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 | 64 +++++++++++++++++++++++++++++++++++++++++-
1 file changed, 63 insertions(+), 1 deletion(-)
diff --git a/virt/kvm/guest_memfd.c b/virt/kvm/guest_memfd.c
index 08a6bc7d25b6..1f6f85edace0 100644
--- a/virt/kvm/guest_memfd.c
+++ b/virt/kvm/guest_memfd.c
@@ -379,7 +379,9 @@ static int kvm_gmem_mmap(struct file *file, struct
vm_area_struct *vma)
}
static struct file_operations kvm_gmem_fops = {
- .mmap = kvm_gmem_mmap,
+ .mmap = kvm_gmem_mmap,
+ .llseek = default_llseek,
+ .write_iter = generic_perform_write,
.open = generic_file_open,
.release = kvm_gmem_release,
.fallocate = kvm_gmem_fallocate,
@@ -390,6 +392,63 @@ void kvm_gmem_init(struct module *module)
kvm_gmem_fops.owner = module;
}
+static int kvm_kmem_gmem_write_begin(const struct kiocb *kiocb,
+ struct address_space *mapping,
+ loff_t pos, unsigned len,
+ struct folio **foliop,
+ void **fsdata)
+{
+ struct file *file = kiocb->ki_filp;
+ pgoff_t index = pos >> PAGE_SHIFT;
+ struct folio *folio;
+
+ if (!PAGE_ALIGNED(pos) || len != PAGE_SIZE)
+ return -EINVAL;
+
+ if (pos + len > i_size_read(file_inode(file)))
+ return -EINVAL;
+
+ folio = kvm_gmem_get_folio(file_inode(file), index);
+ if (IS_ERR(folio))
+ return -EFAULT;
+
+ if (WARN_ON_ONCE(folio_test_large(folio))) {
+ folio_unlock(folio);
+ folio_put(folio);
+ return -EFAULT;
+ }
+
+ if (folio_test_uptodate(folio)) {
+ folio_unlock(folio);
+ folio_put(folio);
+ return -ENOSPC;
+ }
+
+ *foliop = folio;
+ return 0;
+}
+
+static int kvm_kmem_gmem_write_end(const struct kiocb *kiocb,
+ struct address_space *mapping,
+ loff_t pos, unsigned len, unsigned copied,
+ struct folio *folio, void *fsdata)
+{
+ int ret;
+
+ if (copied == len) {
+ kvm_gmem_mark_prepared(folio);
+ ret = copied;
+ } else {
+ filemap_remove_folio(folio);
+ ret = 0;
+ }
+
+ folio_unlock(folio);
+ folio_put(folio);
+
+ return ret;
+}
+
static int kvm_gmem_migrate_folio(struct address_space *mapping,
struct folio *dst, struct folio *src,
enum migrate_mode mode)
@@ -442,6 +501,8 @@ static void kvm_gmem_free_folio(struct folio *folio)
static const struct address_space_operations kvm_gmem_aops = {
.dirty_folio = noop_dirty_folio,
+ .write_begin = kvm_kmem_gmem_write_begin,
+ .write_end = kvm_kmem_gmem_write_end,
.migrate_folio = kvm_gmem_migrate_folio,
.error_remove_folio = kvm_gmem_error_folio,
#ifdef CONFIG_HAVE_KVM_ARCH_GMEM_INVALIDATE
@@ -489,6 +550,7 @@ static int __kvm_gmem_create(struct kvm *kvm, loff_t size,
u64 flags)
}
file->f_flags |= O_LARGEFILE;
+ file->f_mode |= FMODE_LSEEK | FMODE_PWRITE;
inode = file->f_inode;
WARN_ON(file->f_mapping != inode->i_mapping);
--
2.50.1
