[PATCH v12 20/84] KVM: Use NULL for struct page pointer to indicate mremapped memory

Sean Christopherson
2024-07-27T00:01:11Z

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.

Signed-off-by: Sean Christopherson <seanjc@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 f42e030f69a4..a5dcb72bab00 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 67a50b87bb87..3d717a131906 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -3088,7 +3088,7 @@ 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;

@@ -3114,7 +3114,7 @@ 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