From: Pierre Morel <pmorel@linux.ibm.com>
To: Janis Schoetterl-Glausch <scgl@linux.ibm.com>, kvm@vger.kernel.org
Cc: linux-s390@vger.kernel.org, linux-kernel@vger.kernel.org,
borntraeger@de.ibm.com, frankja@linux.ibm.com, cohuck@redhat.com,
david@redhat.com, thuth@redhat.com, imbrenda@linux.ibm.com,
hca@linux.ibm.com, gor@linux.ibm.com, wintera@linux.ibm.com,
seiden@linux.ibm.com, nrb@linux.ibm.com
Subject: Re: [PATCH v10 2/3] KVM: s390: guest support for topology function
Date: Tue, 28 Jun 2022 16:13:00 +0200 [thread overview]
Message-ID: <7924cf38-83cb-5d5c-9ad9-a4faaa89f9d5@linux.ibm.com> (raw)
In-Reply-To: <851dd253-8412-ed5f-3a97-980b3a3850cc@linux.ibm.com>
On 6/28/22 14:18, Janis Schoetterl-Glausch wrote:
> On 6/28/22 12:58, Pierre Morel wrote:
>>
>>
>> On 6/28/22 10:59, Janis Schoetterl-Glausch wrote:
>>> On 6/20/22 14:54, Pierre Morel wrote:
>>>> We report a topology change to the guest for any CPU hotplug.
>>>>
>>>> The reporting to the guest is done using the Multiprocessor
>>>> Topology-Change-Report (MTCR) bit of the utility entry in the guest's
>>>> SCA which will be cleared during the interpretation of PTF.
>>>>
>>>> On every vCPU creation we set the MCTR bit to let the guest know the
>>>> next time he uses the PTF with command 2 instruction that the
>>>> topology changed and that he should use the STSI(15.1.x) instruction
>>>> to get the topology details.
>>>>
>>>> STSI(15.1.x) gives information on the CPU configuration topology.
>>>> Let's accept the interception of STSI with the function code 15 and
>>>> let the userland part of the hypervisor handle it when userland
>>>> support the CPU Topology facility.
>>>>
>>>> Signed-off-by: Pierre Morel <pmorel@linux.ibm.com>
>>>> ---
>>>> arch/s390/include/asm/kvm_host.h | 11 ++++++++---
>>>> arch/s390/kvm/kvm-s390.c | 27 ++++++++++++++++++++++++++-
>>>> arch/s390/kvm/priv.c | 15 +++++++++++----
>>>> arch/s390/kvm/vsie.c | 3 +++
>>>> 4 files changed, 48 insertions(+), 8 deletions(-)
>>>>
>>> [...]
>>>
>>>> diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c
>>>> index 8fcb56141689..95b96019ca8e 100644
>>>> --- a/arch/s390/kvm/kvm-s390.c
>>>> +++ b/arch/s390/kvm/kvm-s390.c
>>>> @@ -1691,6 +1691,25 @@ static int kvm_s390_get_cpu_model(struct kvm *kvm, struct kvm_device_attr *attr)
>>>> return ret;
>>>> }
>>>>
>>>> +/**
>>>> + * kvm_s390_sca_set_mtcr
>>>
>>> I wonder if there is a better name, kvm_s390_report_topology_change maybe?
>>>
>>>> + * @kvm: guest KVM description
>>>> + *
>>>> + * Is only relevant if the topology facility is present,
>>>> + * the caller should check KVM facility 11
>>>> + *
>>>> + * Updates the Multiprocessor Topology-Change-Report to signal
>>>> + * the guest with a topology change.
>>>> + */
>>>> +static void kvm_s390_sca_set_mtcr(struct kvm *kvm)
>>>> +{
>>>
>>> Do we need a sca_lock read_section here? If we don't why not?
>>> Did not see one up the stack, but I might have overlooked something.
>>
>> Yes we do.
>> As I said about your well justified comment in a previous mail, ipte_lock is not the right thing to use here and I will replace with an inter locked update.
