[PATCH RFC v4 09/44] KVM: guest_memfd: Enable INIT_SHARED on guest_memfd for x86 Coco VMs

Ackerley Tng
2026-03-26T22:24:51Z

From: Sean Christopherson <seanjc@google.com>

Now that guest_memfd supports tracking private vs. shared within gmem
itself, allow userspace to specify INIT_SHARED on a guest_memfd instance
for x86 Confidential Computing (CoCo) VMs, so long as per-VM attributes
are disabled, i.e. when it's actually possible for a guest_memfd instance
to contain shared memory.

Signed-off-by: Sean Christopherson <seanjc@google.com>
---
arch/x86/kvm/x86.c | 11 +++++------
1 file changed, 5 insertions(+), 6 deletions(-)

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 7e133a9da11f0..9c29407712580 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -14056,14 +14056,13 @@ bool kvm_arch_no_poll(struct kvm_vcpu *vcpu)
}

#ifdef CONFIG_KVM_GUEST_MEMFD
-/*
- * KVM doesn't yet support initializing guest_memfd memory as shared for VMs
- * with private memory (the private vs. shared tracking needs to be moved into
- * guest_memfd).
- */
bool kvm_arch_supports_gmem_init_shared(struct kvm *kvm)
{
- return !kvm_arch_has_private_mem(kvm);
+ /*
+ * INIT_SHARED isn't supported if the memory attributes are per-VM,
+ * in which case guest_memfd can _only_ be used for private memory.
+ */
+ return !vm_memory_attributes || !kvm_arch_has_private_mem(kvm);
}

#ifdef CONFIG_HAVE_KVM_ARCH_GMEM_PREPARE

--
2.53.0.1018.g2bb0e51243-goog