[Xen-devel] [PATCH RFC v1 08/12] powerpc/book3s: Prepare kvmppc_book3s_instantiate_page() for PG_reserved changes

[David Hildenbrand <david@xxxxxxxxxx>]

Right now, ZONE_DEVICE memory is always set PG_reserved. We want to
change that.

KVM has this weird use case that you can map anything from /dev/mem
into the guest. pfn_valid() is not a reliable check whether the memmap
was initialized and can be touched. pfn_to_online_page() makes sure
that we have an initialized memmap. Note that ZONE_DEVICE memory is
never online (IOW, managed by the buddy).

Switching to pfn_to_online_page() keeps the existing behavior for
PFNs without a memmap and for ZONE_DEVICE memory.

Cc: Paul Mackerras <paulus@xxxxxxxxxx>
Cc: Benjamin Herrenschmidt <benh@xxxxxxxxxxxxxxxxxxx>
Cc: Michael Ellerman <mpe@xxxxxxxxxxxxxx>
Signed-off-by: David Hildenbrand <david@xxxxxxxxxx>
---
 arch/powerpc/kvm/book3s_64_mmu_radix.c | 14 ++++++++------
 1 file changed, 8 insertions(+), 6 deletions(-)

diff --git a/arch/powerpc/kvm/book3s_64_mmu_radix.c 
b/arch/powerpc/kvm/book3s_64_mmu_radix.c
index 2d415c36a61d..05397c0561fc 100644
--- a/arch/powerpc/kvm/book3s_64_mmu_radix.c
+++ b/arch/powerpc/kvm/book3s_64_mmu_radix.c
@@ -801,12 +801,14 @@ int kvmppc_book3s_instantiate_page(struct kvm_vcpu *vcpu,
                                           writing, upgrade_p);
                if (is_error_noslot_pfn(pfn))
                        return -EFAULT;
-               page = NULL;
-               if (pfn_valid(pfn)) {
-                       page = pfn_to_page(pfn);
-                       if (PageReserved(page))
-                               page = NULL;
-               }
+               /*
+                * We treat any pages that are not online (not managed by the
+                * buddy) as reserved - this includes ZONE_DEVICE pages and
+                * pages without a memmap (e.g., mapped via /dev/mem).
+                */
+               page = pfn_to_online_page(pfn);
+               if (page && PageReserved(page))
+                       page = NULL;
        }
 
        /*
-- 
2.21.0


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