>
> Not sure I'm understanding you right, you're saying we need both? i.e.:
>
> struct bsca_block *sca;
>
> read_lock(&vcpu->kvm->arch.sca_lock);
> sca = kvm->arch.sca;
> atomic_or(SCA_UTILITY_MTCR, &sca->utility);
> read_unlock(&vcpu->kvm->arch.sca_lock);
>
> Obviously you would need to change the definition of the utility field and could not use a bit field like Janosch
> suggested, unless you want to use a cmpxchg loop.
> It's a bit ugly that utility is a two byte value.
> Maybe there is a nicer way to set that bit, OR (OI, OIY) seem appropriate, but I don't know if they have a nice
> abstraction in Linux or if you'd need inline asm.
I was think to something like this because it is what is used most of
the time when a bit is to be change concurrently with firmware.
+union sca_utility {
+ __u16 val;
+ struct {
+ __u16 mtcr : 1;
+ __u16 reserved : 15;
+ };
+};
+
struct bsca_block {
union ipte_control ipte_control;
__u64 reserved[5];
__u64 mcn;
- __u64 reserved2;
+ union sca_utility utility;
+ __u8 reserved2[6];
struct bsca_entry cpu[KVM_S390_BSCA_CPU_SLOTS];
}
....
static void kvm_s390_sca_set_mtcr(struct kvm *kvm, int val)
{
struct bsca_block *sca = kvm->arch.sca;
union sca_utility new, old;
read_lock(&kvm->arch.sca_lock);
do {
old = READ_ONCE(sca->utility);
new = old;
new.mtcr = val ? 1 : 0;
} while (cmpxchg(&sca->utility.val, old.val, new.val) != old.val);
read_lock(&kvm->arch.sca_lock);
}
>>
>>>
>>>> + struct bsca_block *sca = kvm->arch.sca; /* SCA version doesn't matter */
>>>> +
>>>> + ipte_lock(kvm);
>>>> + sca->utility |= SCA_UTILITY_MTCR;
>>>> + ipte_unlock(kvm);
>>>> +}
>>>> +
>>>
>>> [...]
>>>
>>
>
--
Pierre Morel
IBM Lab Boeblingen
next prev parent reply other threads:[~2022-06-28 14:08 UTC|newest]
Thread overview: 29+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-06-20 12:54 [PATCH v10 0/3] s390x: KVM: CPU Topology Pierre Morel
2022-06-20 12:54 ` [PATCH v10 1/3] KVM: s390: ipte lock for SCA access should be contained in KVM Pierre Morel
2022-06-24 5:47 ` Janosch Frank
2022-06-27 13:29 ` Pierre Morel
2022-06-24 6:57 ` Nico Boehr
2022-06-27 13:28 ` Pierre Morel
2022-06-24 9:22 ` Claudio Imbrenda
2022-06-20 12:54 ` [PATCH v10 2/3] KVM: s390: guest support for topology function Pierre Morel
2022-06-24 6:22 ` Janosch Frank
2022-06-27 13:30 ` Pierre Morel
2022-06-24 6:56 ` Nico Boehr
2022-06-27 13:16 ` Pierre Morel
2022-06-28 14:38 ` Pierre Morel
2022-06-24 9:32 ` Claudio Imbrenda
2022-06-27 17:40 ` Pierre Morel
2022-06-24 15:09 ` Janis Schoetterl-Glausch
2022-06-27 14:36 ` Pierre Morel
2022-06-28 8:59 ` Janis Schoetterl-Glausch
2022-06-28 10:58 ` Pierre Morel
2022-06-28 12:18 ` Janis Schoetterl-Glausch
2022-06-28 14:13 ` Pierre Morel [this message]
2022-06-28 15:01 ` Janis Schoetterl-Glausch
2022-06-28 15:44 ` Pierre Morel
2022-06-28 10:59 ` Pierre Morel
2022-06-20 12:54 ` [PATCH v10 3/3] KVM: s390: resetting the Topology-Change-Report Pierre Morel
2022-06-24 6:50 ` Janosch Frank
2022-06-27 13:34 ` Pierre Morel
2022-06-28 16:41 ` Janis Schoetterl-Glausch
2022-06-28 17:27 ` Pierre Morel
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