *page[1]; > struct vm_area_struct *vma; > - struct vm_area_struct *vmas[1]; > unsigned int flags = 0; > int ret; > > @@ -348,33 +347,13 @@ static int vaddr_get_pfn(struct mm_struct *mm, unsigned long vaddr, > flags |= FOLL_WRITE; > > down_read(&mm->mmap_sem); > - if (mm == current->mm) { > - ret = get_user_pages(vaddr, 1, flags | FOLL_LONGTERM, page, > - vmas); > - } else { > - ret = get_user_pages_remote(NULL, mm, vaddr, 1, flags, page, > - vmas, NULL); > - /* > - * The lifetime of a vaddr_get_pfn() page pin is > - * userspace-controlled. In the fs-dax case this could > - * lead to indefinite stalls in filesystem operations. > - * Disallow attempts to pin fs-dax pages via this > - * interface. > - */ > - if (ret > 0 && vma_is_fsdax(vmas[0])) { > - ret = -EOPNOTSUPP; > - put_page(page[0]); > - } > - } > - up_read(&mm->mmap_sem); > - > + ret = get_user_pages_remote(NULL, mm, vaddr, 1, flags | FOLL_LONGTERM, > + page, NULL, NULL); > if (ret == 1) { > *pfn = page_to_pfn(page[0]); > return 0; > } > > - down_read(&mm->mmap_sem); > - > vaddr = untagged_addr(vaddr); > > vma = find_vma_intersection(mm, vaddr, vaddr + 1); > diff --git a/mm/gup.c b/mm/gup.c > index 933524de6249..83702b2e86c8 100644 > --- a/mm/gup.c > +++ b/mm/gup.c > @@ -29,6 +29,13 @@ struct follow_page_context { > unsigned int page_mask; > }; > > +static __always_inline long __gup_longterm_locked(struct task_struct *tsk, > + struct mm_struct *mm, > + unsigned long start, > + unsigned long nr_pages, > + struct page **pages, > + struct vm_area_struct **vmas, > + unsigned int flags); > /* > * Return the compound head page with ref appropriately incremented, > * or NULL if that failed. > @@ -1167,13 +1174,23 @@ long get_user_pages_remote(struct task_struct *tsk, struct mm_struct *mm, > struct vm_area_struct **vmas, int *locked) > { > /* > - * FIXME: Current FOLL_LONGTERM behavior is incompatible with > + * Parts of FOLL_LONGTERM behavior are incompatible with > * FAULT_FLAG_ALLOW_RETRY because of the FS DAX check requirement on > - * vmas. As there are no users of this flag in this call we simply > - * disallow this option for now. > + * vmas. However, this only comes up if locked is set, and there are > + * callers that do request FOLL_LONGTERM, but do not set locked. So, > + * allow what we can. > */ > - if (WARN_ON_ONCE(gup_flags & FOLL_LONGTERM)) > - return -EINVAL; > + if (gup_flags & FOLL_LONGTERM) { > + if (WARN_ON_ONCE(locked)) > + return -EINVAL; > + /* > + * This will check the vmas (even if our vmas arg is NULL) > + * and return -ENOTSUPP if DAX isn't allowed in this case: > + */ > + return __gup_longterm_locked(tsk, mm, start, nr_pages, pages, > + vmas, gup_flags | FOLL_TOUCH | > + FOLL_REMOTE); > + } > > return __get_user_pages_locked(tsk, mm, start, nr_pages, pages, vmas, > locked, > -- > 2.24.0 >
On Wed, Nov 13, 2019 at 09:02:02AM -0400, Jason Gunthorpe wrote: > On Tue, Nov 12, 2019 at 08:26:55PM -0800, John Hubbard wrote: > > As it says in the updated comment in gup.c: current FOLL_LONGTERM > > behavior is incompatible with FAULT_FLAG_ALLOW_RETRY because of the > > FS DAX check requirement on vmas. > > > > However, the corresponding restriction in get_user_pages_remote() was > > slightly stricter than is actually required: it forbade all > > FOLL_LONGTERM callers, but we can actually allow FOLL_LONGTERM callers > > that do not set the "locked" arg. > > > > Update the code and comments accordingly, and update the VFIO caller > > to take advantage of this, fixing a bug as a result: the VFIO caller > > is logically a FOLL_LONGTERM user. > > > > Also, remove an unnessary pair of calls that were releasing and > > reacquiring the mmap_sem. There is no need to avoid holding mmap_sem > > just in order to call page_to_pfn(). > > > > Also, move the DAX check ("if a VMA is DAX, don't allow long term > > pinning") from the VFIO call site, all the way into the internals > > of get_user_pages_remote() and __gup_longterm_locked(). That is: > > get_user_pages_remote() calls __gup_longterm_locked(), which in turn > > calls check_dax_vmas(). It's lightly explained in the comments as well. > > > > Thanks to Jason Gunthorpe for pointing out a clean way to fix this, > > and to Dan Williams for helping clarify the DAX refactoring. > > > > Suggested-by: Jason Gunthorpe <jgg@ziepe.ca> > > Cc: Dan Williams <dan.j.williams@intel.com> > > Cc: Jerome Glisse <jglisse@redhat.com> > > Cc: Ira Weiny <ira.weiny@intel.com> > > Signed-off-by: John Hubbard <jhubbard@nvidia.com> > > drivers/vfio/vfio_iommu_type1.c | 25 ++----------------------- > > mm/gup.c | 27 ++++++++++++++++++++++----- > > 2 files changed, 24 insertions(+), 28 deletions(-) > > > > diff --git a/drivers/vfio/vfio_iommu_type1.c b/drivers/vfio/vfio_iommu_type1.c > > index d864277ea16f..7301b710c9a4 100644 > > +++ b/drivers/vfio/vfio_iommu_type1.c > > @@ -340,7 +340,6 @@ static int vaddr_get_pfn(struct mm_struct *mm, unsigned long vaddr, > > { > > struct page *page[1]; > > struct vm_area_struct *vma; > > - struct vm_area_struct *vmas[1]; > > unsigned int flags = 0; > > int ret; > > > > @@ -348,33 +347,13 @@ static int vaddr_get_pfn(struct mm_struct *mm, unsigned long vaddr, > > flags |= FOLL_WRITE; > > > > down_read(&mm->mmap_sem); > > - if (mm == current->mm) { > > - ret = get_user_pages(vaddr, 1, flags | FOLL_LONGTERM, page, > > - vmas); > > - } else { > > - ret = get_user_pages_remote(NULL, mm, vaddr, 1, flags, page, > > - vmas, NULL); > > - /* > > - * The lifetime of a vaddr_get_pfn() page pin is > > - * userspace-controlled. In the fs-dax case this could > > - * lead to indefinite stalls in filesystem operations. > > - * Disallow attempts to pin fs-dax pages via this > > - * interface. > > - */ > > - if (ret > 0 && vma_is_fsdax(vmas[0])) { > > - ret = -EOPNOTSUPP; > > - put_page(page[0]); > > - } > > - } > > - up_read(&mm->mmap_sem); > > - > > + ret = get_user_pages_remote(NULL, mm, vaddr, 1, flags | FOLL_LONGTERM, > > + page, NULL, NULL); > > if (ret == 1) { > > *pfn = page_to_pfn(page[0]); > > return 0; > > Mind the return with the lock held this needs some goto unwind Ah yea... retract my reviewed by... :-( Ira
On 11/13/19 11:17 AM, Ira Weiny wrote: ... >>> @@ -348,33 +347,13 @@ static int vaddr_get_pfn(struct mm_struct *mm, unsigned long vaddr, >>> flags |= FOLL_WRITE; >>> >>> down_read(&mm->mmap_sem); >>> - if (mm == current->mm) { >>> - ret = get_user_pages(vaddr, 1, flags | FOLL_LONGTERM, page, >>> - vmas); >>> - } else { >>> - ret = get_user_pages_remote(NULL, mm, vaddr, 1, flags, page, >>> - vmas, NULL); >>> - /* >>> - * The lifetime of a vaddr_get_pfn() page pin is >>> - * userspace-controlled. In the fs-dax case this could >>> - * lead to indefinite stalls in filesystem operations. >>> - * Disallow attempts to pin fs-dax pages via this >>> - * interface. >>> - */ >>> - if (ret > 0 && vma_is_fsdax(vmas[0])) { >>> - ret = -EOPNOTSUPP; >>> - put_page(page[0]); >>> - } >>> - } >>> - up_read(&mm->mmap_sem); >>> - >>> + ret = get_user_pages_remote(NULL, mm, vaddr, 1, flags | FOLL_LONGTERM, >>> + page, NULL, NULL); >>> if (ret == 1) { >>> *pfn = page_to_pfn(page[0]); >>> return 0; >> >> Mind the return with the lock held this needs some goto unwind > > Ah yea... retract my reviewed by... :-( > ooops, embarrassed that I missed that, good catch. Will repost with it fixed. thanks,
