Running a KVM guest using a 6.9-rc3 kernel, in a 6.8 host that has zkr enabled, will fail with a kernel oops SIGILL right at the start. The reason is that we can't expose zkr without implementing the SEED CSR. Disabling zkr in the guest would be a workaround, but if the KVM doesn't allow it we'll error out and never boot.
In hindsight this is too strict. If we keep proceeding, despite not disabling the extension in the KVM vcpu, we'll not add extension in riscv,isa. The guest kernel will be unaware of the extension, i.e. it doesn't matter if the KVM vcpu has it enabled underneath or not. So it's ok to keep booting in this case. Change our current logic to not error out if we fail to disable an extension in kvm_set_one_reg(): throw an warning instead and keep booting. We'll keep the existing behavior when we fail to enable an extension in KVM, since adding the extension in riscv,isa at this point will cause a guest malfunction because the extension isn't enabled in the vcpu. Suggested-by: Andrew Jones <ajo...@ventanamicro.com> Signed-off-by: Daniel Henrique Barboza <dbarb...@ventanamicro.com> --- target/riscv/kvm/kvm-cpu.c | 12 ++++++++---- 1 file changed, 8 insertions(+), 4 deletions(-) diff --git a/target/riscv/kvm/kvm-cpu.c b/target/riscv/kvm/kvm-cpu.c index 6a6c6cae80..261ca24504 100644 --- a/target/riscv/kvm/kvm-cpu.c +++ b/target/riscv/kvm/kvm-cpu.c @@ -427,10 +427,14 @@ static void kvm_riscv_update_cpu_cfg_isa_ext(RISCVCPU *cpu, CPUState *cs) reg = kvm_cpu_cfg_get(cpu, multi_ext_cfg); ret = kvm_set_one_reg(cs, id, ®); if (ret != 0) { - error_report("Unable to %s extension %s in KVM, error %d", - reg ? "enable" : "disable", - multi_ext_cfg->name, ret); - exit(EXIT_FAILURE); + if (reg) { + error_report("Unable to enable extension %s in KVM, error %d", + multi_ext_cfg->name, ret); + exit(EXIT_FAILURE); + } else { + warn_report("KVM did not disable extension %s (error %d)", + multi_ext_cfg->name, ret); + } } } } -- 2.44.0