KVM: guest_memfd: make kvm_gmem_prepare_folio() operate on a single struct kvm

This is now possible because preparation is done by kvm_gmem_get_pfn()
instead of fallocate().  In practice this is not a limitation, because
even though guest_memfd can be bound to multiple struct kvm, for
hardware implementations of confidential computing only one guest
(identified by an ASID on SEV-SNP, or an HKID on TDX) will be able
to access it.

In the case of intra-host migration (not implemented yet for SEV-SNP,
but we can use SEV-ES as an idea of how it will work), the new struct
kvm inherits the same ASID and preparation need not be repeated.

Reviewed-by: Michael Roth <michael.roth@amd.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

diff --git a/virt/kvm/guest_memfd.c b/virt/kvm/guest_memfd.c
index 5af278c7adbac78a9f9b3c87c3fa3bb2ae27e3e6..444ded162154fa7f181a58d51aba05a8b82b75fe 100644 (file)
--- a/virt/kvm/guest_memfd.c
+++ b/virt/kvm/guest_memfd.c
@@ -25,37 +25,27 @@ static inline kvm_pfn_t folio_file_pfn(struct folio *folio, pgoff_t index)
        return folio_pfn(folio) + (index & (folio_nr_pages(folio) - 1));
 }
 
-static int __kvm_gmem_prepare_folio(struct inode *inode, pgoff_t index, struct folio *folio)
+static int __kvm_gmem_prepare_folio(struct kvm *kvm, struct kvm_memory_slot *slot,
+                                   pgoff_t index, struct folio *folio)
 {
 #ifdef CONFIG_HAVE_KVM_ARCH_GMEM_PREPARE
-       struct list_head *gmem_list = &inode->i_mapping->i_private_list;
-       struct kvm_gmem *gmem;
+       kvm_pfn_t pfn;
+       gfn_t gfn;
+       int rc;
 
-       list_for_each_entry(gmem, gmem_list, entry) {
-               struct kvm_memory_slot *slot;
-               struct kvm *kvm = gmem->kvm;
-               kvm_pfn_t pfn;
-               gfn_t gfn;
-               int rc;
-
-               if (!kvm_arch_gmem_prepare_needed(kvm))
-                       continue;
-
-               slot = xa_load(&gmem->bindings, index);
-               if (!slot)
-                       continue;
-
-               pfn = folio_file_pfn(folio, index);
-               gfn = slot->base_gfn + index - slot->gmem.pgoff;
-               rc = kvm_arch_gmem_prepare(kvm, gfn, pfn, folio_order(folio));
-               if (rc) {
-                       pr_warn_ratelimited("gmem: Failed to prepare folio for GFN %llx PFN %llx error %d.\n",
-                                           gfn, pfn, rc);
-                       return rc;
-               }
-       }
+       if (!kvm_arch_gmem_prepare_needed(kvm))
+               return 0;
 
+       pfn = folio_file_pfn(folio, index);
+       gfn = slot->base_gfn + index - slot->gmem.pgoff;
+       rc = kvm_arch_gmem_prepare(kvm, gfn, pfn, folio_order(folio));
+       if (rc) {
+               pr_warn_ratelimited("gmem: Failed to prepare folio for index %lx GFN %llx PFN %llx error %d.\n",
+                                   index, gfn, pfn, rc);
+               return rc;
+       }
 #endif
+
        return 0;
 }
 
@@ -65,7 +55,7 @@ static int __kvm_gmem_prepare_folio(struct inode *inode, pgoff_t index, struct f
  * On successful return the guest sees a zero page so as to avoid
  * leaking host data and the up-to-date flag is set.
  */
-static int kvm_gmem_prepare_folio(struct file *file, struct kvm_memory_slot *slot,
+static int kvm_gmem_prepare_folio(struct kvm *kvm, struct kvm_memory_slot *slot,
                                  gfn_t gfn, struct folio *folio)
 {
        unsigned long nr_pages, i;
@@ -95,8 +85,7 @@ static int kvm_gmem_prepare_folio(struct file *file, struct kvm_memory_slot *slo
        WARN_ON(!IS_ALIGNED(slot->gmem.pgoff, 1 << folio_order(folio)));
        index = gfn - slot->base_gfn + slot->gmem.pgoff;
        index = ALIGN_DOWN(index, 1 << folio_order(folio));
-
-       r = __kvm_gmem_prepare_folio(file_inode(file), index, folio);
+       r = __kvm_gmem_prepare_folio(kvm, slot, index, folio);
        if (!r)
                folio_mark_uptodate(folio);
 
@@ -619,7 +608,7 @@ int kvm_gmem_get_pfn(struct kvm *kvm, struct kvm_memory_slot *slot,
                goto out;
        }
 
-       r = kvm_gmem_prepare_folio(file, slot, gfn, folio);
+       r = kvm_gmem_prepare_folio(kvm, slot, gfn, folio);
        folio_unlock(folio);
        if (r < 0)
                folio_put(folio);