linux-kernel - [RFC PATCH v2 06/51] KVM: Query guest

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Message-ID: <237590b163506821120734a0c8aad95d9c7ef299.1747264138.git.ackerleytng@google.com>
Date: Wed, 14 May 2025 16:41:45 -0700
From: Ackerley Tng <ackerleytng@...gle.com>
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Subject: [RFC PATCH v2 06/51] KVM: Query guest_memfd for private/shared status

Query guest_memfd for private/shared status if those guest_memfds
track private/shared status.

With this patch, Coco VMs can use guest_memfd for both shared and
private memory. If Coco VMs choose to use guest_memfd for both
shared and private memory, by creating guest_memfd with the
GUEST_MEMFD_FLAG_SUPPORT_SHARED flag, guest_memfd will be used to
provide the private/shared status of the memory, instead of
kvm->mem_attr_array.

Change-Id: I8f23d7995c12242aa4e09ccf5ec19360e9c9ed83
Signed-off-by: Ackerley Tng <ackerleytng@...gle.com>
---
 include/linux/kvm_host.h | 19 ++++++++++++-------
 virt/kvm/guest_memfd.c   | 22 ++++++++++++++++++++++
 2 files changed, 34 insertions(+), 7 deletions(-)

diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
index b317392453a5..91279e05e010 100644
--- a/include/linux/kvm_host.h
+++ b/include/linux/kvm_host.h
@@ -2508,12 +2508,22 @@ static inline void kvm_prepare_memory_fault_exit(struct kvm_vcpu *vcpu,
 }
 
 #ifdef CONFIG_KVM_GMEM_SHARED_MEM
+
 bool kvm_gmem_memslot_supports_shared(const struct kvm_memory_slot *slot);
+bool kvm_gmem_is_private(struct kvm_memory_slot *slot, gfn_t gfn);
+
 #else
+
 static inline bool kvm_gmem_memslot_supports_shared(const struct kvm_memory_slot *slot)
 {
 	return false;
 }
+
+static inline bool kvm_gmem_is_private(struct kvm_memory_slot *slot, gfn_t gfn)
+{
+	return false;
+}
+
 #endif /* CONFIG_KVM_GMEM_SHARED_MEM */
 
 #ifdef CONFIG_KVM_GENERIC_MEMORY_ATTRIBUTES
@@ -2544,13 +2554,8 @@ static inline bool kvm_mem_is_private(struct kvm *kvm, gfn_t gfn)
 		return false;
 
 	slot = gfn_to_memslot(kvm, gfn);
-	if (kvm_slot_has_gmem(slot) && kvm_gmem_memslot_supports_shared(slot)) {
-		/*
-		 * For now, memslots only support in-place shared memory if the
-		 * host is allowed to mmap memory (i.e., non-Coco VMs).
-		 */
-		return false;
-	}
+	if (kvm_slot_has_gmem(slot) && kvm_gmem_memslot_supports_shared(slot))
+		return kvm_gmem_is_private(slot, gfn);
 
 	return kvm_get_memory_attributes(kvm, gfn) & KVM_MEMORY_ATTRIBUTE_PRIVATE;
 }
diff --git a/virt/kvm/guest_memfd.c b/virt/kvm/guest_memfd.c
index 6f6c4d298f8f..853e989bdcb2 100644
--- a/virt/kvm/guest_memfd.c
+++ b/virt/kvm/guest_memfd.c
@@ -865,6 +865,28 @@ bool kvm_gmem_memslot_supports_shared(const struct kvm_memory_slot *slot)
 }
 EXPORT_SYMBOL_GPL(kvm_gmem_memslot_supports_shared);
 
+bool kvm_gmem_is_private(struct kvm_memory_slot *slot, gfn_t gfn)
+{
+	struct inode *inode;
+	struct file *file;
+	pgoff_t index;
+	bool ret;
+
+	file = kvm_gmem_get_file(slot);
+	if (!file)
+		return false;
+
+	index = kvm_gmem_get_index(slot, gfn);
+	inode = file_inode(file);
+
+	filemap_invalidate_lock_shared(inode->i_mapping);
+	ret = kvm_gmem_shareability_get(inode, index) == SHAREABILITY_GUEST;
+	filemap_invalidate_unlock_shared(inode->i_mapping);
+
+	fput(file);
+	return ret;
+}
+
 #else
 #define kvm_gmem_mmap NULL
 #endif /* CONFIG_KVM_GMEM_SHARED_MEM */
-- 
2.49.0.1045.g170613ef41-goog