KVM: Use NULL for struct page pointer to indicate mremapped memory

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@linaro.org>
Signed-off-by: Sean Christopherson <seanjc@google.com>
Tested-by: Dmitry Osipenko <dmitry.osipenko@collabora.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Message-ID: <20241010182427.1434605-23-seanjc@google.com>

diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
index 2c9eb472f05959921ad477041fc5f4ca7a27fd56..cd6f5cc1930f5f3ebb4a3c660adc2360f96a9c7d 100644 (file)
--- 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 4074f49eb3f17928aa793a111a8375313c0ef6ae..c20386a8aa3eaf1e656b9f874041cd2a9012def2 100644 (file)
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -3061,7 +3061,7 @@ 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;
 
@@ -3087,7 +3087,7 @@ 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