[PATCH v13 22/85] KVM: Use NULL for struct page pointer to indicate mremapped memory

[Sean Christopherson]

Drop yet another unnecessary magic page value from KVM, as there's zero
reason to use a poisoned pointer to indicate "no page".  If KVM uses a
NULL page pointer, the kernel will explode just as quickly as if KVM uses
a poisoned pointer.  Never mind the fact that such usage would be a
blatant and egregious KVM bug.

Tested-by: Alex Bennée <alex.bennee at linaro.org>
Signed-off-by: Sean Christopherson <seanjc at google.com>
---
 include/linux/kvm_host.h | 4 ----
 virt/kvm/kvm_main.c      | 4 ++--
 2 files changed, 2 insertions(+), 6 deletions(-)

diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
index cbc7b9c04c14..e3c01cbbc41a 100644
--- a/include/linux/kvm_host.h
+++ b/include/linux/kvm_host.h
@@ -273,16 +273,12 @@ enum {
 	READING_SHADOW_PAGE_TABLES,
 };
 
-#define KVM_UNMAPPED_PAGE	((void *) 0x500 + POISON_POINTER_DELTA)
-
 struct kvm_host_map {
 	/*
 	 * Only valid if the 'pfn' is managed by the host kernel (i.e. There is
 	 * a 'struct page' for it. When using mem= kernel parameter some memory
 	 * can be used as guest memory but they are not managed by host
 	 * kernel).
-	 * If 'pfn' is not managed by the host kernel, this field is
-	 * initialized to KVM_UNMAPPED_PAGE.
 	 */
 	struct page *page;
 	void *hva;
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index f1c9a781315c..7acb1a8af2e4 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -3067,7 +3067,7 @@ void kvm_release_pfn(kvm_pfn_t pfn, bool dirty)
 
 int kvm_vcpu_map(struct kvm_vcpu *vcpu, gfn_t gfn, struct kvm_host_map *map)
 {
-	map->page = KVM_UNMAPPED_PAGE;
+	map->page = NULL;
 	map->hva = NULL;
 	map->gfn = gfn;
 
@@ -3093,7 +3093,7 @@ void kvm_vcpu_unmap(struct kvm_vcpu *vcpu, struct kvm_host_map *map, bool dirty)
 	if (!map->hva)
 		return;
 
-	if (map->page != KVM_UNMAPPED_PAGE)
+	if (map->page)
 		kunmap(map->page);
 #ifdef CONFIG_HAS_IOMEM
 	else
-- 
2.47.0.rc1.288.g06298d1525-goog