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Tue, 15 Sep 2020 13:39:21 +0000 (GMT) Received: from oc4221205838.ibm.com (unknown [9.163.85.51]) by b03ledav002.gho.boulder.ibm.com (Postfix) with ESMTP; Tue, 15 Sep 2020 13:39:21 +0000 (GMT) Subject: Re: [PATCH v2 1/3] vfio: Find DMA available capability To: =?UTF-8?Q?Philippe_Mathieu-Daud=c3=a9?= , alex.williamson@redhat.com, cohuck@redhat.com References: <1600122570-12941-1-git-send-email-mjrosato@linux.ibm.com> <1600122570-12941-2-git-send-email-mjrosato@linux.ibm.com> From: Matthew Rosato Message-ID: <433aee24-84eb-527b-189e-f312054cb214@linux.ibm.com> Date: Tue, 15 Sep 2020 09:39:20 -0400 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.11.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 8bit X-TM-AS-GCONF: 00 X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:6.0.235, 18.0.687 definitions=2020-09-15_08:2020-09-15, 2020-09-15 signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 malwarescore=0 spamscore=0 phishscore=0 lowpriorityscore=0 mlxscore=0 adultscore=0 suspectscore=0 clxscore=1015 impostorscore=0 mlxlogscore=999 priorityscore=1501 bulkscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2006250000 definitions=main-2009150109 Received-SPF: pass client-ip=148.163.156.1; envelope-from=mjrosato@linux.ibm.com; helo=mx0a-001b2d01.pphosted.com X-detected-operating-system: by eggs.gnu.org: First seen = 2020/09/15 09:39:26 X-ACL-Warn: Detected OS = Linux 3.x [generic] [fuzzy] X-Spam_score_int: -26 X-Spam_score: -2.7 X-Spam_bar: -- X-Spam_report: (-2.7 / 5.0 requ) BAYES_00=-1.9, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_EF=-0.1, NICE_REPLY_A=-0.001, RCVD_IN_DNSWL_LOW=-0.7, RCVD_IN_MSPIKE_H2=-0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: thuth@redhat.com, pmorel@linux.ibm.com, schnelle@linux.ibm.com, david@redhat.com, qemu-devel@nongnu.org, pasic@linux.ibm.com, borntraeger@de.ibm.com, qemu-s390x@nongnu.org, rth@twiddle.net Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On 9/15/20 2:14 AM, Philippe Mathieu-Daudé wrote: > Hi Matthew, > > On 9/15/20 12:29 AM, Matthew Rosato wrote: >> The underlying host may be limiting the number of outstanding DMA >> requests for type 1 IOMMU. Add helper functions to check for the >> DMA available capability and retrieve the current number of DMA >> mappings allowed. >> >> Signed-off-by: Matthew Rosato >> --- >> hw/vfio/common.c | 37 +++++++++++++++++++++++++++++++++++++ >> include/hw/vfio/vfio-common.h | 2 ++ >> 2 files changed, 39 insertions(+) >> >> diff --git a/hw/vfio/common.c b/hw/vfio/common.c >> index 3335714..7f4a338 100644 >> --- a/hw/vfio/common.c >> +++ b/hw/vfio/common.c >> @@ -844,6 +844,43 @@ vfio_get_region_info_cap(struct vfio_region_info *info, uint16_t id) >> return NULL; >> } >> >> +static struct vfio_info_cap_header * >> +vfio_get_iommu_type1_info_cap(struct vfio_iommu_type1_info *info, uint16_t id) >> +{ >> + struct vfio_info_cap_header *hdr; >> + void *ptr = info; >> + >> + if (!(info->flags & VFIO_IOMMU_INFO_CAPS)) { >> + return NULL; >> + } >> + >> + for (hdr = ptr + info->cap_offset; hdr != ptr; hdr = ptr + hdr->next) { >> + if (hdr->id == id) { >> + return hdr; >> + } >> + } >> + >> + return NULL; >> +} >> + >> +bool vfio_get_info_dma_avail(struct vfio_iommu_type1_info *info, >> + unsigned int *avail) >> +{ >> + struct vfio_info_cap_header *hdr; >> + struct vfio_iommu_type1_info_dma_avail *cap; >> + >> + /* If the capability cannot be found, assume no DMA limiting */ >> + hdr = vfio_get_iommu_type1_info_cap(info, >> + VFIO_IOMMU_TYPE1_INFO_DMA_AVAIL); >> + if (hdr == NULL || avail == NULL) { > > If you expect the caller to use avail=NULL, then why > return false when there is available information? I was not expecting the caller to use avail=NULL as there would be nowhere to stash the dma_avail count. But you're right, we can at least still know that the capability is enabled/disabled when avail=NULL. I can change this by returning true/false solely based upon the existence of the capability (whether or not hdr==NULL) while only updating the caller's *avail value when avail!=NULL. If that's no good, then the alternative would be an assert() > >> + return false; >> + } >> + >> + cap = (void *) hdr; >> + *avail = cap->avail; >> + return true; >> +} >> + >> static int vfio_setup_region_sparse_mmaps(VFIORegion *region, >> struct vfio_region_info *info) >> { >> diff --git a/include/hw/vfio/vfio-common.h b/include/hw/vfio/vfio-common.h >> index c78f3ff..661a380 100644 >> --- a/include/hw/vfio/vfio-common.h >> +++ b/include/hw/vfio/vfio-common.h >> @@ -178,6 +178,8 @@ VFIOGroup *vfio_get_group(int groupid, AddressSpace *as, Error **errp); >> void vfio_put_group(VFIOGroup *group); >> int vfio_get_device(VFIOGroup *group, const char *name, >> VFIODevice *vbasedev, Error **errp); >> +bool vfio_get_info_dma_avail(struct vfio_iommu_type1_info *info, >> + unsigned int *avail); >> >> extern const MemoryRegionOps vfio_region_ops; >> typedef QLIST_HEAD(VFIOGroupList, VFIOGroup) VFIOGroupList; >> >