diff --git a/drivers/vfio/vfio_iommu_type1.c b/drivers/vfio/vfio_iommu_type1.c index d864277ea16f..7301b710c9a4 100644 --- a/drivers/vfio/vfio_iommu_type1.c +++ b/drivers/vfio/vfio_iommu_type1.c @@ -340,7 +340,6 @@ static int vaddr_get_pfn(struct mm_struct *mm, unsigned long vaddr, { struct page *page[1]; struct vm_area_struct *vma; - struct vm_area_struct *vmas[1]; unsigned int flags = 0; int ret; @@ -348,33 +347,13 @@ static int vaddr_get_pfn(struct mm_struct *mm, unsigned long vaddr, flags |= FOLL_WRITE; down_read(&mm->mmap_sem); - if (mm == current->mm) { - ret = get_user_pages(vaddr, 1, flags | FOLL_LONGTERM, page, - vmas); - } else { - ret = get_user_pages_remote(NULL, mm, vaddr, 1, flags, page, - vmas, NULL); - /* - * The lifetime of a vaddr_get_pfn() page pin is - * userspace-controlled. In the fs-dax case this could - * lead to indefinite stalls in filesystem operations. - * Disallow attempts to pin fs-dax pages via this - * interface. - */ - if (ret > 0 && vma_is_fsdax(vmas[0])) { - ret = -EOPNOTSUPP; - put_page(page[0]); - } - } - up_read(&mm->mmap_sem); - + ret = get_user_pages_remote(NULL, mm, vaddr, 1, flags | FOLL_LONGTERM, + page, NULL, NULL); if (ret == 1) { *pfn = page_to_pfn(page[0]); return 0; } - down_read(&mm->mmap_sem); - vaddr = untagged_addr(vaddr); vma = find_vma_intersection(mm, vaddr, vaddr + 1); diff --git a/mm/gup.c b/mm/gup.c index 933524de6249..83702b2e86c8 100644 --- a/mm/gup.c +++ b/mm/gup.c @@ -29,6 +29,13 @@ struct follow_page_context { unsigned int page_mask; }; +static __always_inline long __gup_longterm_locked(struct task_struct *tsk, + struct mm_struct *mm, + unsigned long start, + unsigned long nr_pages, + struct page **pages, + struct vm_area_struct **vmas, + unsigned int flags); /* * Return the compound head page with ref appropriately incremented, * or NULL if that failed. @@ -1167,13 +1174,23 @@ long get_user_pages_remote(struct task_struct *tsk, struct mm_struct *mm, struct vm_area_struct **vmas, int *locked) { /* - * FIXME: Current FOLL_LONGTERM behavior is incompatible with + * Parts of FOLL_LONGTERM behavior are incompatible with * FAULT_FLAG_ALLOW_RETRY because of the FS DAX check requirement on - * vmas. As there are no users of this flag in this call we simply - * disallow this option for now. + * vmas. However, this only comes up if locked is set, and there are + * callers that do request FOLL_LONGTERM, but do not set locked. So, + * allow what we can. */ - if (WARN_ON_ONCE(gup_flags & FOLL_LONGTERM)) - return -EINVAL; + if (gup_flags & FOLL_LONGTERM) { + if (WARN_ON_ONCE(locked)) + return -EINVAL; + /* + * This will check the vmas (even if our vmas arg is NULL) + * and return -ENOTSUPP if DAX isn't allowed in this case: + */ + return __gup_longterm_locked(tsk, mm, start, nr_pages, pages, + vmas, gup_flags | FOLL_TOUCH | + FOLL_REMOTE); + } return __get_user_pages_locked(tsk, mm, start, nr_pages, pages, vmas, locked,
As it says in the updated comment in gup.c: current FOLL_LONGTERM behavior is incompatible with FAULT_FLAG_ALLOW_RETRY because of the FS DAX check requirement on vmas. However, the corresponding restriction in get_user_pages_remote() was slightly stricter than is actually required: it forbade all FOLL_LONGTERM callers, but we can actually allow FOLL_LONGTERM callers that do not set the "locked" arg. Update the code and comments accordingly, and update the VFIO caller to take advantage of this, fixing a bug as a result: the VFIO caller is logically a FOLL_LONGTERM user. Also, remove an unnessary pair of calls that were releasing and reacquiring the mmap_sem. There is no need to avoid holding mmap_sem just in order to call page_to_pfn(). Also, move the DAX check ("if a VMA is DAX, don't allow long term pinning") from the VFIO call site, all the way into the internals of get_user_pages_remote() and __gup_longterm_locked(). That is: get_user_pages_remote() calls __gup_longterm_locked(), which in turn calls check_dax_vmas(). It's lightly explained in the comments as well. Thanks to Jason Gunthorpe for pointing out a clean way to fix this, and to Dan Williams for helping clarify the DAX refactoring. Suggested-by: Jason Gunthorpe <jgg@ziepe.ca> Cc: Dan Williams <dan.j.williams@intel.com> Cc: Jerome Glisse <jglisse@redhat.com> Cc: Ira Weiny <ira.weiny@intel.com> Signed-off-by: John Hubbard <jhubbard@nvidia.com> --- drivers/vfio/vfio_iommu_type1.c | 25 ++----------------------- mm/gup.c | 27 ++++++++++++++++++++++----- 2 files changed, 24 insertions(+), 28 deletions(-)