Re: [PATCH v8 25/46] KVM: guest_memfd: Enable INIT_SHARED on guest_memfd for x86 Coco VMs
From: Xiaoyao Li <hidden>
Date: 2026-07-01 11:18:51
Also in:
kvm, linux-coco, linux-doc, linux-kselftest, linux-mm, lkml
On 6/19/2026 8:32 AM, Ackerley Tng via B4 Relay wrote:
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 in-place conversion is enabled, i.e. when it's actually possible for a guest_memfd instance to contain shared memory. Signed-off-by: Sean Christopherson <seanjc@google.com> Reviewed-by: Fuad Tabba <redacted> Signed-off-by: Ackerley Tng <redacted>
Reviewed-by: Xiaoyao Li <redacted>
quoted hunk ↗ jump to hunk
--- arch/x86/kvm/x86.c | 13 +++++++------ 1 file changed, 7 insertions(+), 6 deletions(-)diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c index 2fde594e86d72..57a543dadb851 100644 --- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c@@ -14116,14 +14116,15 @@ 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 is supported if in-place conversion is enabled, or if + * the VM doesn't support private memory. If the VM has private memory + * and in-place conversion is disabled, then guest_memfd can _only_ be + * used for private memory. + */ + return gmem_in_place_conversion || !kvm_arch_has_private_mem(kvm); } #ifdef CONFIG_HAVE_KVM_ARCH_GMEM_PREPARE