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 <kalya...@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);
--
2.47.1
