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From: Tony Krowiak <akrowiak@linux.ibm.com>
To: Halil Pasic <pasic@linux.ibm.com>
Cc: linux-s390@vger.kernel.org, linux-kernel@vger.kernel.org,
	kvm@vger.kernel.org, borntraeger@de.ibm.com, cohuck@redhat.com,
	alex.williamson@redhat.com, kwankhede@nvidia.com,
	david@redhat.com, Janosch Frank <frankja@linux.ibm.com>
Subject: Re: [PATCH] s390/vfio-ap: Clean up vfio_ap resources when KVM pointer invalidated
Date: Mon, 7 Dec 2020 13:50:36 -0500	[thread overview]
Message-ID: <683dd341-f047-0447-1ee8-c126c305b6c2@linux.ibm.com> (raw)
In-Reply-To: <20201204200502.1c34ae58.pasic@linux.ibm.com>



On 12/4/20 2:05 PM, Halil Pasic wrote:
> On Fri, 4 Dec 2020 09:43:59 -0500
> Tony Krowiak <akrowiak@linux.ibm.com> wrote:
>
>>>> +{
>>>> +	if (matrix_mdev->kvm) {
>>>> +		(matrix_mdev->kvm);
>>>> +		matrix_mdev->kvm->arch.crypto.pqap_hook = NULL;
>>> Is a plain assignment to arch.crypto.pqap_hook apropriate, or do we need
>>> to take more care?
>>>
>>> For instance kvm_arch_crypto_set_masks() takes kvm->lock before poking
>>> kvm->arch.crypto.crycb.
>> I do not think so. The CRYCB is used by KVM to provide crypto resources
>> to the guest so it makes sense to protect it from changes to it while
>> passing
>> the AP devices through to the guest. The hook is used only when an AQIC
>> executed on the guest is intercepted by KVM. If the notifier
>> is being invoked to notify vfio_ap that KVM has been set to NULL, this means
>> the guest is gone in which case there will be no AP instructions to
>> intercept.
> If the update to pqap_hook isn't observed as atomic we still have a
> problem. With torn writes or reads we would try to use a corrupt function
> pointer. While the compiler probably ain't likely to generate silly code
> for the above assignment (multiple write instructions less then
> quadword wide), I know of nothing that would prohibit the compiler to do
> so.

I'm sorry, but I still don't understand why you think this is a problem
given what I stated above.

>
> I'm not certain about the scope of the kvm->lock (if it's supposed to
> protect the whole sub-tree of objects). Maybe Janosch can help us out.
> @Janosch: what do you think?
>
> Regards,
> Halil


  parent reply	other threads:[~2020-12-07 18:51 UTC|newest]

Thread overview: 21+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-12-02 23:41 [PATCH] s390/vfio-ap: Clean up vfio_ap resources when KVM pointer invalidated Tony Krowiak
2020-12-03 10:19 ` Cornelia Huck
2020-12-03 17:01   ` Halil Pasic
2020-12-03 19:14     ` Tony Krowiak
2020-12-03 17:55 ` Halil Pasic
2020-12-04 14:43   ` Tony Krowiak
2020-12-04 19:05     ` Halil Pasic
2020-12-04 19:46       ` Tony Krowiak
2020-12-04 21:54         ` Halil Pasic
2020-12-07 18:50       ` Tony Krowiak [this message]
2020-12-08  0:01         ` Halil Pasic
     [not found]           ` <e196b743-74d8-398b-4b3e-4a64002d9bfc@linux.ibm.com>
2020-12-13 22:57             ` Halil Pasic
2020-12-04 16:48   ` Tony Krowiak
2020-12-04 16:57     ` Cornelia Huck
2020-12-04 19:47       ` Tony Krowiak
2020-12-07 15:24     ` Halil Pasic
2020-12-07 15:42       ` Christian Borntraeger
2020-12-07 19:05 ` Tony Krowiak
2020-12-08  0:40   ` Halil Pasic
2020-12-11 21:08     ` Tony Krowiak
2020-12-13 23:13       ` Halil Pasic

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