KVM: MMU: add KVM_ZAP_GFN ioctl

[Marcelo Tosatti <marcelo@kvack.org>]

Add an ioctl to zap all mappings to a given gfn. This allows userspace
remove the QEMU process mappings and the page without causing
inconsistency.

Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>


diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c
index f0cdfba..c41464f 100644
--- a/arch/x86/kvm/mmu.c
+++ b/arch/x86/kvm/mmu.c
@@ -642,6 +642,67 @@ static void rmap_write_protect(struct kvm *kvm, u64 gfn)
 	account_shadowed(kvm, gfn);
 }
 
+static void rmap_nuke(struct kvm *kvm, u64 gfn)
+{
+	unsigned long *rmapp;
+	u64 *spte;
+	int nuked = 0;
+
+	gfn = unalias_gfn(kvm, gfn);
+	rmapp = gfn_to_rmap(kvm, gfn, 0);
+
+	spte = rmap_next(kvm, rmapp, NULL);
+	while (spte) {
+		BUG_ON(!spte);
+		BUG_ON(!(*spte & PT_PRESENT_MASK));
+		rmap_printk("rmap_nuke: spte %p %llx\n", spte, *spte);
+		rmap_remove(kvm, spte);
+		set_shadow_pte(spte, shadow_trap_nonpresent_pte);
+                nuked = 1;
+		spte = rmap_next(kvm, rmapp, spte);
+	}
+	/* check for huge page mappings */
+	rmapp = gfn_to_rmap(kvm, gfn, 1);
+	spte = rmap_next(kvm, rmapp, NULL);
+	while (spte) {
+		BUG_ON(!spte);
+		BUG_ON(!(*spte & PT_PRESENT_MASK));
+		BUG_ON((*spte & (PT_PAGE_SIZE_MASK|PT_PRESENT_MASK)) != (PT_PAGE_SIZE_MASK|PT_PRESENT_MASK));
+		pgprintk("rmap_nuke(large): spte %p %llx %lld\n", spte, *spte, gfn);
+		rmap_remove(kvm, spte);
+		--kvm->stat.lpages;
+		set_shadow_pte(spte, shadow_trap_nonpresent_pte);
+		nuked = 1;
+		spte = rmap_next(kvm, rmapp, spte);
+	}
+
+	if (nuked)
+		kvm_flush_remote_tlbs(kvm);
+}
+
+int kvm_zap_single_gfn(struct kvm *kvm, gfn_t gfn)
+{
+	unsigned long addr;
+	int have_mmu_notifiers = 0;
+
+	down_read(&kvm->slots_lock);
+	addr = gfn_to_hva(kvm, gfn);
+
+	if (kvm_is_error_hva(addr)) {
+		up_read(&kvm->slots_lock);
+		return -EINVAL;
+	}
+
+	if (!have_mmu_notifiers) {
+		spin_lock(&kvm->mmu_lock);
+		rmap_nuke(kvm, gfn);
+		spin_unlock(&kvm->mmu_lock);
+	}
+	up_read(&kvm->slots_lock);
+
+	return 0;
+}
+
 #ifdef MMU_DEBUG
 static int is_empty_shadow_page(u64 *spt)
 {
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index e65a9d6..d982ca1 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -816,6 +816,9 @@ int kvm_dev_ioctl_check_extension(long ext)
 	case KVM_CAP_NR_MEMSLOTS:
 		r = KVM_MEMORY_SLOTS;
 		break;
+	case KVM_CAP_ZAP_GFN:
+		r = 1;
+		break;
 	default:
 		r = 0;
 		break;
@@ -1636,6 +1639,15 @@ long kvm_arch_vm_ioctl(struct file *filp,
 		r = 0;
 		break;
 	}
+	case KVM_ZAP_GFN: {
+		gfn_t gfn;
+
+		r = -EFAULT;
+		if (copy_from_user(&gfn, argp, sizeof gfn))
+			goto out;
+		r = kvm_zap_single_gfn(kvm, gfn);
+		break;
+        } 
 	default:
 		;
 	}
diff --git a/include/asm-x86/kvm_host.h b/include/asm-x86/kvm_host.h
index 024b57c..4e45bd2 100644
--- a/include/asm-x86/kvm_host.h
+++ b/include/asm-x86/kvm_host.h
@@ -425,6 +425,7 @@ void kvm_mmu_set_nonpresent_ptes(u64 trap_pte, u64 notrap_pte);
 int kvm_mmu_reset_context(struct kvm_vcpu *vcpu);
 void kvm_mmu_slot_remove_write_access(struct kvm *kvm, int slot);
 void kvm_mmu_zap_all(struct kvm *kvm);
+int  kvm_zap_single_gfn(struct kvm *kvm, gfn_t gfn);
 unsigned int kvm_mmu_calculate_mmu_pages(struct kvm *kvm);
 void kvm_mmu_change_mmu_pages(struct kvm *kvm, unsigned int kvm_nr_mmu_pages);
 
diff --git a/include/linux/kvm.h b/include/linux/kvm.h
index e92e703..9ea714f 100644
--- a/include/linux/kvm.h
+++ b/include/linux/kvm.h
@@ -236,6 +236,7 @@ struct kvm_vapic_addr {
 #define KVM_CAP_CLOCKSOURCE 8
 #define KVM_CAP_NR_VCPUS 9       /* returns max vcpus per vm */
 #define KVM_CAP_NR_MEMSLOTS 10   /* returns max memory slots per vm */
+#define KVM_CAP_ZAP_GFN	11
 
 /*
  * ioctls for VM fds
@@ -258,6 +259,7 @@ struct kvm_vapic_addr {
 #define KVM_IRQ_LINE		  _IOW(KVMIO, 0x61, struct kvm_irq_level)
 #define KVM_GET_IRQCHIP		  _IOWR(KVMIO, 0x62, struct kvm_irqchip)
 #define KVM_SET_IRQCHIP		  _IOR(KVMIO,  0x63, struct kvm_irqchip)
+#define KVM_ZAP_GFN	   	  _IOR(KVMIO,  0x64, unsigned long)
 
 /*
  * ioctls for vcpu fds

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