From: David Hildenbrand <david@redhat.com>
To: Christian Borntraeger <borntraeger@de.ibm.com>,
Eric Farman <farman@linux.ibm.com>,
Halil Pasic <pasic@linux.ibm.com>,
Cornelia Huck <cohuck@redhat.com>, Thomas Huth <thuth@redhat.com>
Cc: qemu-s390x@nongnu.org,
Richard Henderson <richard.henderson@linaro.org>,
qemu-devel@nongnu.org, Janosch Frank <frankja@linux.ibm.com>
Subject: Re: [RFC PATCH v1 2/2] s390x/kvm: Pass SIGP Stop flags
Date: Mon, 11 Oct 2021 11:21:29 +0200 [thread overview]
Message-ID: <fd2325a4-7c3a-b677-d259-b3731da507a2@redhat.com> (raw)
In-Reply-To: <28832611-02f0-7e52-6f15-39427c96d8bf@de.ibm.com>
On 11.10.21 10:40, Christian Borntraeger wrote:
>
>
> Am 11.10.21 um 09:09 schrieb David Hildenbrand:
>> On 08.10.21 22:38, Eric Farman wrote:
>>> When building a Stop IRQ to pass to KVM, we should incorporate
>>> the flags if handling the SIGP Stop and Store Status order.
>>> With that, KVM can reject other orders that are submitted for
>>> the same CPU while the operation is fully processed.
>>>
>>> Signed-off-by: Eric Farman <farman@linux.ibm.com>
>>> Acked-by: Janosch Frank <frankja@linux.ibm.com>
>>> ---
>>> target/s390x/kvm/kvm.c | 4 ++++
>>> 1 file changed, 4 insertions(+)
>>>
>>> diff --git a/target/s390x/kvm/kvm.c b/target/s390x/kvm/kvm.c
>>> index 5b1fdb55c4..701b9ddc88 100644
>>> --- a/target/s390x/kvm/kvm.c
>>> +++ b/target/s390x/kvm/kvm.c
>>> @@ -2555,6 +2555,10 @@ void kvm_s390_stop_interrupt(S390CPU *cpu)
>>> .type = KVM_S390_SIGP_STOP,
>>> };
>>> + if (cpu->env.sigp_order == SIGP_STOP_STORE_STATUS) {
>>> + irq.u.stop.flags = KVM_S390_STOP_FLAG_STORE_STATUS;
>>> + }
>>> +
>>
>> KVM_S390_STOP_FLAG_STORE_STATUS tells KVM to perform the store status as well ... is that really what we want?
> At least it should not hurt I guess. QEMU then does it again?
The thing is, that before we officially completed the action in user
space (and let other SIGP actions actually succeed in user space on the
CPU), the target CPU will be reported as !busy in the kernel already.
And before we even inject the stop interrupt, the CPU will be detected
as !busy in the kernel. I guess it will fix some cases where we poll via
SENSE if the stop and store happened, because the store *did* happen in
the kernel and we'll simply store again in user space.
However, I wonder if we want to handle it more generically: Properly
flag a CPU as busy for SIGP when we start processing the order until we
completed processing the order. That would allow to handle other SIGP
operations in user space cleanly, without any chance for races with
SENSE code running in the kernel.
--
Thanks,
David / dhildenb
next prev parent reply other threads:[~2021-10-11 9:23 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-10-08 20:38 [RFC PATCH v1 0/2] Improvements to SIGP handling [QEMU] Eric Farman
2021-10-08 20:38 ` [RFC PATCH v1 1/2] s390x: sigp: Force Set Architecture to return Invalid Parameter Eric Farman
2021-10-09 5:40 ` Thomas Huth
2021-10-11 7:04 ` David Hildenbrand
2021-10-08 20:38 ` [RFC PATCH v1 2/2] s390x/kvm: Pass SIGP Stop flags Eric Farman
2021-10-11 7:09 ` David Hildenbrand
2021-10-11 8:40 ` Christian Borntraeger
2021-10-11 9:21 ` David Hildenbrand [this message]
2021-10-11 17:58 ` Eric Farman
2021-10-11 18:07 ` David Hildenbrand
2021-10-12 6:58 ` [RFC PATCH v1 0/2] Improvements to SIGP handling [QEMU] Thomas Huth
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