linux-kernel - [RFC PATCH 28/39] KVM: guest_memfd: Use vm_type to determine default faultability

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Message-ID: <bf66353ee3338f11283a3f4b7ed1f06bd0b268a6.1726009989.git.ackerleytng@google.com>
Date: Tue, 10 Sep 2024 23:43:59 +0000
From: Ackerley Tng <ackerleytng@...gle.com>
To: tabba@...gle.com, quic_eberman@...cinc.com, roypat@...zon.co.uk, 
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Subject: [RFC PATCH 28/39] KVM: guest_memfd: Use vm_type to determine default faultability

Memory of a KVM_X86_SW_PROTECTED_VM defaults to faultable to align
with the default in kvm->mem_attr_array.

For this RFC, determine default faultability when associating a range
with a memslot.

Another option is to determine default faultability at guest_memfd
creation time. guest_memfd is created for a specific VM, hence we can
set default faultability based on the VM type.

In future, if different struct kvms are bound to the same guest_memfd
inode, all the struct kvms must be of the same vm_type.

TODO: Perhaps faultability should be based on kvm->mem_attr_array?

Signed-off-by: Ackerley Tng <ackerleytng@...gle.com>

---
 virt/kvm/guest_memfd.c | 22 ++++++++++++++++++++++
 1 file changed, 22 insertions(+)

diff --git a/virt/kvm/guest_memfd.c b/virt/kvm/guest_memfd.c
index fc2483e35876..1d4dfe0660ad 100644
--- a/virt/kvm/guest_memfd.c
+++ b/virt/kvm/guest_memfd.c
@@ -1256,6 +1256,23 @@ static struct file *kvm_gmem_inode_create_getfile(void *priv, loff_t size,
 	return file;
 }
 
+static void kvm_gmem_set_default_faultability_by_vm_type(struct inode *inode,
+							 u8 vm_type,
+							 loff_t start, loff_t end)
+{
+	bool faultable;
+
+	switch (vm_type) {
+	case KVM_X86_SW_PROTECTED_VM:
+		faultable = true;
+		break;
+	default:
+		faultable = false;
+	}
+
+	WARN_ON(kvm_gmem_set_faultable(inode, start, end, faultable));
+}
+
 static int __kvm_gmem_create(struct kvm *kvm, loff_t size, u64 flags)
 {
 	struct kvm_gmem *gmem;
@@ -1378,6 +1395,11 @@ int kvm_gmem_bind(struct kvm *kvm, struct kvm_memory_slot *slot,
 	slot->gmem.pgoff = start;
 
 	xa_store_range(&gmem->bindings, start, end - 1, slot, GFP_KERNEL);
+
+	kvm_gmem_set_default_faultability_by_vm_type(file_inode(file),
+						     kvm->arch.vm_type,
+						     start, end);
+
 	filemap_invalidate_unlock(inode->i_mapping);
 
 	/*
-- 
2.46.0.598.g6f2099f65c-goog