write syscall populates guest_memfd with user-supplied data in a generic way, ie no vendor-specific preparation is performed. This is supposed to be used in non-CoCo setups where guest memory is not hardware-encrypted.
The following behaviour is implemented: - only page-aligned count and offset are allowed - if the memory is already allocated, the call will successfully populate it - if the memory is not allocated, the call will both allocate and populate - if the memory is already populated, the call will not repopulate it
Signed-off-by: Nikita Kalyazin kalyazin@amazon.com --- virt/kvm/guest_memfd.c | 94 ++++++++++++++++++++++++++++++++++++++++-- 1 file changed, 91 insertions(+), 3 deletions(-)
diff --git a/virt/kvm/guest_memfd.c b/virt/kvm/guest_memfd.c index 30b47ff0e6d2..f93fe5835173 100644 --- a/virt/kvm/guest_memfd.c +++ b/virt/kvm/guest_memfd.c @@ -417,12 +417,97 @@ static int kvm_gmem_mmap(struct file *file, struct vm_area_struct *vma)
return 0; } -#else -#define kvm_gmem_mmap NULL + +static ssize_t kvm_kmem_gmem_write(struct file *file, const char __user *buf, + size_t count, loff_t *offset) +{ + pgoff_t start, end, index; + ssize_t ret = 0; + + if (!PAGE_ALIGNED(*offset) || !PAGE_ALIGNED(count)) + return -EINVAL; + + if (*offset + count > i_size_read(file_inode(file))) + return -EINVAL; + + if (!buf) + return -EINVAL; + + start = *offset >> PAGE_SHIFT; + end = (*offset + count) >> PAGE_SHIFT; + + filemap_invalidate_lock_shared(file->f_mapping); + + for (index = start; index < end; ) { + struct folio *folio; + void *vaddr; + pgoff_t buf_offset = (index - start) << PAGE_SHIFT; + + if (signal_pending(current)) { + ret = -EINTR; + goto out; + } + + folio = kvm_gmem_get_folio(file_inode(file), index); + if (IS_ERR(folio)) { + ret = -EFAULT; + goto out; + } + + if (folio_test_hwpoison(folio)) { + folio_unlock(folio); + folio_put(folio); + ret = -EFAULT; + goto out; + } + + /* No support for huge pages. */ + if (WARN_ON_ONCE(folio_test_large(folio))) { + folio_unlock(folio); + folio_put(folio); + ret = -EFAULT; + goto out; + } + + if (folio_test_uptodate(folio)) { + folio_unlock(folio); + folio_put(folio); + ret = -ENOSPC; + goto out; + } + + folio_unlock(folio); + + vaddr = kmap_local_folio(folio, 0); + ret = copy_from_user(vaddr, buf + buf_offset, PAGE_SIZE); + kunmap_local(vaddr); + if (ret) { + ret = -EINVAL; + folio_put(folio); + goto out; + } + + kvm_gmem_mark_prepared(folio); + folio_put(folio); + + index = folio_next_index(folio); + *offset += PAGE_SIZE; + } + +out: + filemap_invalidate_unlock_shared(file->f_mapping); + + return ret && start == (*offset >> PAGE_SHIFT) ? + ret : *offset - (start << PAGE_SHIFT); +} #endif /* CONFIG_KVM_GMEM_SHARED_MEM */
static struct file_operations kvm_gmem_fops = { - .mmap = kvm_gmem_mmap, +#ifdef CONFIG_KVM_GMEM_SHARED_MEM + .mmap = kvm_gmem_mmap, + .llseek = default_llseek, + .write = kvm_kmem_gmem_write, +#endif /* CONFIG_KVM_GMEM_SHARED_MEM */ .open = generic_file_open, .release = kvm_gmem_release, .fallocate = kvm_gmem_fallocate, @@ -538,6 +623,9 @@ static int __kvm_gmem_create(struct kvm *kvm, loff_t size, u64 flags) }
file->f_flags |= O_LARGEFILE; +#ifdef CONFIG_KVM_GMEM_SHARED_MEM + file->f_mode |= FMODE_LSEEK | FMODE_PWRITE; +#endif /* CONFIG_KVM_GMEM_SHARED_MEM */
inode = file->f_inode; WARN_ON(file->f_mapping != inode->i_mapping);