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SubjectRe: [PATCH v3 03/14] KVM: s390: CPU model support for AP virtualization
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On 27/03/2018 12:59, Cornelia Huck wrote:
> On Wed, 14 Mar 2018 14:25:43 -0400
> Tony Krowiak <akrowiak@linux.vnet.ibm.com> wrote:
>
>> Introduces a new CPU model feature and two CPU model
>> facilities to support AP virtualization for KVM guests.
>>
>> CPU model feature:
>>
>> The KVM_S390_VM_CPU_FEAT_AP feature indicates that
>> AP instructions are available on the guest. This
>> feature will be enabled by the kernel only if the AP
>> instructions are installed on the linux host. This feature
>> must be specifically turned on for the KVM guest from
>> userspace to use the VFIO AP device driver for guest
>> access to AP devices.
>>
>> CPU model facilities:
>>
>> 1. AP Query Configuration Information (QCI) facility is installed.
>>
>> This is indicated by setting facilities bit 12 for
>> the guest. The kernel will not enable this facility
>> for the guest if it is not set on the host. This facility
>> must not be set by userspace if the KVM_S390_VM_CPU_FEAT_AP
>> feature is not installed.
>>
>> 2. AP Facilities Test facility (APFT) is installed.
>>
>> This is indicated by setting facilities bit 15 for
>> the guest. The kernel will not enable this facility for
>> the guest if it is not set on the host. This facility
>> must not be set by userspace if the KVM_S390_VM_CPU_FEAT_AP
>> feature is not installed.
>>
>> Reviewed-by: Christian Borntraeger <borntraeger@de.ibm.com>
>> Reviewed-by: Halil Pasic <pasic@linux.vnet.ibm.com>
>> Signed-off-by: Tony Krowiak <akrowiak@linux.vnet.ibm.com>
>> ---
>> arch/s390/include/asm/kvm_host.h | 1 +
>> arch/s390/include/uapi/asm/kvm.h | 1 +
>> arch/s390/kvm/kvm-s390.c | 4 ++++
>> arch/s390/tools/gen_facilities.c | 2 ++
>> 4 files changed, 8 insertions(+), 0 deletions(-)
>>
>> diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c
>> index c47731d..a60c45b 100644
>> --- a/arch/s390/kvm/kvm-s390.c
>> +++ b/arch/s390/kvm/kvm-s390.c
>> @@ -350,6 +350,10 @@ static void kvm_s390_cpu_feat_init(void)
>>
>> if (MACHINE_HAS_ESOP)
>> allow_cpu_feat(KVM_S390_VM_CPU_FEAT_ESOP);
>> +
>> + if (ap_instructions_installed()) /* AP instructions installed on host */
>> + allow_cpu_feat(KVM_S390_VM_CPU_FEAT_AP);
> That's another dependency of the base kvm-s390 module on zcrypt, which
> I don't like at all.

In fact there is a tricky thing about zcrypt it is that even it is
configured a a module
CONFIG_ZCRYPT=M, the AP BUS is built statically with the kernel.
See drivers/s390/crypto/Makefile
"
ap-objs := ap_bus.o ap_card.o ap_queue.o
obj-$(subst m,y,$(CONFIG_ZCRYPT)) += ap.o
"
ugly isn't it?

>
> There are two possibilities here:
> - Exposing the features makes sense even if no zcrypt driver is active
> in the host. Then, ap_instructions_installed() needs to be moved into
> always-built code (see my comments for the interface in patch 1).

This is what we need for future enhancement I think.

> - Exposing the features makes sense only if we actually want to make
> vfio-ap available. Then we should provide the proper check in the
> vfio-ap parts (which depends on zcrypt) and stub it out if vfio-ap is
> not configured.
>
>> +
>> /*
>> * We need SIE support, ESOP (PROT_READ protection for gmap_shadow),
>> * 64bit SCAO (SCA passthrough) and IDTE (for gmap_shadow unshadowing).


--
Pierre Morel
Linux/KVM/QEMU in Böblingen - Germany

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