On Wed, 29 Apr 2026 12:36:52 +0200, Paul Durrant wrote: > 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]>
Ping?
smime.p7s
Description: S/MIME cryptographic signature
