Re: [PATCH 1/2] KVM: selftests: Fix MADV_COLLAPSE build failure on older toolchains

[Sean Christopherson <seanjc@google.com>]

On Mon, May 11, 2026, Fuad Tabba wrote:
> guest_memfd_test.c uses MADV_COLLAPSE unconditionally, but the
> constant was only exposed in glibc 2.37. Distros still on older glibc
> (e.g. Debian Bookworm, glibc 2.36) cannot build the test.
> 
> Add a compile-time fallback that defines MADV_COLLAPSE to its
> kernel-ABI value when the libc header does not, matching the
> established selftest pattern for sometimes-missing libc constants
> (see selftests/bpf/uprobe_multi.c, selftests/mm/hugetlb-soft-offline.c).
> 
> Fixes: 9830209b4ae8 ("KVM: selftests: Test MADV_COLLAPSE on guest_memfd")
> Signed-off-by: Fuad Tabba <tabba@google.com>
> ---
>  tools/testing/selftests/kvm/guest_memfd_test.c | 4 ++++
>  1 file changed, 4 insertions(+)
> 
> diff --git a/tools/testing/selftests/kvm/guest_memfd_test.c b/tools/testing/selftests/kvm/guest_memfd_test.c
> index d6528c6f5e03..45990ae5f1e5 100644
> --- a/tools/testing/selftests/kvm/guest_memfd_test.c
> +++ b/tools/testing/selftests/kvm/guest_memfd_test.c
> @@ -23,6 +23,10 @@
>  #include "test_util.h"
>  #include "ucall_common.h"
>  
> +#ifndef MADV_COLLAPSE
> +#define MADV_COLLAPSE	25
> +#endif

Fixed by:

  https://lore.kernel.org/all/20260428012503.1213654-1-seanjc@google.com

I'll get that applied and on its way to Paolo this week.