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KVM: guest_memfd: delay folio_mark_uptodate() until after successful preparation

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The up-to-date flag as is now is not too useful; it tells guest_memfd not
to overwrite the contents of a folio, but it doesn't say that the page
is ready to be mapped into the guest.  For encrypted guests, mapping
a private page requires that the "preparation" phase has succeeded,
and at the same time the same page cannot be prepared twice.

So, ensure that folio_mark_uptodate() is only called on a prepared page.  If
kvm_gmem_prepare_folio() or the post_populate callback fail, the folio
will not be marked up-to-date; it's not a problem to call clear_highpage()
again on such a page prior to the next preparation attempt.

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 18:27:45 -04:00
parent d0d87226f5
commit d04c77d231
1 changed files with 4 additions and 2 deletions
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6
virt/kvm/guest_memfd.c
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@ -73,8 +73,6 @@ static struct folio *kvm_gmem_get_folio(struct inode *inode, pgoff_t index, bool
for (i = 0; i < nr_pages; i++)
clear_highpage(folio_page(folio, i));
folio_mark_uptodate(folio);
}
if (prepare) {
@ -84,6 +82,8 @@ static struct folio *kvm_gmem_get_folio(struct inode *inode, pgoff_t index, bool
folio_put(folio);
return ERR_PTR(r);
}
folio_mark_uptodate(folio);
}
/*
@ -646,6 +646,8 @@ long kvm_gmem_populate(struct kvm *kvm, gfn_t start_gfn, void __user *src, long
p = src ? src + i * PAGE_SIZE : NULL;
ret = post_populate(kvm, gfn, pfn, p, max_order, opaque);
if (!ret)
folio_mark_uptodate(folio);
folio_put(folio);
if (ret)