Re: [PATCH kvmtool 1/5] arm64: Do not abort on register-dump failures

[Suzuki K Poulose <suzuki.poulose@arm.com>]

On 31/08/2026 20:24, Fuad Tabba wrote:
> kvm_cpu__show_registers() and kvm_cpu__show_code() read the vCPU's core
> registers with KVM_GET_ONE_REG, and die() if the ioctl fails. Both are
> diagnostics. They run from the KVM_EXIT_DEBUG case in kvm_cpu__start(),
> from the "lkvm debug -d" dump path in handle_sigusr1(), and from the
> panic dump in kvm_cpu_thread().
> 
> Once a protected vCPU has run, its registers belong to the guest and
> KVM_GET_ONE_REG returns -EPERM. Dying on that turns a diagnostic into a
> VMM abort.

Marc once suggested that these could always succeed with junk values for
protected/Realm VMs. Do you think that is an option for pKVM ?


If we go with this approach :

Reviewed-by: Suzuki K Poulose <suzuki.poulose@arm.com>


> 
> Report that the register state is unavailable, with the errno, and
> return instead of dying.
> 
> Signed-off-by: Fuad Tabba <fuad.tabba@linux.dev>
> ---
>   arm64/kvm-cpu.c | 36 ++++++++++++++++++++++++------------
>   1 file changed, 24 insertions(+), 12 deletions(-)
> 
> diff --git a/arm64/kvm-cpu.c b/arm64/kvm-cpu.c
> index 3aa7684..c58d61f 100644
> --- a/arm64/kvm-cpu.c
> +++ b/arm64/kvm-cpu.c
> @@ -476,15 +476,19 @@ void kvm_cpu__show_code(struct kvm_cpu *vcpu)
>   
>   	dprintf(debug_fd, "\n*pc:\n");
>   	reg.id = ARM64_CORE_REG(regs.pc);
> -	if (ioctl(vcpu->vcpu_fd, KVM_GET_ONE_REG, &reg) < 0)
> -		die("KVM_GET_ONE_REG failed (show_code @ PC)");
> +	if (ioctl(vcpu->vcpu_fd, KVM_GET_ONE_REG, &reg) < 0) {
> +		pr_err("register state unavailable (pc): %s", strerror(errno));
> +		return;
> +	}

>   
>   	kvm__dump_mem(vcpu->kvm, data, 32, debug_fd);
>   
>   	dprintf(debug_fd, "\n*lr:\n");
>   	reg.id = ARM64_CORE_REG(regs.regs[30]);
> -	if (ioctl(vcpu->vcpu_fd, KVM_GET_ONE_REG, &reg) < 0)
> -		die("KVM_GET_ONE_REG failed (show_code @ LR)");
> +	if (ioctl(vcpu->vcpu_fd, KVM_GET_ONE_REG, &reg) < 0) {
> +		pr_err("register state unavailable (lr): %s", strerror(errno));
> +		return;
> +	}
>   
>   	kvm__dump_mem(vcpu->kvm, data, 32, debug_fd);
>   }
> @@ -499,23 +503,31 @@ void kvm_cpu__show_registers(struct kvm_cpu *vcpu)
>   	dprintf(debug_fd, "\n Registers:\n");
>   
>   	reg.id		= ARM64_CORE_REG(regs.pc);
> -	if (ioctl(vcpu->vcpu_fd, KVM_GET_ONE_REG, &reg) < 0)
> -		die("KVM_GET_ONE_REG failed (pc)");
> +	if (ioctl(vcpu->vcpu_fd, KVM_GET_ONE_REG, &reg) < 0) {
> +		pr_err("register state unavailable (pc): %s", strerror(errno));
> +		return;
> +	}
>   	dprintf(debug_fd, " PC:    0x%lx\n", data);
>   
>   	reg.id		= ARM64_CORE_REG(regs.pstate);
> -	if (ioctl(vcpu->vcpu_fd, KVM_GET_ONE_REG, &reg) < 0)
> -		die("KVM_GET_ONE_REG failed (pstate)");
> +	if (ioctl(vcpu->vcpu_fd, KVM_GET_ONE_REG, &reg) < 0) {
> +		pr_err("register state unavailable (pstate): %s", strerror(errno));
> +		return;
> +	}
>   	dprintf(debug_fd, " PSTATE:    0x%lx\n", data);
>   
>   	reg.id		= ARM64_CORE_REG(sp_el1);
> -	if (ioctl(vcpu->vcpu_fd, KVM_GET_ONE_REG, &reg) < 0)
> -		die("KVM_GET_ONE_REG failed (sp_el1)");
> +	if (ioctl(vcpu->vcpu_fd, KVM_GET_ONE_REG, &reg) < 0) {
> +		pr_err("register state unavailable (sp_el1): %s", strerror(errno));
> +		return;
> +	}
>   	dprintf(debug_fd, " SP_EL1:    0x%lx\n", data);
>   
>   	reg.id		= ARM64_CORE_REG(regs.regs[30]);
> -	if (ioctl(vcpu->vcpu_fd, KVM_GET_ONE_REG, &reg) < 0)
> -		die("KVM_GET_ONE_REG failed (lr)");
> +	if (ioctl(vcpu->vcpu_fd, KVM_GET_ONE_REG, &reg) < 0) {
> +		pr_err("register state unavailable (lr): %s", strerror(errno));
> +		return;
> +	}
>   	dprintf(debug_fd, " LR:    0x%lx\n", data);
>   }
>