From mboxrd@z Thu Jan 1 00:00:00 1970 From: Pierre Morel Subject: Re: [PATCH v6 4/7] vfio: ap: register IOMMU VFIO notifier Date: Fri, 29 Mar 2019 10:31:08 +0100 Message-ID: <7a4bf9f1-5046-5838-a50d-8402782c880f@linux.ibm.com> References: <1553265828-27823-1-git-send-email-pmorel@linux.ibm.com> <1553265828-27823-5-git-send-email-pmorel@linux.ibm.com> <1731fb82-7877-9018-d12e-fd0e2406ac19@linux.ibm.com> Reply-To: pmorel@linux.ibm.com Mime-Version: 1.0 Content-Type: text/plain; charset="utf-8"; format="flowed" Content-Transfer-Encoding: 8bit Return-path: In-Reply-To: <1731fb82-7877-9018-d12e-fd0e2406ac19@linux.ibm.com> Content-Language: en-US Sender: linux-kernel-owner@vger.kernel.org List-Archive: List-Post: To: Tony Krowiak , borntraeger@de.ibm.com Cc: alex.williamson@redhat.com, cohuck@redhat.com, linux-kernel@vger.kernel.org, linux-s390@vger.kernel.org, kvm@vger.kernel.org, frankja@linux.ibm.com, pasic@linux.ibm.com, david@redhat.com, schwidefsky@de.ibm.com, heiko.carstens@de.ibm.com, freude@linux.ibm.com, mimu@linux.ibm.com List-ID: On 28/03/2019 21:46, Tony Krowiak wrote: > On 3/22/19 10:43 AM, Pierre Morel wrote: >> To be able to use the VFIO interface to facilitate the >> mediated device memory pinning/unpinning we need to register >> a notifier for IOMMU. >> >> While we will start to pin one guest page for the interrupt indicator >> byte, this is still ok with ballooning as this page will never be >> used by the guest virtio-balloon driver. >> So the pinned page will never be freed. And even a broken guest does >> so, that would not impact the host as the original page is still >> in control by vfio. > > I apologize, but I do not understand what you are saying in the second > sentence of the paragraph above. Why will the pinned page never be > freed? Because it is in use by the guest's kernel as a notification information byte for the original PQAP AQIC. I understand that the pinned page is under the control of vfio > until it is freed, but have no idea what you mean by "and even a broken > guest does so"? A broken guest does what? Can you please reword this so > it makes more sense? A broken guest could free the page used for the NIB. What is obviously wrong. > >> >> Signed-off-by: Pierre Morel >> Reviewed-by: Cornelia Huck >> --- >>   drivers/s390/crypto/vfio_ap_ops.c     | 38 >> +++++++++++++++++++++++++++++++++++ >>   drivers/s390/crypto/vfio_ap_private.h |  2 ++ >>   2 files changed, 40 insertions(+) >> >> diff --git a/drivers/s390/crypto/vfio_ap_ops.c >> b/drivers/s390/crypto/vfio_ap_ops.c >> index bdb36e0..3478499 100644 >> --- a/drivers/s390/crypto/vfio_ap_ops.c >> +++ b/drivers/s390/crypto/vfio_ap_ops.c >> @@ -787,6 +787,35 @@ static const struct attribute_group >> *vfio_ap_mdev_attr_groups[] = { >>       NULL >>   }; >> +/** >> + * vfio_ap_mdev_iommu_notifier: IOMMU notifier callback >> + * >> + * @nb: The notifier block >> + * @action: Action to be taken >> + * @data: data associated with the request >> + * >> + * For an UNMAP request, unpin the guest IOVA (the NIB guest address we >> + * pinned before). Other requests are ignored. >> + * >> + */ >> +static int vfio_ap_mdev_iommu_notifier(struct notifier_block *nb, >> +                       unsigned long action, void *data) >> +{ >> +    struct ap_matrix_mdev *matrix_mdev; >> + >> +    matrix_mdev = container_of(nb, struct ap_matrix_mdev, >> iommu_notifier); >> + > > I don't understand why we registered this notifier. I may be wrong, but > AFAIU, this notifier will be invoked only when the VFIO_IOMMU_UNMAP_DMA > ioctl is called from userspace. I did an experiment and inserted some > printf's to see if this ever gets called and verified it does not. Maybe > you have a good reason of which I'm not aware. Can you enlighten me > here? The vfio_iommu_type1 pin page requires a notifier. Regards, Pierre -- Pierre Morel Linux/KVM/QEMU in Böblingen - Germany