KVM: arm64: Use common code's approach for __GFP_ZERO with memory caches

Add a "gfp_zero" member to arm64's 'struct kvm_mmu_memory_cache' to make
the struct and its usage compatible with the common 'struct
kvm_mmu_memory_cache' in linux/kvm_host.h.  This will minimize code
churn when arm64 moves to the common implementation in a future patch, at
the cost of temporarily having somewhat silly code.

Note, GFP_PGTABLE_USER is equivalent to GFP_KERNEL_ACCOUNT | GFP_ZERO:

  #define GFP_PGTABLE_USER  (GFP_PGTABLE_KERNEL | __GFP_ACCOUNT)
  |
  -> #define GFP_PGTABLE_KERNEL        (GFP_KERNEL | __GFP_ZERO)

  == GFP_KERNEL | __GFP_ACCOUNT | __GFP_ZERO

versus

  #define GFP_KERNEL_ACCOUNT (GFP_KERNEL | __GFP_ACCOUNT)

    with __GFP_ZERO explicitly OR'd in

  == GFP_KERNEL | __GFP_ACCOUNT | __GFP_ZERO

No functional change intended.
Tested-by: Marc Zyngier <maz@kernel.org>
Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
Message-Id: <20200703023545.8771-18-sean.j.christopherson@intel.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

arch/arm64/include/asm/kvm_host.h

@@ -105,6 +105,7 @@ struct kvm_arch {
  */
 struct kvm_mmu_memory_cache {
 	int nobjs;
+	gfp_t gfp_zero;
 	void *objects[KVM_NR_MEM_OBJS];
 };
 

arch/arm64/kvm/arm.c

@@ -270,6 +270,8 @@ int kvm_arch_vcpu_create(struct kvm_vcpu *vcpu)
 	vcpu->arch.target = -1;
 	bitmap_zero(vcpu->arch.features, KVM_VCPU_MAX_FEATURES);
 
+	vcpu->arch.mmu_page_cache.gfp_zero = __GFP_ZERO;
+
 	/* Set up the timer */
 	kvm_timer_vcpu_init(vcpu);
 

arch/arm64/kvm/mmu.c

@@ -131,7 +131,8 @@ static int mmu_topup_memory_cache(struct kvm_mmu_memory_cache *cache, int min)
 	if (cache->nobjs >= min)
 		return 0;
 	while (cache->nobjs < ARRAY_SIZE(cache->objects)) {
-		page = (void *)__get_free_page(GFP_PGTABLE_USER);
+		page = (void *)__get_free_page(GFP_KERNEL_ACCOUNT |
+					       cache->gfp_zero);
 		if (!page)
 			return -ENOMEM;
 		cache->objects[cache->nobjs++] = page;
@@ -1467,7 +1468,7 @@ int kvm_phys_addr_ioremap(struct kvm *kvm, phys_addr_t guest_ipa,
 	phys_addr_t addr, end;
 	int ret = 0;
 	unsigned long pfn;
-	struct kvm_mmu_memory_cache cache = { 0, };
+	struct kvm_mmu_memory_cache cache = { 0, __GFP_ZERO, };
 
 	end = (guest_ipa + size + PAGE_SIZE - 1) & PAGE_MASK;
 	pfn = __phys_to_pfn(pa);