[PATCH RFC v5 21/53] KVM: guest_memfd: Introduce default handlers for content modes

Ackerley Tng via B4 Relay
2026-04-28T23:25:19Z

Currently, when setting memory attributes, KVM provides no guarantees about
the memory contents.

Introduce default handlers for applying memory content modes, which
different architectures should override.

These handlers will be used later to apply memory content modes during set
memory attributes requests.

Signed-off-by: Ackerley Tng <ackerleytng@google.com>
---
include/linux/kvm_host.h | 12 +++++++++
virt/kvm/guest_memfd.c | 66 ++++++++++++++++++++++++++++++++++++++++++++++++
2 files changed, 78 insertions(+)

diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
index f9ea95e33d050..458bad0083c37 100644
--- a/include/linux/kvm_host.h
+++ b/include/linux/kvm_host.h
@@ -741,6 +741,18 @@ static inline u64 kvm_gmem_get_supported_flags(struct kvm *kvm)

return flags;
}
+
+u64 kvm_arch_gmem_supported_content_modes(struct kvm *kvm, bool to_private);
+int kvm_gmem_apply_content_mode_zero(struct inode *inode, pgoff_t start,
+ pgoff_t end);
+int kvm_arch_gmem_apply_content_mode_zero(struct kvm *kvm, struct inode *inode,
+ pgoff_t start, pgoff_t end);
+int kvm_arch_gmem_apply_content_mode_preserve(struct kvm *kvm,
+ struct inode *inode,
+ pgoff_t start, pgoff_t end);
+int kvm_arch_gmem_apply_content_mode_unspecified(struct kvm *kvm,
+ struct inode *inode,
+ pgoff_t start, pgoff_t end);
#endif

#ifndef kvm_arch_has_readonly_mem
diff --git a/virt/kvm/guest_memfd.c b/virt/kvm/guest_memfd.c
index 85e8b3a981307..b0e4bb554cdf3 100644
--- a/virt/kvm/guest_memfd.c
+++ b/virt/kvm/guest_memfd.c
@@ -693,6 +693,72 @@ static void kvm_gmem_invalidate(struct inode *inode, pgoff_t start, pgoff_t end)
static void kvm_gmem_invalidate(struct inode *inode, pgoff_t start, pgoff_t end) {}
#endif

+u64 __weak kvm_arch_gmem_supported_content_modes(struct kvm *kvm, bool to_private)
+{
+ /* Architectures must override with supported modes. */
+ return 0;
+}
+
+int kvm_gmem_apply_content_mode_zero(struct inode *inode, pgoff_t start,
+ pgoff_t end)
+{
+ struct address_space *mapping = inode->i_mapping;
+ struct folio_batch fbatch;
+ int ret = 0;
+ int i;
+
+ folio_batch_init(&fbatch);
+ while (!ret && filemap_get_folios(mapping, &start, end - 1, &fbatch)) {
+ for (i = 0; !ret && i < folio_batch_count(&fbatch); ++i) {
+ struct folio *folio = fbatch.folios[i];
+
+ folio_lock(folio);
+
+ if (folio_test_hwpoison(folio)) {
+ ret = -EHWPOISON;
+ } else {
+ /*
+ * Hard-coding zeroed range since
+ * guest_memfd only supports PAGE_SIZE
+ * folios and start and end have been
+ * checked to be PAGE_SIZE aligned.
+ */
+ WARN_ON_ONCE(folio_test_large(folio));
+ folio_zero_segment(folio, 0, PAGE_SIZE);
+ }
+
+ folio_unlock(folio);
+ }
+
+ folio_batch_release(&fbatch);
+ cond_resched();
+ }
+
+ return ret;
+}
+
+int __weak kvm_arch_gmem_apply_content_mode_unspecified(struct kvm *kvm,
+ struct inode *inode,
+ pgoff_t start,
+ pgoff_t end)
+{
+ return 0;
+}
+
+int __weak kvm_arch_gmem_apply_content_mode_zero(struct kvm *kvm,
+ struct inode *inode,
+ pgoff_t start, pgoff_t end)
+{
+ return kvm_gmem_apply_content_mode_zero(inode, start, end);
+}
+
+int __weak kvm_arch_gmem_apply_content_mode_preserve(struct kvm *kvm,
+ struct inode *inode,
+ pgoff_t start, pgoff_t end)
+{
+ return -EOPNOTSUPP;
+}
+
static int __kvm_gmem_set_attributes(struct inode *inode, pgoff_t start,
size_t nr_pages, uint64_t attrs,
pgoff_t *err_index)

--
2.54.0.545.g6539524ca2-goog