KVM_ARM_VM_SMCCC_FILTER rejects an empty range (nr_functions == 0) with -EINVAL for every base except 0. kvm_smccc_set_filter() only rejects a range if its inclusive end, base + nr_functions - 1, is below base; for base 0 that end wraps to U32_MAX, and KVM then tries to insert [0, U32_MAX], which overlaps the reserved Arm Architecture Calls ranges, so the attribute returns -EEXIST instead of -EINVAL.
The request is rejected either way; only the errno is wrong, so this is a minor UAPI validation fix. Patch 1 rejects a zero function count explicitly. Patch 2 adds the base 0 case to test_invalid_nr_functions(), which only covered a nonzero base and therefore never caught this. Tested on an arm64 KVM host in VHE mode running under QEMU TCG: a small userspace reproducer gets EEXIST before patch 1 and EINVAL after it, and the smccc_filter selftest including the new assertion passes with patch 1 applied and fails at the new assertion with EEXIST without it. Karl Mehltretter (2): KVM: arm64: Return -EINVAL for an empty SMCCC filter range at base 0 KVM: arm64: selftests: Test empty SMCCC filter range at base 0 arch/arm64/kvm/hypercalls.c | 3 ++- tools/testing/selftests/kvm/arm64/smccc_filter.c | 4 ++++ 2 files changed, 6 insertions(+), 1 deletion(-) base-commit: 548e7bcd0c5460ddcbca9600cea603ebeebf4da7 -- 2.39.5 (Apple Git-154)
