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

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Message-ID: <20240726235234.228822-21-seanjc@google.com>
Date: Fri, 26 Jul 2024 16:51:29 -0700
From: Sean Christopherson <seanjc@...gle.com>
To: Paolo Bonzini <pbonzini@...hat.com>, Marc Zyngier <maz@...nel.org>, 
	Oliver Upton <oliver.upton@...ux.dev>, Tianrui Zhao <zhaotianrui@...ngson.cn>, 
	Bibo Mao <maobibo@...ngson.cn>, Huacai Chen <chenhuacai@...nel.org>, 
	Michael Ellerman <mpe@...erman.id.au>, Anup Patel <anup@...infault.org>, 
	Paul Walmsley <paul.walmsley@...ive.com>, Palmer Dabbelt <palmer@...belt.com>, 
	Albert Ou <aou@...s.berkeley.edu>, Christian Borntraeger <borntraeger@...ux.ibm.com>, 
	Janosch Frank <frankja@...ux.ibm.com>, Claudio Imbrenda <imbrenda@...ux.ibm.com>, 
	Sean Christopherson <seanjc@...gle.com>
Cc: kvm@...r.kernel.org, linux-arm-kernel@...ts.infradead.org, 
	kvmarm@...ts.linux.dev, loongarch@...ts.linux.dev, linux-mips@...r.kernel.org, 
	linuxppc-dev@...ts.ozlabs.org, kvm-riscv@...ts.infradead.org, 
	linux-riscv@...ts.infradead.org, linux-kernel@...r.kernel.org, 
	David Matlack <dmatlack@...gle.com>, David Stevens <stevensd@...omium.org>
Subject: [PATCH v12 20/84] 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.

Signed-off-by: Sean Christopherson <seanjc@...gle.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
-- 
2.46.0.rc1.232.g9752f9e123-goog