On 28/04/2026 21:12, David Woodhouse wrote:
From: David Woodhouse <[email protected]>Commit 3617c0ee7decb ("KVM: x86/xen: Only write Xen hypercall page for guest writes to MSR") blocked host-initiated writes from triggering the Xen hypercall page setup, to fix an SRCU usage violation when the hypercall MSR index collides with a real MSR written during vCPU reset. However, some VMMs legitimately need to trigger hypercall page setup from host context. For example, a VMM may intercept the guest's MSR write to track an epoch (for kexec/crash recovery), and then replay the write as a host-initiated KVM_SET_MSRS to populate the hypercall page. The host_initiated check breaks this use case. Add KVM_XEN_VCPU_ATTR_TYPE_WRITE_HYPERCALL_PAGE as a new vcpu attribute that explicitly invokes kvm_xen_write_hypercall_page() under proper locking. This gives userspace a safe interface to trigger hypercall page setup without going through the MSR write path, preserving the host_initiated defence in depth while restoring the lost functionality. Fixes: 3617c0ee7dec ("KVM: x86/xen: Only write Xen hypercall page for guest writes to MSR") Signed-off-by: David Woodhouse <[email protected]> --- Documentation/virt/kvm/api.rst | 11 +++ arch/x86/include/uapi/asm/kvm.h | 3 + arch/x86/kvm/x86.c | 3 +- arch/x86/kvm/xen.c | 7 ++ .../selftests/kvm/x86/xen_vmcall_test.c | 96 +++++++++++++++++++ 5 files changed, 119 insertions(+), 1 deletion(-)
Reviewed-by: Paul Durrant <[email protected]>
