Subject: [PATCH v1 03/10] KVM: Prepare kvm_is_reserved_pfn() for PG_reserved changes

From: David Hildenbrand <[email-masked]>
Date: Thu, 24 Oct 2019 14:09:31 +0200

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 (and don't have ZONE_DEVICE memory).

Rewrite kvm_is_reserved_pfn() to make sure the function produces the
same result once we stop setting ZONE_DEVICE pages PG_reserved.

Cc: Paolo Bonzini <[email-masked]>
Cc: "Radim Krčmář" <[email-masked]>
Cc: Michal Hocko <[email-masked]>
Cc: Dan Williams <[email-masked]>
Cc: KarimAllah Ahmed <[email-masked]>
Signed-off-by: David Hildenbrand <[email-masked]>
---
 virt/kvm/kvm_main.c | 10 ++++++++--
 1 file changed, 8 insertions(+), 2 deletions(-)

diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index e9eb666eb6e8..9d18cc67d124 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -151,9 +151,15 @@ __weak int kvm_arch_mmu_notifier_invalidate_range(struct kvm *kvm,
 
 bool kvm_is_reserved_pfn(kvm_pfn_t pfn)
 {
-	if (pfn_valid(pfn))
-		return PageReserved(pfn_to_page(pfn));
+	struct page *page = pfn_to_online_page(pfn);
 
+	/*
+	 * 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).
+	 */
+	if (page)
+		return PageReserved(page);
 	return true;
 }
 
-- 
2.21.0