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KVM: guest_memfd: Add interface for populating gmem pages with user data

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During guest run-time, kvm_arch_gmem_prepare() is issued as needed to
prepare newly-allocated gmem pages prior to mapping them into the guest.
In the case of SEV-SNP, this mainly involves setting the pages to
private in the RMP table.

However, for the GPA ranges comprising the initial guest payload, which
are encrypted/measured prior to starting the guest, the gmem pages need
to be accessed prior to setting them to private in the RMP table so they
can be initialized with the userspace-provided data. Additionally, an
SNP firmware call is needed afterward to encrypt them in-place and
measure the contents into the guest's launch digest.

While it is possible to bypass the kvm_arch_gmem_prepare() hooks so that
this handling can be done in an open-coded/vendor-specific manner, this
may expose more gmem-internal state/dependencies to external callers
than necessary. Try to avoid this by implementing an interface that
tries to handle as much of the common functionality inside gmem as
possible, while also making it generic enough to potentially be
usable/extensible for TDX as well.

Suggested-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: Michael Roth <michael.roth@amd.com>
Co-developed-by: Michael Roth <michael.roth@amd.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
This commit is contained in:
Paolo Bonzini
2024-02-14 12:09:06 -05:00
parent 17573fd971
commit 1f6c06b177
2 changed files with 79 additions and 0 deletions
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52
virt/kvm/guest_memfd.c
View File

@@ -585,3 +585,55 @@ int kvm_gmem_get_pfn(struct kvm *kvm, struct kvm_memory_slot *slot,
return r;
}
EXPORT_SYMBOL_GPL(kvm_gmem_get_pfn);
long kvm_gmem_populate(struct kvm *kvm, gfn_t start_gfn, void __user *src, long npages,
kvm_gmem_populate_cb post_populate, void *opaque)
{
struct file *file;
struct kvm_memory_slot *slot;
void __user *p;
int ret = 0, max_order;
long i;
lockdep_assert_held(&kvm->slots_lock);
if (npages < 0)
return -EINVAL;
slot = gfn_to_memslot(kvm, start_gfn);
if (!kvm_slot_can_be_private(slot))
return -EINVAL;
file = kvm_gmem_get_file(slot);
if (!file)
return -EFAULT;
filemap_invalidate_lock(file->f_mapping);
npages = min_t(ulong, slot->npages - (start_gfn - slot->base_gfn), npages);
for (i = 0; i < npages; i += (1 << max_order)) {
gfn_t gfn = start_gfn + i;
kvm_pfn_t pfn;
ret = __kvm_gmem_get_pfn(file, slot, gfn, &pfn, &max_order, false);
if (ret)
break;
if (!IS_ALIGNED(gfn, (1 << max_order)) ||
(npages - i) < (1 << max_order))
max_order = 0;
p = src ? src + i * PAGE_SIZE : NULL;
ret = post_populate(kvm, gfn, pfn, p, max_order, opaque);
put_page(pfn_to_page(pfn));
if (ret)
break;
}
filemap_invalidate_unlock(file->f_mapping);
fput(file);
return ret && !i ? ret : i;
}
EXPORT_SYMBOL_GPL(kvm_gmem_populate);