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

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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>
This commit is contained in:
Paolo Bonzini 2024-07-11 18:27:50 -04:00
parent b85524314a
commit 6dd761d92f
1 changed files with 18 additions and 29 deletions
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47
virt/kvm/guest_memfd.c
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@ -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)); 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 #ifdef CONFIG_HAVE_KVM_ARCH_GMEM_PREPARE
struct list_head *gmem_list = &inode->i_mapping->i_private_list; kvm_pfn_t pfn;
struct kvm_gmem *gmem; gfn_t gfn;
int rc;
list_for_each_entry(gmem, gmem_list, entry) { if (!kvm_arch_gmem_prepare_needed(kvm))
struct kvm_memory_slot *slot; return 0;
struct kvm *kvm = gmem->kvm;
kvm_pfn_t pfn;
gfn_t gfn;
int rc;
if (!kvm_arch_gmem_prepare_needed(kvm)) pfn = folio_file_pfn(folio, index);
continue; gfn = slot->base_gfn + index - slot->gmem.pgoff;
rc = kvm_arch_gmem_prepare(kvm, gfn, pfn, folio_order(folio));
slot = xa_load(&gmem->bindings, index); if (rc) {
if (!slot) pr_warn_ratelimited("gmem: Failed to prepare folio for index %lx GFN %llx PFN %llx error %d.\n",
continue; index, 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 GFN %llx PFN %llx error %d.\n",
gfn, pfn, rc);
return rc;
}
} }
#endif #endif
return 0; 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 * On successful return the guest sees a zero page so as to avoid
* leaking host data and the up-to-date flag is set. * 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) gfn_t gfn, struct folio *folio)
{ {
unsigned long nr_pages, i; 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))); WARN_ON(!IS_ALIGNED(slot->gmem.pgoff, 1 << folio_order(folio)));
index = gfn - slot->base_gfn + slot->gmem.pgoff; index = gfn - slot->base_gfn + slot->gmem.pgoff;
index = ALIGN_DOWN(index, 1 << folio_order(folio)); index = ALIGN_DOWN(index, 1 << folio_order(folio));
r = __kvm_gmem_prepare_folio(kvm, slot, index, folio);
r = __kvm_gmem_prepare_folio(file_inode(file), index, folio);
if (!r) if (!r)
folio_mark_uptodate(folio); folio_mark_uptodate(folio);
@ -619,7 +608,7 @@ int kvm_gmem_get_pfn(struct kvm *kvm, struct kvm_memory_slot *slot,
goto out; goto out;
} }
r = kvm_gmem_prepare_folio(file, slot, gfn, folio); r = kvm_gmem_prepare_folio(kvm, slot, gfn, folio);
folio_unlock(folio); folio_unlock(folio);
if (r < 0) if (r < 0)
folio_put(folio); folio_put(folio);