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Tsirkin" To: CLEMENT MATHIEU--DRIF Cc: "qemu-devel@nongnu.org" , "jasowang@redhat.com" , "zhenzhong.duan@intel.com" , "kevin.tian@intel.com" , "yi.l.liu@intel.com" , "peterx@redhat.com" Subject: Re: [PATCH v5 2/2] intel_iommu: Take locks when looking for and creating address spaces Message-ID: <20250514074821-mutt-send-email-mst@kernel.org> References: <20250430124750.240412-1-clement.mathieu--drif@eviden.com> <20250430124750.240412-3-clement.mathieu--drif@eviden.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20250430124750.240412-3-clement.mathieu--drif@eviden.com> Received-SPF: pass client-ip=170.10.133.124; envelope-from=mst@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -37 X-Spam_score: -3.8 X-Spam_bar: --- X-Spam_report: (-3.8 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-1.686, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H5=0.001, RCVD_IN_MSPIKE_WL=0.001, RCVD_IN_VALIDITY_CERTIFIED_BLOCKED=0.001, RCVD_IN_VALIDITY_RPBL_BLOCKED=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: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org On Wed, Apr 30, 2025 at 12:48:06PM +0000, CLEMENT MATHIEU--DRIF wrote: > vtd_find_add_as can be called by multiple threads which leads to a race > condition. Taking the IOMMU lock ensures we avoid such a race. > Moreover we also need to take the bql to avoid an assert to fail in > memory_region_add_subregion_overlap when actually allocating a new > address space. > > Signed-off-by: Clement Mathieu--Drif > --- > hw/i386/intel_iommu.c | 25 ++++++++++++++++++++++++- > 1 file changed, 24 insertions(+), 1 deletion(-) > > diff --git a/hw/i386/intel_iommu.c b/hw/i386/intel_iommu.c > index dad1d9f300..144e25622a 100644 > --- a/hw/i386/intel_iommu.c > +++ b/hw/i386/intel_iommu.c > @@ -4205,9 +4205,30 @@ VTDAddressSpace *vtd_find_add_as(IntelIOMMUState *s, PCIBus *bus, > VTDAddressSpace *vtd_dev_as; > char name[128]; > > + vtd_iommu_lock(s); > vtd_dev_as = g_hash_table_lookup(s->vtd_address_spaces, &key); > + vtd_iommu_unlock(s); > + > if (!vtd_dev_as) { > - struct vtd_as_key *new_key = g_malloc(sizeof(*new_key)); > + struct vtd_as_key *new_key; > + /* Slow path */ > + > + /* > + * memory_region_add_subregion_overlap requires the bql, > + * make sure we own it. > + */ not how comments should look > + BQL_LOCK_GUARD(); > + vtd_iommu_lock(s); > + > + /* Check again as we released the lock for a moment */ > + vtd_dev_as = g_hash_table_lookup(s->vtd_address_spaces, &key); > + if (vtd_dev_as) { > + vtd_iommu_unlock(s); > + return vtd_dev_as; > + } > + > + /* Still nothing, allocate a new address space */ > + new_key = g_malloc(sizeof(*new_key)); > > new_key->bus = bus; > new_key->devfn = devfn; > @@ -4298,6 +4319,8 @@ VTDAddressSpace *vtd_find_add_as(IntelIOMMUState *s, PCIBus *bus, > vtd_switch_address_space(vtd_dev_as); > > g_hash_table_insert(s->vtd_address_spaces, new_key, vtd_dev_as); > + trailing whitespace here > + vtd_iommu_unlock(s); > } > return vtd_dev_as; > } I fixed these up but pls take care, Clement. > -- > 2.49.0