Yan Zhao yan.y.zhao@intel.com writes:
On Tue, Sep 10, 2024 at 11:43:58PM +0000, Ackerley Tng wrote:
guest_memfd files can always be mmap()ed to userspace, but faultability is controlled by an attribute on the inode.
Co-developed-by: Fuad Tabba tabba@google.com Signed-off-by: Fuad Tabba tabba@google.com Co-developed-by: Ackerley Tng ackerleytng@google.com Signed-off-by: Ackerley Tng ackerleytng@google.com
virt/kvm/guest_memfd.c | 46 ++++++++++++++++++++++++++++++++++++++++-- 1 file changed, 44 insertions(+), 2 deletions(-)
diff --git a/virt/kvm/guest_memfd.c b/virt/kvm/guest_memfd.c index b603518f7b62..fc2483e35876 100644 --- a/virt/kvm/guest_memfd.c +++ b/virt/kvm/guest_memfd.c @@ -781,7 +781,8 @@ static long kvm_gmem_punch_hole(struct inode *inode, loff_t offset, loff_t len) {
Hi Ackerley,
If userspace mmaps a guest_memfd to a VA when a GFN range is shared, it looks that even after the GFN range has been successfully converted to private, userspace can still call madvise(mem, size, MADV_REMOVE) on the userspace VA. This action triggers kvm_gmem_punch_hole() and kvm_gmem_invalidate_begin(), which can zap the private GFNs in the EPT.
Is this behavior intended for in-place conversion, and could it potentially lead to private GFN ranges being accidentally zapped from the EPT?
Apologies if I missed any related discussions on this topic.
No worries and thank you for your review! The next revision will not be requiring userspace to do madvise(MADV_REMOVE), because memory could be mapped in multiple processes, so unmapping from the kernel saves the trouble of coordination in userspace between multiple processes.
Thanks Yan
struct list_head *gmem_list = &inode->i_mapping->i_private_list; pgoff_t start = offset >> PAGE_SHIFT;
- pgoff_t end = (offset + len) >> PAGE_SHIFT;
- pgoff_t nr = len >> PAGE_SHIFT;
- pgoff_t end = start + nr; struct kvm_gmem *gmem;
/* @@ -790,6 +791,9 @@ static long kvm_gmem_punch_hole(struct inode *inode, loff_t offset, loff_t len) */ filemap_invalidate_lock(inode->i_mapping);
- /* TODO: Check if even_cows should be 0 or 1 */
- unmap_mapping_range(inode->i_mapping, start, len, 0);
- list_for_each_entry(gmem, gmem_list, entry) kvm_gmem_invalidate_begin(gmem, start, end);