From: David Hildenbrand <david@redhat.com>
To: Christian Borntraeger <borntraeger@de.ibm.com>,
Cornelia Huck <cohuck@redhat.com>,
Janis Schoetterl-Glausch <scgl@linux.ibm.com>,
Janosch Frank <frankja@linux.ibm.com>,
Heiko Carstens <hca@linux.ibm.com>,
Vasily Gorbik <gor@linux.ibm.com>
Cc: Claudio Imbrenda <imbrenda@linux.ibm.com>,
"open list:KERNEL VIRTUAL MACHINE for s390 (KVM/s390)"
<kvm@vger.kernel.org>,
"open list:S390" <linux-s390@vger.kernel.org>,
open list <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH] KVM: s390: Enable specification exception interpretation
Date: Tue, 6 Jul 2021 13:59:51 +0200 [thread overview]
Message-ID: <be78ce5d-92e4-36bd-aa28-e32db0342a44@redhat.com> (raw)
In-Reply-To: <194128c1-8886-5b8b-2249-5ec58b8e7adb@de.ibm.com>
On 06.07.21 13:56, Christian Borntraeger wrote:
>
>
> On 06.07.21 13:52, Cornelia Huck wrote:
>> On Tue, Jul 06 2021, Janis Schoetterl-Glausch <scgl@linux.ibm.com> wrote:
>>
>>> When this feature is enabled the hardware is free to interpret
>>> specification exceptions generated by the guest, instead of causing
>>> program interruption interceptions.
>>>
>>> This benefits (test) programs that generate a lot of specification
>>> exceptions (roughly 4x increase in exceptions/sec).
>>>
>>> Interceptions will occur as before if ICTL_PINT is set,
>>> i.e. if guest debug is enabled.
>>>
>>> Signed-off-by: Janis Schoetterl-Glausch <scgl@linux.ibm.com>
>>> ---
>>> I'll additionally send kvm-unit-tests for testing this feature.
>>>
>>> arch/s390/include/asm/kvm_host.h | 1 +
>>> arch/s390/kvm/kvm-s390.c | 2 ++
>>> arch/s390/kvm/vsie.c | 2 ++
>>> 3 files changed, 5 insertions(+)
>>
>> (...)
>>
>>> diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c
>>> index b655a7d82bf0..aadd589a3755 100644
>>> --- a/arch/s390/kvm/kvm-s390.c
>>> +++ b/arch/s390/kvm/kvm-s390.c
>>> @@ -3200,6 +3200,8 @@ static int kvm_s390_vcpu_setup(struct kvm_vcpu *vcpu)
>>> vcpu->arch.sie_block->ecb |= ECB_SRSI;
>>> if (test_kvm_facility(vcpu->kvm, 73))
>>> vcpu->arch.sie_block->ecb |= ECB_TE;
>>> + if (!kvm_is_ucontrol(vcpu->kvm))
>>> + vcpu->arch.sie_block->ecb |= ECB_SPECI;
>>
>> Does this exist for any hardware version (i.e. not guarded by a cpu
>> feature?)
>
> Not for all hardware versions, but also no indication. The architecture
> says that the HW is free to do this or not. (which makes the vsie code
> simpler).
I remember the architecture said at some point to never set undefined
bits - and this bit is undefined on older HW generations. I might be
wrong, though.
(I though HW learned the lesson to always use proper feature indications
along with new features)
--
Thanks,
David / dhildenb
next prev parent reply other threads:[~2021-07-06 12:12 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-07-06 11:47 [PATCH] KVM: s390: Enable specification exception interpretation Janis Schoetterl-Glausch
2021-07-06 11:52 ` Cornelia Huck
2021-07-06 11:56 ` Christian Borntraeger
2021-07-06 11:59 ` David Hildenbrand [this message]
2021-07-06 12:02 ` Christian Borntraeger
2021-07-06 15:16 ` David Hildenbrand
2021-07-06 15:27 ` Janis Schoetterl-Glausch
2021-07-07 7:26 ` David Hildenbrand
2021-07-06 11:55 ` David Hildenbrand
2021-07-07 8:30 ` Christian Borntraeger
2021-07-07 8:54 ` Cornelia Huck
2021-07-07 9:55 ` Janis Schoetterl-Glausch
2021-07-07 11:42 ` Cornelia Huck
2021-07-07 8:56 ` Janis Schoetterl-Glausch
2021-07-07 8:59 ` Christian Borntraeger
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