Hi Alexandru,
On 1/12/21 3:55 PM, Alexandru Elisei wrote:
> Hi Eric,
>
> On 12/12/20 6:50 PM, Eric Auger wrote:
>> has_run_once is set to true at the beginning of
>> kvm_vcpu_first_run_init(). This generally is not an issue
>> except when exercising the code with KVM selftests. Indeed,
>> if kvm_vgic_map_resources() fails due to erroneous user settings,
>> has_run_once is set and this prevents from continuing
>> executing the test. This patch moves the assignment after the
>> kvm_vgic_map_resources().
>>
>> Signed-off-by: Eric Auger <eric.auger@xxxxxxxxxx>
>> ---
>> arch/arm64/kvm/arm.c | 4 ++--
>> 1 file changed, 2 insertions(+), 2 deletions(-)
>>
>> diff --git a/arch/arm64/kvm/arm.c b/arch/arm64/kvm/arm.c
>> index c0ffb019ca8b..331fae6bff31 100644
>> --- a/arch/arm64/kvm/arm.c
>> +++ b/arch/arm64/kvm/arm.c
>> @@ -540,8 +540,6 @@ static int kvm_vcpu_first_run_init(struct kvm_vcpu *vcpu)
>> if (!kvm_arm_vcpu_is_finalized(vcpu))
>> return -EPERM;
>>
>> - vcpu->arch.has_run_once = true;
>> -
>> if (likely(irqchip_in_kernel(kvm))) {
>> /*
>> * Map the VGIC hardware resources before running a vcpu the
>> @@ -560,6 +558,8 @@ static int kvm_vcpu_first_run_init(struct kvm_vcpu *vcpu)
>> static_branch_inc(&userspace_irqchip_in_use);
>> }
>>
>> + vcpu->arch.has_run_once = true;
>
> I have a few concerns regarding this:
>
> 1. Moving has_run_once = true here seems very arbitrary to me - kvm_timer_enable()
> and kvm_arm_pmu_v3_enable(), below it, can both fail because of erroneous user
> values. If there's a reason why the assignment cannot be moved at the end of the
> function, I think it should be clearly stated in a comment for the people who
> might be tempted to write similar tests for the timer or pmu.
Setting has_run_once = true at the entry of the function looks to me
even more arbitrary. I agree with you that eventually has_run_once may
be moved at the very end but maybe this can be done later once timer,
pmu tests haven ben written
>
> 2. There are many ways that kvm_vgic_map_resources() can fail, other than
> incorrect user settings. I started digging into how
> kvm_vgic_map_resources()->vgic_v2_map_resources() can fail for a VGIC V2 and this
> is what I managed to find before I gave up:
>
> * vgic_init() can fail in:
> - kvm_vgic_dist_init()
> - vgic_v3_init()
> - kvm_vgic_setup_default_irq_routing()
> * vgic_register_dist_iodev() can fail in:
> - vgic_v3_init_dist_iodev()
> - kvm_io_bus_register_dev()(*)
> * kvm_phys_addr_ioremap() can fail in:
> - kvm_mmu_topup_memory_cache()
> - kvm_pgtable_stage2_map()
I changed the commit msg so that "incorrect user settings" sounds as an
example.
>
> So if any of the functions below fail, are we 100% sure it is safe to allow the
> user to execute kvm_vgic_map_resources() again?
I think additional tests will confirm this. However at the moment,
moving the assignment, which does not look wrong to me, allows to
greatly simplify the tests so I would tend to say that it is worth.
>
> (*) It looks to me like kvm_io_bus_register_dev() doesn't take into account a
> caller that tries to register the same device address range and it will create
> another identical range. Is this intentional? Is it a bug that should be fixed? Or
> am I misunderstanding the function?
doesn't kvm_io_bus_cmp() do the check?
Thanks
Eric
>
> Thanks,
> Alex
>> +
>> ret = kvm_timer_enable(vcpu);
>> if (ret)
>> return ret;
>
