From: Ackerley Tng <[email protected]> If this guest_memfd was created with a provider, use the provider to allocate a folio. For folio-based providers, using guest_memfd's filemap is better because folio->mapping would be guest_memfd's mapping, and so guest_memfd can handle anything that makes decisions based off folio->mapping, like memory_failure().
Going along these lines of using gmem's filemap, passing gmem's filemap for the provider to insert into seems awkward. At least for tmpfs, the insertion function does a lot of stuff and assumes stuff about the filemap being a tmpfs one (completely fair). I think it's better to use gmem's filemap and do charging (memcg) and inode accounting according to guest_memfd's rules though, hence insertion is done within gmem, in a gmem filemap. Going back to folio->mapping pointing to the gmem filemap, we could have special memory failure handling for guest_memfd folios too, if there's some kind of central registry of all PFNs belonging to guest_memfd? There are other usages of folio->mapping, but gmem doesn't participate in those since gmem doesn't do swap, etc now. For non-folio-based providers, here's my suggestion: Don't provide .alloc_folio(), provide some equivalent callback for pfns, track pfns in gmem. The provider can force gmem to return the folios anytime, the .attach() can be bidirectional. Signed-off-by: Ackerley Tng <[email protected]> --- virt/kvm/guest_memfd.c | 44 ++++++++++++++++++++++++++++++++++++++++---- 1 file changed, 40 insertions(+), 4 deletions(-) diff --git a/virt/kvm/guest_memfd.c b/virt/kvm/guest_memfd.c index a13445c26d9d6..5ac2d558c8dd8 100644 --- a/virt/kvm/guest_memfd.c +++ b/virt/kvm/guest_memfd.c @@ -3,6 +3,7 @@ #include <linux/backing-dev.h> #include <linux/falloc.h> #include <linux/fs.h> +#include <linux/guest_memfd.h> #include <linux/kvm_host.h> #include <linux/maple_tree.h> #include <linux/mempolicy.h> @@ -35,6 +36,9 @@ struct gmem_inode { struct inode vfs_inode; struct list_head gmem_file_list; + void *provider; + const struct guest_memfd_provider_operations *provider_ops; + u64 flags; /* * Every index in this inode, whether memory is populated or @@ -50,6 +54,16 @@ static __always_inline struct gmem_inode *GMEM_I(struct inode *inode) return container_of(inode, struct gmem_inode, vfs_inode); } +static inline struct folio *gmem_provider_alloc_folio(struct gmem_inode *gi, + pgoff_t index, + struct mempolicy *mpol) +{ + if (!gi->provider_ops || !gi->provider_ops->alloc_folio) + return ERR_PTR(-EOPNOTSUPP); + + return gi->provider_ops->alloc_folio(gi->provider, index, mpol); +} + #define kvm_gmem_for_each_file(f, inode) \ list_for_each_entry(f, &GMEM_I(inode)->gmem_file_list, entry) @@ -128,6 +142,7 @@ static bool kvm_gmem_range_has_attributes(struct inode *inode, */ static struct folio *kvm_gmem_get_folio(struct inode *inode, pgoff_t index) { + struct gmem_inode *gi = GMEM_I(inode); /* TODO: Support huge pages. */ struct mempolicy *policy; struct folio *folio; @@ -140,10 +155,29 @@ static struct folio *kvm_gmem_get_folio(struct inode *inode, pgoff_t index) if (!IS_ERR(folio)) return folio; - policy = mpol_shared_policy_lookup(&GMEM_I(inode)->policy, index); - folio = __filemap_get_folio_mpol(inode->i_mapping, index, - FGP_LOCK | FGP_CREAT, - mapping_gfp_mask(inode->i_mapping), policy); + policy = mpol_shared_policy_lookup(&gi->policy, index); + /* + * TODO: Refactor the internal PAGE_SIZE gmem could be an internal + * provider with internal provider_ops. + */ + if (gi->provider_ops) { + folio = gmem_provider_alloc_folio(gi, index, policy); + if (!IS_ERR(folio)) { + int r = filemap_add_folio(inode->i_mapping, folio, + index, GFP_KERNEL); + if (r) { + folio_put(folio); + folio = ERR_PTR(r); + } else { + folio_mark_accessed(folio); + } + } + } else { + folio = __filemap_get_folio_mpol(inode->i_mapping, index, + FGP_LOCK | FGP_CREAT, + mapping_gfp_mask(inode->i_mapping), + policy); + } mpol_cond_put(policy); /* @@ -1334,6 +1368,8 @@ static struct inode *kvm_gmem_alloc_inode(struct super_block *sb) mt_init_flags(&gi->attributes, MT_FLAGS_LOCK_EXTERN | MT_FLAGS_USE_RCU); gi->flags = 0; + gi->provider = NULL; + gi->provider_ops = NULL; INIT_LIST_HEAD(&gi->gmem_file_list); return &gi->vfs_inode; } -- 2.56.0.rc1.315.gc6ed9934b7-goog
