Messages in this thread | | | Subject | Re: [PATCH v9 21/22] KVM: s390: CPU model support for AP virtualization | From | Halil Pasic <> | Date | Thu, 23 Aug 2018 12:00:46 +0200 |
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On 08/23/2018 09:44 AM, David Hildenbrand wrote: > On 22.08.2018 22:16, Tony Krowiak wrote: >> On 08/22/2018 07:24 AM, David Hildenbrand wrote: >>> On 22.08.2018 13:19, David Hildenbrand wrote: >>>> On 13.08.2018 23:48, Tony Krowiak wrote: >>>>> From: Tony Krowiak <akrowiak@linux.ibm.com> >>>>> >>>>> 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. >>>>> >>>>> If this facility is not set for the KVM guest, then only >>>>> APQNs with an APQI less than 16 will be used by a Linux >>>>> guest regardless of the matrix configuration for the virtual >>>>> machine. This is a limitation of the Linux AP bus. >>>>> >>>>> 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. >>>>> >>>>> If this facility is not set for the KVM guest, then no >>>>> AP devices will be available to the guest regardless of >>>>> the guest's matrix configuration for the virtual >>>>> machine. This is a limitation of the Linux AP bus. >>>>> >>>>> Signed-off-by: Tony Krowiak <akrowiak@linux.ibm.com> >>>>> Reviewed-by: Christian Borntraeger <borntraeger@de.ibm.com> >>>>> Reviewed-by: Halil Pasic <pasic@linux.ibm.com> >>>>> Tested-by: Michael Mueller <mimu@linux.ibm.com> >>>>> Tested-by: Farhan Ali <alifm@linux.ibm.com> >>>>> Signed-off-by: Christian Borntraeger <borntraeger@de.ibm.com> >>>>> --- >>>>> arch/s390/kvm/kvm-s390.c | 5 +++++ >>>>> arch/s390/tools/gen_facilities.c | 2 ++ >>>>> 2 files changed, 7 insertions(+), 0 deletions(-) >>>>> >>>>> diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c >>>>> index 1e8cb67..d5e04d2 100644 >>>>> --- a/arch/s390/kvm/kvm-s390.c >>>>> +++ b/arch/s390/kvm/kvm-s390.c >>>>> @@ -367,6 +367,11 @@ static void kvm_s390_cpu_feat_init(void) >>>>> >>>>> if (MACHINE_HAS_ESOP) >>>>> allow_cpu_feat(KVM_S390_VM_CPU_FEAT_ESOP); >>>>> + >>>>> + /* Check if AP instructions installed on host */ >>>>> + if (ap_instructions_available()) >>>>> + allow_cpu_feat(KVM_S390_VM_CPU_FEAT_AP); >>>>> + >>>>> /* >>>>> * We need SIE support, ESOP (PROT_READ protection for gmap_shadow), >>>>> * 64bit SCAO (SCA passthrough) and IDTE (for gmap_shadow unshadowing). >>>>> diff --git a/arch/s390/tools/gen_facilities.c b/arch/s390/tools/gen_facilities.c >>>>> index 90a8c9e..a52290b 100644 >>>>> --- a/arch/s390/tools/gen_facilities.c >>>>> +++ b/arch/s390/tools/gen_facilities.c >>>>> @@ -106,6 +106,8 @@ struct facility_def { >>>>> >>>>> .name = "FACILITIES_KVM_CPUMODEL", >>>>> .bits = (int[]){ >>>>> + 12, /* AP Query Configuration Information */ >>>>> + 15, /* AP Facilities Test */ >>>>> -1 /* END */ >>>>> } >>>>> }, >>>>> >>>> I really wonder if we should also export the APXA facility. >>>> >>>> We can probe and allow that CPU feature. However, we cannot disable it >>>> (as of now). >>>> >>>> We have other CPU features where it is the same case (basically all >>>> subfunctions). See kvm_s390_get_processor_subfunc(). We probe them and >>>> export them, but support to disable them has never been implemented. >>>> >>>> On a high level, we could then e.g. deny to start a QEMU guest if APXA >>>> is available but has been disabled. (until we know that disabling it >>>> actually works - if ever). >>>> >>>> This helps to catch nasty migration bugs (e.g. APXA suddenly >>>> disappearing). Although unlikely, definitely possible. >>>> >>>> >>>> Are there any other AP related facilities that the guest can from now on >>>> probe that should also become part of the CPU model? >>>> >>> To be more precise, shouldn't PQAP(QCI) be handled just like other >>> subfunctions? (I remember it should) >> >> When you suggest PQAP(QCI) be handled like other subfunctions, are you >> suggesting that there should be a field in struct kvm_s390_vm_cpu_subfunc >> with a bit indicating the QCI subfunction is available? The availability >> of the QCI subfunction of the PQAP instruction is determined by facilities >> bit 12. Is it not enough to export facilities bit 12? > > The feature block (128 bit) from PQAP(QCI) should be passed through a > subfunction block to QEMU. >
I'm confused, which 128 bit?
> So it is about passing e.g. APXA availability, not QCI itself. (as you > correctly said, that is stfl 12) >
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