[PATCH 07/12] KVM: guest_memfd: make kvm_gmem_prepare_folio() operate on a single struct kvm

Paolo Bonzini
2024-07-11T22:28:07Z

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.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
---
virt/kvm/guest_memfd.c | 47 ++++++++++++++++--------------------------
1 file changed, 18 insertions(+), 29 deletions(-)

diff --git a/virt/kvm/guest_memfd.c b/virt/kvm/guest_memfd.c
index f637327ad8e1..f4d82719ec19 100644
--- 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))
+ return 0;

- 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;
- }
+ 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;
}

@@ -63,7 +53,7 @@ static int __kvm_gmem_prepare_folio(struct inode *inode, pgoff_t index, struct f
* so that the guest can use it. 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;
@@ -92,8 +82,7 @@ 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);

@@ -616,7 +605,7 @@ 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);
--
2.43.0