Messages in this thread | | | Subject | Re: [PATCH v5 06/13] KVM: s390: interfaces to manage guest's AP matrix | From | Tony Krowiak <> | Date | Mon, 21 May 2018 11:23:51 -0400 |
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On 05/16/2018 10:41 AM, Pierre Morel wrote: > On 16/05/2018 16:29, Tony Krowiak wrote: >> On 05/11/2018 12:08 PM, Halil Pasic wrote: >>> >>> >>> On 05/07/2018 05:11 PM, Tony Krowiak wrote: >>>> Provides interfaces to manage the AP adapters, usage domains >>>> and control domains assigned to a KVM guest. >>>> >>>> The guest's SIE state description has a satellite structure called the >>>> Crypto Control Block (CRYCB) containing three bitmask fields >>>> identifying the adapters, queues (domains) and control domains >>>> assigned to the KVM guest: >>> >>> [..] >>> >>>> index 00bcfb0..98b53c7 100644 >>>> --- a/arch/s390/kvm/kvm-ap.c >>>> +++ b/arch/s390/kvm/kvm-ap.c >>>> @@ -7,6 +7,7 @@ >>> >>> [..] >>> >>>> + >>>> +/** >>>> + * kvm_ap_validate_queue_sharing >>>> + * >>>> + * Verifies that the APQNs derived from the cross product of the >>>> AP adapter IDs >>>> + * and AP queue indexes comprising the AP matrix are not >>>> configured for >>>> + * another guest. AP queue sharing is not allowed. >>>> + * >>>> + * @kvm: the KVM guest >>>> + * @matrix: the AP matrix >>>> + * >>>> + * Returns 0 if the APQNs are valid, otherwise; returns -EBUSY. >>>> + */ >>>> +static int kvm_ap_validate_queue_sharing(struct kvm *kvm, >>>> + struct kvm_ap_matrix *matrix) >>>> +{ >>>> + struct kvm *vm; >>>> + unsigned long *apm, *aqm; >>>> + unsigned long apid, apqi; >>>> + >>>> + >>>> + /* No other VM may share an AP Queue with the input VM */ >>>> + list_for_each_entry(vm, &vm_list, vm_list) { >>>> + if (kvm == vm) >>>> + continue; >>>> + >>>> + apm = kvm_ap_get_crycb_apm(vm); >>>> + if (!bitmap_and(apm, apm, matrix->apm, matrix->apm_max + 1)) >>>> + continue; >>>> + >>>> + aqm = kvm_ap_get_crycb_aqm(vm); >>>> + if (!bitmap_and(aqm, aqm, matrix->aqm, matrix->aqm_max + 1)) >>>> + continue; >>>> + >>>> + for_each_set_bit_inv(apid, apm, matrix->apm_max + 1) >>>> + for_each_set_bit_inv(apqi, aqm, matrix->aqm_max + 1) >>>> + kvm_ap_log_sharing_err(vm, apid, apqi); >>>> + >>>> + return -EBUSY; >>>> + } >>>> + >>>> + return 0; >>>> +} >>>> + >>>> +int kvm_ap_configure_matrix(struct kvm *kvm, struct kvm_ap_matrix >>>> *matrix) >>>> +{ >>>> + int ret = 0; >>>> + >>>> + mutex_lock(&kvm->lock); >>> >>> You seem to take only kvm->lock, vm_list however (used in >>> kvm_ap_validate_queue_sharing()) seems to be protected by >>> kvm_lock. >>> >>> Can you tell me why is this supposed to be safe? >>> >>> What is supposed to prevent an execution like >>> vm1: call kvm_ap_configure_matrix(m1) >>> vm2: call kvm_ap_configure_matrix(m2) >>> vm1: call kvm_ap_validate_queue_sharing(m1) >>> vm2: call kvm_ap_validate_queue_sharing(m2) >>> vm1: call kvm_ap_set_crycb_masks(m1) >>> vm2: call kvm_ap_set_crycb_masks(m2) >>> >>> where, let's say, m1 and m2 are equal in the sense that the >>> mask values are the same? >> >> vm1 will get the kvm->lock first in your scenario when >> kvm_ap_configure_matrix(m1) is invoked. Since the other >> functions - i.e., kvm_ap_validate_queue_sharing(m1) and >> kvm_ap_set_crycb_masks(m1) - are static and only called >> from the kvm_ap_configure_matrix(m1), your scenario >> can never happen because vm2 will not get the lock until >> kvm_ap_configure_matrix(m1) has completed. I see your >> point, however, and maybe I should also acquire the kvm_lock. > > AFAIU the locks you are talking about are KVM specific > but the example from Halil use two different VM, > i.e. two different locks are used and vm2 never wait for vw1.
Right you are! Perhaps I need to hold the kvm_lock, at least in the kvm_ap_validate_queue_sharing() function while looping over vm_list.
> > >> >>> >>> >>> Regards, >>> Halil >>> >>>> + >>>> + ret = kvm_ap_validate_queue_sharing(kvm, matrix); >>>> + if (ret) >>>> + goto done; >>>> + >>>> + kvm_ap_set_crycb_masks(kvm, matrix); >>>> + >>>> +done: >>>> + mutex_unlock(&kvm->lock); >>>> + >>>> + return ret; >>>> +} >>>> +EXPORT_SYMBOL(kvm_ap_configure_matrix); >>>> + >> >> >
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