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Fri, 28 Feb 2020 06:43:11 -0800 (PST) Received: from myrica ([2001:171b:c9a8:fbc0:116c:c27a:3e7f:5eaf]) by smtp.gmail.com with ESMTPSA id t10sm12750189wru.59.2020.02.28.06.43.10 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 28 Feb 2020 06:43:11 -0800 (PST) Date: Fri, 28 Feb 2020 15:43:04 +0100 From: Jean-Philippe Brucker To: Jonathan Cameron Cc: iommu@lists.linux-foundation.org, devicetree@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-pci@vger.kernel.org, linux-mm@kvack.org, joro@8bytes.org, robh+dt@kernel.org, mark.rutland@arm.com, catalin.marinas@arm.com, will@kernel.org, robin.murphy@arm.com, kevin.tian@intel.com, baolu.lu@linux.intel.com, jacob.jun.pan@linux.intel.com, christian.koenig@amd.com, yi.l.liu@intel.com, zhangfei.gao@linaro.org, Jean-Philippe Brucker Subject: Re: [PATCH v4 02/26] iommu/sva: Manage process address spaces Message-ID: <20200228144304.GC2156@myrica> References: <20200224182401.353359-1-jean-philippe@linaro.org> <20200224182401.353359-3-jean-philippe@linaro.org> <20200226123506.000076fb@Huawei.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200226123506.000076fb@Huawei.com> X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Wed, Feb 26, 2020 at 12:35:06PM +0000, Jonathan Cameron wrote: > > + * A single Process Address Space ID (PASID) is allocated for each mm. In the > > + * example, devices use PASID 1 to read/write into address space X and PASID 2 > > + * to read/write into address space Y. Calling iommu_sva_get_pasid() on bond 1 > > + * returns 1, and calling it on bonds 2-4 returns 2. > > + * > > + * Hardware tables describing this configuration in the IOMMU would typically > > + * look like this: > > + * > > + * PASID tables > > + * of domain A > > + * .->+--------+ > > + * / 0 | |-------> io_pgtable > > + * / +--------+ > > + * Device tables / 1 | |-------> pgd X > > + * +--------+ / +--------+ > > + * 00:00.0 | A |-' 2 | |--. > > + * +--------+ +--------+ \ > > + * : : 3 | | \ > > + * +--------+ +--------+ --> pgd Y > > + * 00:01.0 | B |--. / > > + * +--------+ \ | > > + * 00:01.1 | B |----+ PASID tables | > > + * +--------+ \ of domain B | > > + * '->+--------+ | > > + * 0 | |-- | --> io_pgtable > > + * +--------+ | > > + * 1 | | | > > + * +--------+ | > > + * 2 | |---' > > + * +--------+ > > + * 3 | | > > + * +--------+ > > + * > > + * With this model, a single call binds all devices in a given domain to an > > + * address space. Other devices in the domain will get the same bond implicitly. > > + * However, users must issue one bind() for each device, because IOMMUs may > > + * implement SVA differently. Furthermore, mandating one bind() per device > > + * allows the driver to perform sanity-checks on device capabilities. > > > + * > > + * In some IOMMUs, one entry of the PASID table (typically the first one) can > > + * hold non-PASID translations. In this case PASID 0 is reserved and the first > > + * entry points to the io_pgtable pointer. In other IOMMUs the io_pgtable > > + * pointer is held in the device table and PASID 0 is available to the > > + * allocator. > > Is it worth hammering home in here that we can only do this because the PASID space > is global (with exception of PASID 0)? It's a convenient simplification but not > necessarily a hardware restriction so perhaps we should remind people somewhere in here? I could add this four paragraphs up: "A single Process Address Space ID (PASID) is allocated for each mm. It is a choice made for the Linux SVA implementation, not a hardware restriction." > > + */ > > + > > +struct io_mm { > > + struct list_head devices; > > + struct mm_struct *mm; > > + struct mmu_notifier notifier; > > + > > + /* Late initialization */ > > + const struct io_mm_ops *ops; > > + void *ctx; > > + int pasid; > > +}; > > + > > +#define to_io_mm(mmu_notifier) container_of(mmu_notifier, struct io_mm, notifier) > > +#define to_iommu_bond(handle) container_of(handle, struct iommu_bond, sva) > > Code ordering wise, do we want this after the definition of iommu_bond? > > For both of these it's a bit non obvious what they come 'from'. > I wouldn't naturally assume to_io_mm gets me from notifier to the io_mm > for example. Not sure it matters though if these are only used in a few > places. Right, I can rename the first one to mn_to_io_mm(). The second one I think might be good enough. > > +static struct iommu_sva * > > +io_mm_attach(struct device *dev, struct io_mm *io_mm, void *drvdata) > > +{ > > + int ret = 0; > > I'm fairly sure this is set in all paths below. Now, of course the > compiler might not think that in which case fair enough :) > > > + bool attach_domain = true; > > + struct iommu_bond *bond, *tmp; > > + struct iommu_domain *domain, *other; > > + struct iommu_sva_param *param = dev->iommu_param->sva_param; > > + > > + domain = iommu_get_domain_for_dev(dev); > > + > > + bond = kzalloc(sizeof(*bond), GFP_KERNEL); > > + if (!bond) > > + return ERR_PTR(-ENOMEM); > > + > > + bond->sva.dev = dev; > > + bond->drvdata = drvdata; > > + refcount_set(&bond->refs, 1); > > + RCU_INIT_POINTER(bond->io_mm, io_mm); > > + > > + mutex_lock(&iommu_sva_lock); > > + /* Is it already bound to the device or domain? */ > > + list_for_each_entry(tmp, &io_mm->devices, mm_head) { > > + if (tmp->sva.dev != dev) { > > + other = iommu_get_domain_for_dev(tmp->sva.dev); > > + if (domain == other) > > + attach_domain = false; > > + > > + continue; > > + } > > + > > + if (WARN_ON(tmp->drvdata != drvdata)) { > > + ret = -EINVAL; > > + goto err_free; > > + } > > + > > + /* > > + * Hold a single io_mm reference per bond. Note that we can't > > + * return an error after this, otherwise the caller would drop > > + * an additional reference to the io_mm. > > + */ > > + refcount_inc(&tmp->refs); > > + io_mm_put(io_mm); > > + kfree(bond); > > Free outside the lock would be ever so slightly more logical given we allocated > before taking the lock. > > > + mutex_unlock(&iommu_sva_lock); > > + return &tmp->sva; > > + } > > + > > + list_add_rcu(&bond->mm_head, &io_mm->devices); > > + param->nr_bonds++; > > + mutex_unlock(&iommu_sva_lock); > > + > > + ret = io_mm->ops->attach(bond->sva.dev, io_mm->pasid, io_mm->ctx, > > + attach_domain); > > + if (ret) > > + goto err_remove; > > + > > + return &bond->sva; > > + > > +err_remove: > > + /* > > + * At this point concurrent threads may have started to access the > > + * io_mm->devices list in order to invalidate address ranges, which > > + * requires to free the bond via kfree_rcu() > > + */ > > + mutex_lock(&iommu_sva_lock); > > + param->nr_bonds--; > > + list_del_rcu(&bond->mm_head); > > + > > +err_free: > > + mutex_unlock(&iommu_sva_lock); > > + kfree_rcu(bond, rcu_head); > > I don't suppose it matters really but we don't need the rcu free if > we follow the err_free goto. Perhaps we are cleaner in this case > to not use a unified exit path but do that case inline? Agreed, though I moved the kzalloc() later as suggested by Jacob, I think it looks a little better and simplifies the error paths Thanks, Jean