The faultability xarray is stored on the inode since faultability is a property of the guest_memfd's memory contents.
In this RFC, presence of an entry in the xarray indicates faultable, but this could be flipped so that presence indicates unfaultable. For flexibility, a special value "FAULT" is used instead of a simple boolean. However, at some stages of a VM's lifecycle there could be more private pages, and at other stages there could be more shared pages. This is likely to be replaced by a better data structure in a future revision to better support ranges. Also store struct kvm_gmem_hugetlb in struct kvm_gmem_hugetlb as a pointer. inode->i_mapping->i_private_data. Co-developed-by: Fuad Tabba <[email protected]> Signed-off-by: Fuad Tabba <[email protected]> Co-developed-by: Ackerley Tng <[email protected]> Signed-off-by: Ackerley Tng <[email protected]> Co-developed-by: Vishal Annapurve <[email protected]> Signed-off-by: Vishal Annapurve <[email protected]> --- virt/kvm/guest_memfd.c | 105 ++++++++++++++++++++++++++++++++++++----- 1 file changed, 94 insertions(+), 11 deletions(-) diff --git a/virt/kvm/guest_memfd.c b/virt/kvm/guest_memfd.c index 8151df2c03e5..b603518f7b62 100644 --- a/virt/kvm/guest_memfd.c +++ b/virt/kvm/guest_memfd.c @@ -26,11 +26,21 @@ struct kvm_gmem_hugetlb { struct hugepage_subpool *spool; }; -static struct kvm_gmem_hugetlb *kvm_gmem_hgmem(struct inode *inode) +struct kvm_gmem_inode_private { + struct xarray faultability; + struct kvm_gmem_hugetlb *hgmem; +}; + +static struct kvm_gmem_inode_private *kvm_gmem_private(struct inode *inode) { return inode->i_mapping->i_private_data; } +static struct kvm_gmem_hugetlb *kvm_gmem_hgmem(struct inode *inode) +{ + return kvm_gmem_private(inode)->hgmem; +} + static bool is_kvm_gmem_hugetlb(struct inode *inode) { u64 flags = (u64)inode->i_private; @@ -38,6 +48,57 @@ static bool is_kvm_gmem_hugetlb(struct inode *inode) return flags & KVM_GUEST_MEMFD_HUGETLB; } +#define KVM_GMEM_FAULTABILITY_VALUE 0x4641554c54 /* FAULT */ + +/** + * Set faultability of given range of inode indices [@start, @end) to + * @faultable. Return 0 if attributes were successfully updated or negative + * errno on error. + */ +static int kvm_gmem_set_faultable(struct inode *inode, pgoff_t start, pgoff_t end, + bool faultable) +{ + struct xarray *faultability; + void *val; + pgoff_t i; + + /* + * The expectation is that fewer pages are faultable, hence save memory + * entries are created for faultable pages as opposed to creating + * entries for non-faultable pages. + */ + val = faultable ? xa_mk_value(KVM_GMEM_FAULTABILITY_VALUE) : NULL; + faultability = &kvm_gmem_private(inode)->faultability; + + /* + * TODO replace this with something else (maybe interval + * tree?). store_range doesn't quite do what we expect if overlapping + * ranges are specified: if we store_range(5, 10, val) and then + * store_range(7, 12, NULL), the entire range [5, 12] will be NULL. For + * now, use the slower xa_store() to store individual entries on indices + * to avoid this. + */ + for (i = start; i < end; i++) { + int r; + + r = xa_err(xa_store(faultability, i, val, GFP_KERNEL_ACCOUNT)); + if (r) + return r; + } + + return 0; +} + +/** + * Return true if the page at @index is allowed to be faulted in. + */ +static bool kvm_gmem_is_faultable(struct inode *inode, pgoff_t index) +{ + struct xarray *faultability = &kvm_gmem_private(inode)->faultability; + + return xa_to_value(xa_load(faultability, index)) == KVM_GMEM_FAULTABILITY_VALUE; +} + /** * folio_file_pfn - like folio_file_page, but return a pfn. * @folio: The folio which contains this index. @@ -895,11 +956,21 @@ static void kvm_gmem_hugetlb_teardown(struct inode *inode) static void kvm_gmem_evict_inode(struct inode *inode) { + struct kvm_gmem_inode_private *private = kvm_gmem_private(inode); + + /* + * .evict_inode can be called before faultability is set up if there are + * issues during inode creation. + */ + if (private) + xa_destroy(&private->faultability); + if (is_kvm_gmem_hugetlb(inode)) kvm_gmem_hugetlb_teardown(inode); else truncate_inode_pages_final(inode->i_mapping); + kfree(private); clear_inode(inode); } @@ -1028,7 +1099,9 @@ static const struct inode_operations kvm_gmem_iops = { .setattr = kvm_gmem_setattr, }; -static int kvm_gmem_hugetlb_setup(struct inode *inode, loff_t size, u64 flags) +static int kvm_gmem_hugetlb_setup(struct inode *inode, + struct kvm_gmem_inode_private *private, + loff_t size, u64 flags) { struct kvm_gmem_hugetlb *hgmem; struct hugepage_subpool *spool; @@ -1036,6 +1109,10 @@ static int kvm_gmem_hugetlb_setup(struct inode *inode, loff_t size, u64 flags) struct hstate *h; long hpages; + hgmem = kzalloc(sizeof(*hgmem), GFP_KERNEL); + if (!hgmem) + return -ENOMEM; + page_size_log = (flags >> KVM_GUEST_MEMFD_HUGE_SHIFT) & KVM_GUEST_MEMFD_HUGE_MASK; h = hstate_sizelog(page_size_log); @@ -1046,21 +1123,16 @@ static int kvm_gmem_hugetlb_setup(struct inode *inode, loff_t size, u64 flags) if (!spool) goto err; - hgmem = kzalloc(sizeof(*hgmem), GFP_KERNEL); - if (!hgmem) - goto err_subpool; - inode->i_blkbits = huge_page_shift(h); hgmem->h = h; hgmem->spool = spool; - inode->i_mapping->i_private_data = hgmem; + private->hgmem = hgmem; return 0; -err_subpool: - kfree(spool); err: + kfree(hgmem); return -ENOMEM; } @@ -1068,6 +1140,7 @@ static struct inode *kvm_gmem_inode_make_secure_inode(const char *name, loff_t size, u64 flags) { const struct qstr qname = QSTR_INIT(name, strlen(name)); + struct kvm_gmem_inode_private *private; struct inode *inode; int err; @@ -1079,12 +1152,20 @@ static struct inode *kvm_gmem_inode_make_secure_inode(const char *name, if (err) goto out; + err = -ENOMEM; + private = kzalloc(sizeof(*private), GFP_KERNEL); + if (!private) + goto out; + if (flags & KVM_GUEST_MEMFD_HUGETLB) { - err = kvm_gmem_hugetlb_setup(inode, size, flags); + err = kvm_gmem_hugetlb_setup(inode, private, size, flags); if (err) - goto out; + goto free_private; } + xa_init(&private->faultability); + inode->i_mapping->i_private_data = private; + inode->i_private = (void *)(unsigned long)flags; inode->i_op = &kvm_gmem_iops; inode->i_mapping->a_ops = &kvm_gmem_aops; @@ -1097,6 +1178,8 @@ static struct inode *kvm_gmem_inode_make_secure_inode(const char *name, return inode; +free_private: + kfree(private); out: iput(inode); -- 2.46.0.598.g6f2099f65c-goog
