Messages in this thread | | | Subject | Re: [PATCH v4 08/15] KVM: s390: interfaces to (de)configure guest's AP matrix | From | Tony Krowiak <> | Date | Mon, 7 May 2018 10:14:48 -0400 |
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On 05/03/2018 12:01 PM, Pierre Morel wrote: > On 03/05/2018 16:41, Tony Krowiak wrote: >> On 05/02/2018 10:57 AM, Pierre Morel wrote: >>> On 25/04/2018 18:21, Tony Krowiak wrote: >>>> On 04/23/2018 09:46 AM, Pierre Morel wrote: >>>>> On 15/04/2018 23:22, Tony Krowiak wrote: >>>>>> Provides interfaces to assign AP adapters, usage domains >>>>>> and control domains to a KVM guest. > ... >> The kvm_ap_configure_matrix(kvm, matrix) interface configures the >> APM, AQM and ADM in the >> guest's CRYCB which implies AP instructions are being interpreted. >> There is nothing in SIE >> precluding the sharing of AP queues between guests using SIE to >> interpret AP instructions, >> it is my opinion - along with several others - that this is not >> advisable given the >> results are not predictable, not to mention the security concerns. If >> the protocol to access >> queues changes, then we create a different interface. The other >> option is to include a flag >> on the kvm_ap_configure_matrix(kvm, matrix) interface to indicate >> whether sharing is >> allowed. I don't like this, because we have no way of knowing if the >> caller has taken the >> proper care to ensure the VM sharing the queue should be allowed >> access. Besides, when >> queue sharing is implemented, it is my opinion that we will intercept >> the AP instructions >> and the matrix will not be configured in the CRYCB. I stick by my >> response above. > > I mean, validating the queue sharing is a mater of the VFIO driver. > This code is not needed if the VFIO driver is not used. > But it is not very important.
Yes, this check could have been implemented in the VFIO driver, but as I stated above, that would require the driver to "know" the internals of KVM. I think the KVM logic should be encapsulated in KVM. If we want to allow sharing of interpreted AP devices, then we can always add a flag to the interface.
> > >> >>> >>>>>> +static int kvm_ap_matrix_apm_create(struct kvm_ap_matrix >>>>>> *ap_matrix, >>>>>> + struct ap_config_info *config) >>>>>> +{ >>>>>> + int apm_max = (config && config->apxa) ? config->Na + 1 : 16; >>>>> >>>>> At this moment you already know the format of the crycb. >>>> >>>> How? >>> >>> you calculated this in kvm_ap_build_crycbd() which is called from >>> kvm_s390_crypto_init() >>> itself called from kvm_arch_init_vm(). >>> It is when starting the VM. >> >> This structure is used by the vfio_ap driver to store the mediated >> matrix device's matrix >> configuration as well as to configure the CRYCB. The mediated >> device's matrix is >> configured before the guest is started ... it is the means for >> configuring the guest's >> matrix after all. The bottom line is, this function will be called >> long before the >> kvm_ap_build_crycbd() function is called. > > you are right, I was thinking about open, should have take more > attention. > Sorry. > > Pierre >
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