On Mon, Jan 23, 2023 at 06:43:34PM +0300, Kirill A. Shutemov wrote: > On Thu, Dec 22, 2022 at 06:15:24PM +0000, Sean Christopherson wrote: > > On Wed, Dec 21, 2022, Chao Peng wrote: > > > On Tue, Dec 20, 2022 at 08:33:05AM +0000, Huang, Kai wrote: > > > > On Tue, 2022-12-20 at 15:22 +0800, Chao Peng wrote: > > > > > On Mon, Dec 19, 2022 at 08:48:10AM +0000, Huang, Kai wrote: > > > > > > On Mon, 2022-12-19 at 15:53 +0800, Chao Peng wrote: > > > > But for non-restricted-mem case, it is correct for KVM to decrease page's > > > > refcount after setting up mapping in the secondary mmu, otherwise the page will > > > > be pinned by KVM for normal VM (since KVM uses GUP to get the page). > > > > > > That's true. Actually even true for restrictedmem case, most likely we > > > will still need the kvm_release_pfn_clean() for KVM generic code. On one > > > side, other restrictedmem users like pKVM may not require page pinning > > > at all. On the other side, see below. > > > > > > > > > > > So what we are expecting is: for KVM if the page comes from restricted mem, then > > > > KVM cannot decrease the refcount, otherwise for normal page via GUP KVM should. > > > > No, requiring the user (KVM) to guard against lack of support for page migration > > in restricted mem is a terrible API. It's totally fine for restricted mem to not > > support page migration until there's a use case, but punting the problem to KVM > > is not acceptable. Restricted mem itself doesn't yet support page migration, > > e.g. explosions would occur even if KVM wanted to allow migration since there is > > no notification to invalidate existing mappings. > > I tried to find a way to hook into migration path from restrictedmem. It > is not easy because from code-mm PoV the restrictedmem page just yet > another shmem page. > > It is somewhat dubious, but I think it should be safe to override > mapping->a_ops for the shmem mapping. > > It also eliminates need in special treatment for the restrictedmem pages > from memory-failure code. > > shmem_mapping() uses ->a_ops to detect shmem mapping. Modify the > implementation to still be true for restrictedmem pages. > > Build tested only. > > Any comments? Hi Kirill, We've been testing your approach to handle pinning for the SNP+UPM implementation and haven't noticed any problems so far: (based on top of Sean's updated UPM v10 tree) https://github.com/mdroth/linux/commit/f780033e6812a01f8732060605d941474fee2bd6 Prior to your patch we also tried elevating refcount via restrictedmem_get_page() for cases where shmem_get_folio(..., SGP_NOALLOC) indicates the page hasn't been allocated yet, and that approach also seems to work, but there are potential races and other ugliness that make your approach seem a lot cleaner. -Mike > > diff --git a/include/linux/restrictedmem.h b/include/linux/restrictedmem.h > index 6fddb08f03cc..73ded3c3bad1 100644 > --- a/include/linux/restrictedmem.h > +++ b/include/linux/restrictedmem.h > @@ -36,8 +36,6 @@ static inline bool file_is_restrictedmem(struct file *file) > return file->f_inode->i_sb->s_magic == RESTRICTEDMEM_MAGIC; > } > > -void restrictedmem_error_page(struct page *page, struct address_space *mapping); > - > #else > > static inline bool file_is_restrictedmem(struct file *file) > @@ -45,11 +43,6 @@ static inline bool file_is_restrictedmem(struct file *file) > return false; > } > > -static inline void restrictedmem_error_page(struct page *page, > - struct address_space *mapping) > -{ > -} > - > #endif /* CONFIG_RESTRICTEDMEM */ > > #endif /* _LINUX_RESTRICTEDMEM_H */ > diff --git a/include/linux/shmem_fs.h b/include/linux/shmem_fs.h > index d500ea967dc7..a4af160f37e4 100644 > --- a/include/linux/shmem_fs.h > +++ b/include/linux/shmem_fs.h > @@ -9,6 +9,7 @@ > #include <linux/percpu_counter.h> > #include <linux/xattr.h> > #include <linux/fs_parser.h> > +#include <linux/magic.h> > > /* inode in-kernel data */ > > @@ -75,10 +76,9 @@ extern unsigned long shmem_get_unmapped_area(struct file *, unsigned long addr, > unsigned long len, unsigned long pgoff, unsigned long flags); > extern int shmem_lock(struct file *file, int lock, struct ucounts *ucounts); > #ifdef CONFIG_SHMEM > -extern const struct address_space_operations shmem_aops; > static inline bool shmem_mapping(struct address_space *mapping) > { > - return mapping->a_ops == &shmem_aops; > + return mapping->host->i_sb->s_magic == TMPFS_MAGIC; > } > #else > static inline bool shmem_mapping(struct address_space *mapping) > diff --git a/mm/memory-failure.c b/mm/memory-failure.c > index f91b444e471e..145bb561ddb3 100644 > --- a/mm/memory-failure.c > +++ b/mm/memory-failure.c > @@ -62,7 +62,6 @@ > #include <linux/page-isolation.h> > #include <linux/pagewalk.h> > #include <linux/shmem_fs.h> > -#include <linux/restrictedmem.h> > #include "swap.h" > #include "internal.h" > #include "ras/ras_event.h" > @@ -941,8 +940,6 @@ static int me_pagecache_clean(struct page_state *ps, struct page *p) > goto out; > } > > - restrictedmem_error_page(p, mapping); > - > /* > * The shmem page is kept in page cache instead of truncating > * so is expected to have an extra refcount after error-handling. > diff --git a/mm/restrictedmem.c b/mm/restrictedmem.c > index 15c52301eeb9..d0ca609b82cb 100644 > --- a/mm/restrictedmem.c > +++ b/mm/restrictedmem.c > @@ -189,6 +189,51 @@ static struct file *restrictedmem_file_create(struct file *memfd) > return file; > } > > +static int restricted_error_remove_page(struct address_space *mapping, > + struct page *page) > +{ > + struct super_block *sb = restrictedmem_mnt->mnt_sb; > + struct inode *inode, *next; > + pgoff_t start, end; > + > + start = page->index; > + end = start + thp_nr_pages(page); > + > + spin_lock(&sb->s_inode_list_lock); > + list_for_each_entry_safe(inode, next, &sb->s_inodes, i_sb_list) { > + struct restrictedmem *rm = inode->i_mapping->private_data; > + struct restrictedmem_notifier *notifier; > + struct file *memfd = rm->memfd; > + unsigned long index; > + > + if (memfd->f_mapping != mapping) > + continue; > + > + xa_for_each_range(&rm->bindings, index, notifier, start, end) > + notifier->ops->error(notifier, start, end); > + break; > + } > + spin_unlock(&sb->s_inode_list_lock); > + > + return 0; > +} > + > +#ifdef CONFIG_MIGRATION > +static int restricted_folio(struct address_space *mapping, struct folio *dst, > + struct folio *src, enum migrate_mode mode) > +{ > + return -EBUSY; > +} > +#endif > + > +static struct address_space_operations restricted_aops = { > + .dirty_folio = noop_dirty_folio, > + .error_remove_page = restricted_error_remove_page, > +#ifdef CONFIG_MIGRATION > + .migrate_folio = restricted_folio, > +#endif > +}; > + > SYSCALL_DEFINE1(memfd_restricted, unsigned int, flags) > { > struct file *file, *restricted_file; > @@ -209,6 +254,8 @@ SYSCALL_DEFINE1(memfd_restricted, unsigned int, flags) > file->f_mode |= FMODE_LSEEK | FMODE_PREAD | FMODE_PWRITE; > file->f_flags |= O_LARGEFILE; > > + file->f_mapping->a_ops = &restricted_aops; > + > restricted_file = restrictedmem_file_create(file); > if (IS_ERR(restricted_file)) { > err = PTR_ERR(restricted_file); > @@ -293,31 +340,3 @@ int restrictedmem_get_page(struct file *file, pgoff_t offset, > } > EXPORT_SYMBOL_GPL(restrictedmem_get_page); > > -void restrictedmem_error_page(struct page *page, struct address_space *mapping) > -{ > - struct super_block *sb = restrictedmem_mnt->mnt_sb; > - struct inode *inode, *next; > - pgoff_t start, end; > - > - if (!shmem_mapping(mapping)) > - return; > - > - start = page->index; > - end = start + thp_nr_pages(page); > - > - spin_lock(&sb->s_inode_list_lock); > - list_for_each_entry_safe(inode, next, &sb->s_inodes, i_sb_list) { > - struct restrictedmem *rm = inode->i_mapping->private_data; > - struct restrictedmem_notifier *notifier; > - struct file *memfd = rm->memfd; > - unsigned long index; > - > - if (memfd->f_mapping != mapping) > - continue; > - > - xa_for_each_range(&rm->bindings, index, notifier, start, end) > - notifier->ops->error(notifier, start, end); > - break; > - } > - spin_unlock(&sb->s_inode_list_lock); > -} > diff --git a/mm/shmem.c b/mm/shmem.c > index c1d8b8a1aa3b..3df4d95784b9 100644 > --- a/mm/shmem.c > +++ b/mm/shmem.c > @@ -231,7 +231,7 @@ static inline void shmem_inode_unacct_blocks(struct inode *inode, long pages) > } > > static const struct super_operations shmem_ops; > -const struct address_space_operations shmem_aops; > +static const struct address_space_operations shmem_aops; > static const struct file_operations shmem_file_operations; > static const struct inode_operations shmem_inode_operations; > static const struct inode_operations shmem_dir_inode_operations; > @@ -3894,7 +3894,7 @@ static int shmem_error_remove_page(struct address_space *mapping, > return 0; > } > > -const struct address_space_operations shmem_aops = { > +static const struct address_space_operations shmem_aops = { > .writepage = shmem_writepage, > .dirty_folio = noop_dirty_folio, > #ifdef CONFIG_TMPFS > @@ -3906,7 +3906,6 @@ const struct address_space_operations shmem_aops = { > #endif > .error_remove_page = shmem_error_remove_page, > }; > -EXPORT_SYMBOL(shmem_aops); > > static const struct file_operations shmem_file_operations = { > .mmap = shmem_mmap, > -- > Kiryl Shutsemau / Kirill A. Shutemov
