Re: [PATCH kvmtool 2/2] cpu: vmexit: Handle KVM_EXIT_MEMORY_FAULT correctly

[Aneesh Kumar K.V <aneesh.kumar@kernel.org>]

Will Deacon <will@kernel.org> writes:

> On Tue, Feb 11, 2025 at 01:08:52PM +0530, Aneesh Kumar K.V (Arm) wrote:
>> Linux kernel documentation states:
>>
>> "Note! KVM_EXIT_MEMORY_FAULT is unique among all KVM exit reasons in
>> that it accompanies a return code of '-1', not '0'! errno will always be
>> set to EFAULT or EHWPOISON when KVM exits with KVM_EXIT_MEMORY_FAULT,
>> userspace should assume kvm_run.exit_reason is stale/undefined for all
>> other error numbers." "
>>
>> Update the KVM_RUN ioctl error handling to correctly handle
>> KVM_EXIT_MEMORY_FAULT.
>>
>> Signed-off-by: Aneesh Kumar K.V (Arm) <aneesh.kumar@kernel.org>
>> ---
>>  kvm-cpu.c | 11 +++++++++--
>>  1 file changed, 9 insertions(+), 2 deletions(-)
>>
>> diff --git a/kvm-cpu.c b/kvm-cpu.c
>> index 66e30ba54e26..40e4efc33a1d 100644
>> --- a/kvm-cpu.c
>> +++ b/kvm-cpu.c
>> @@ -41,8 +41,15 @@ void kvm_cpu__run(struct kvm_cpu *vcpu)
>>  		return;
>>
>>  	err = ioctl(vcpu->vcpu_fd, KVM_RUN, 0);
>> -	if (err < 0 && (errno != EINTR && errno != EAGAIN))
>> -		die_perror("KVM_RUN failed");
>> +	if (err < 0) {
>> +		if (errno == EINTR || errno == EAGAIN)
>> +			return;
>> +		else if (errno == EFAULT &&
>> +			 vcpu->kvm_run->exit_reason == KVM_EXIT_MEMORY_FAULT)
>> +			return;
>> +		else
>> +			die_perror("KVM_RUN failed");
>> +	}
>
> Probably cleaner to switch on errno?

This? . I will update.

	if (err < 0) {
		switch (errno) {
		case EINTR:
		case EAGAIN:
			return;
		case EFAULT:
			if (vcpu->kvm_run->exit_reason == KVM_EXIT_MEMORY_FAULT)
				return;
			/* fallthrough */
		default:
			die_perror("KVM_RUN failed");
		}
	}

-aneesh