__filemap_get_folio_mpol() is parametrized by a bunch of GFP flags, which adds complexity for the reader. Since guest_memfd doesn't meaningfully use any of the other FGP flags, undo that complexity by directly calling filemap_alloc_folio().
Directly calling filemap_alloc_folio() also allows the order of 0 to be explicitly specified, which is the only order guest_memfd supports. This is easier to understand, and removes the chance of anything else being able to unintentionally influence allocated folio size. Signed-off-by: Ackerley Tng <[email protected]> --- virt/kvm/guest_memfd.c | 51 +++++++++++++++++++++++++++++------------- 1 file changed, 36 insertions(+), 15 deletions(-) diff --git a/virt/kvm/guest_memfd.c b/virt/kvm/guest_memfd.c index 2df27b6443115..2488d7b8f2b0d 100644 --- a/virt/kvm/guest_memfd.c +++ b/virt/kvm/guest_memfd.c @@ -107,6 +107,39 @@ static int kvm_gmem_prepare_folio(struct kvm *kvm, struct kvm_memory_slot *slot, return __kvm_gmem_prepare_folio(kvm, slot, index, folio); } +static struct folio *__kvm_gmem_get_folio(struct inode *inode, pgoff_t index) +{ + /* TODO: Support huge pages. */ + struct mempolicy *policy; + struct folio *folio; + gfp_t gfp; + int ret; + + /* + * Fast-path: See if folio is already present in mapping to avoid + * policy_lookup. + */ + folio = filemap_lock_folio(inode->i_mapping, index); + if (!IS_ERR(folio)) + return folio; + + gfp = mapping_gfp_mask(inode->i_mapping); + + policy = mpol_shared_policy_lookup(&GMEM_I(inode)->policy, index); + folio = filemap_alloc_folio(gfp, 0, policy); + mpol_cond_put(policy); + if (!folio) + return ERR_PTR(-ENOMEM); + + ret = filemap_add_folio(inode->i_mapping, folio, index, gfp); + if (ret) { + folio_put(folio); + return ERR_PTR(ret); + } + + return folio; +} + /* * Returns a locked folio on success. The caller is responsible for * setting the up-to-date flag before the memory is mapped into the guest. @@ -118,23 +151,11 @@ static int kvm_gmem_prepare_folio(struct kvm *kvm, struct kvm_memory_slot *slot, */ static struct folio *kvm_gmem_get_folio(struct inode *inode, pgoff_t index) { - /* TODO: Support huge pages. */ - struct mempolicy *policy; struct folio *folio; - /* - * Fast-path: See if folio is already present in mapping to avoid - * policy_lookup. - */ - folio = filemap_lock_folio(inode->i_mapping, 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); - mpol_cond_put(policy); + do { + folio = __kvm_gmem_get_folio(inode, index); + } while (PTR_ERR(folio) == -EEXIST); /* * External interfaces like kvm_gmem_get_pfn() support dealing -- 2.53.0.345.g96ddfc5eaa-goog
