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spf=pass smtp.mailfrom=benjamin.gaignard@collabora.com; dmarc=pass header.from= DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; t=1750427571; s=zohomail; d=collabora.com; i=benjamin.gaignard@collabora.com; h=Message-ID:Date:Date:MIME-Version:Subject:Subject:To:To:Cc:Cc:References:From:From:In-Reply-To:Content-Type:Content-Transfer-Encoding:Message-Id:Reply-To; bh=V459JMUmyF9w2CF7odfd6vdr2BDTmJkRuH7Scgg3lLo=; b=XMz83gLGVocBQQxhMXW3P41Im4nz6IP8qnRncCfexbBczpHYl1RS8MFGcilrvPYa gCE6lYBG8nfrS65sPW5tCrhl4mTSHQSVEhOyY6KOT13Ijf6FE/ha3v2o/A2qCdvvEkw 32AsJPhSZf6Hzk8n3E2138cANxh3Z8xrQfCPOdmQ= Received: by mx.zohomail.com with SMTPS id 1750427570159193.5196944847704; Fri, 20 Jun 2025 06:52:50 -0700 (PDT) Message-ID: Date: Fri, 20 Jun 2025 15:52:46 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v3 3/5] iommu: Add verisilicon IOMMU driver To: Jason Gunthorpe Cc: joro@8bytes.org, will@kernel.org, robin.murphy@arm.com, robh@kernel.org, krzk+dt@kernel.org, conor+dt@kernel.org, heiko@sntech.de, nicolas.dufresne@collabora.com, iommu@lists.linux.dev, devicetree@vger.kernel.org, linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-rockchip@lists.infradead.org, kernel@collabora.com References: <20250619131232.69208-1-benjamin.gaignard@collabora.com> <20250619131232.69208-4-benjamin.gaignard@collabora.com> <20250619134752.GB1643390@ziepe.ca> <073ffe14-d631-4a4f-8668-ddeb7d611448@collabora.com> <20250619165928.GA10257@ziepe.ca> <20250620120509.GA39770@ziepe.ca> Content-Language: en-US From: Benjamin Gaignard In-Reply-To: <20250620120509.GA39770@ziepe.ca> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20250620_145313_707601_F53AAE94 X-CRM114-Status: GOOD ( 36.81 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org Le 20/06/2025 à 14:05, Jason Gunthorpe a écrit : > On Fri, Jun 20, 2025 at 10:57:49AM +0200, Benjamin Gaignard wrote: >> Le 19/06/2025 à 18:59, Jason Gunthorpe a écrit : >>> On Thu, Jun 19, 2025 at 06:27:52PM +0200, Benjamin Gaignard wrote: >>>> Le 19/06/2025 à 15:47, Jason Gunthorpe a écrit : >>>>> Ugh. This ignores the gfp flags that are passed into map because you >>>>> have to force atomic due to the spinlock that shouldn't be there :( >>>>> This means it does not set GFP_KERNEL_ACCOUNT when required. It would >>>>> be better to continue to use the passed in GFP flags but override them >>>>> to atomic mode. >>>> I will add a gfp_t parameter and use it like that: >>>> page_table = iommu_alloc_pages_sz(gfp | GFP_ATOMIC | GFP_DMA32, SPAGE_SIZE); >>> This will or together GFP_ATOMIC and GFP_KERNEL, I don't think that >>> works.. >> I have test it, I don't see conflicts or errors. What worries you ? > Just looking at the bitmaps I'm not sure? Did you run with lockdep? Yes and it complains about that. I see that sun50i driver have more less the same struct than my driver but doesn't use lock. I will try see if I can remove the lock. >>>>>> +static int vsi_iommu_attach_device(struct iommu_domain *domain, >>>>>> + struct device *dev) >>>>>> +{ >>>>>> + struct vsi_iommu *iommu = dev_iommu_priv_get(dev); >>>>>> + struct vsi_iommu_domain *vsi_domain = to_vsi_domain(domain); >>>>>> + unsigned long flags; >>>>>> + int ret; >>>>>> + >>>>>> + if (WARN_ON(!iommu)) >>>>>> + return -ENODEV; >>>>>> + >>>>>> + /* iommu already attached */ >>>>>> + if (iommu->domain == domain) >>>>>> + return 0; >>>>>> + >>>>>> + ret = vsi_iommu_identity_attach(&vsi_identity_domain, dev); >>>>>> + if (ret) >>>>>> + return ret; >>>>> Hurm, this is actually quite bad, now that it is clear the HW is in an >>>>> identity mode it is actually a security problem for VFIO to switch the >>>>> translation to identity during attach_device. I'd really prefer new >>>>> drivers don't make this mistake. >>>>> >>>>> It seems the main thing motivating this is the fact a linked list has >>>>> only a single iommu->node so you can't attach the iommu to both the >>>>> new/old domain and atomically update the page table base. >>>>> >>>>> Is it possible for the HW to do a blocking behavior? That would be an >>>>> easy fix.. You should always be able to force this by allocating a >>>>> shared top page table level during probe time and making it entirely >>>>> empty while staying always in the paging mode. Maybe there is a less >>>>> expensive way. >>>>> >>>>> Otherwise you probably have work more like the other drivers and >>>>> allocate a struct for each attachment so you can have the iommu >>>>> attached two domains during the switch over and never drop to an >>>>> identity mode. >>>> I will remove the switch to identity domain and it will works fine. >>> You'll loose invalidations.. >>> >>> Maybe the easiest thing is to squish vsi_iommu_enable() and reorganize >>> it so that the spinlock is held across the register programming and >>> then you can atomically under the lock change the registers and change >>> the linked list. The register write cannot fail so this is fine. >>> >>> This should probably also flush the iotlb inside the lock. >> I will try to summarize: >> in vsi_iommu_attach_device() I should: >> - take the lock >> - do nothing if the domain is the same. >> - if iommu is used (ie powered up): >> - update the registers to enable the iommu >> - flush >> - update the link list >> - update iommu->domain >> - release the lock > That sounds believable, yes.. Though can you do the "powered up" checks > inside the spinlock - are they sleeping? Can they be done before the > spinlock? > >> in vsi_iommu_identity_attach() I should: >> - take the lock >> - do nothing if the domain is the same. >> - if iommu is used (ie powered up): >> - disable the iommu >> - remove the node from the list >> - update iommu->domain >> - release the lock > And maybe flush too? How does the caching hw work at this point? You > can't have stale entries in the cache when you switch back to an > enabled/translating configuration. So either the HW flushes implicitly > or you need to add a flush somewhere.. I do not have the documentation for the hardware but it seems that enable/disable are enough to do the job. > >> vsi_iommu_suspend() and vsi_iommu_resume() will also have to take the lock >> before calling vsi_iommu_disable() and vsi_iommu_enable(). > Yes, if they use iommu->domain that seems good > > If the above locking is a problem then I'd use the group mutex instead > during resume/suspend. The attach functions are already called with > the group mutex held. Does group mutex is also called when using vsi_iommu_map or vsi_iommu_unmap ? > >> Do I have to switch to identity domain in vsi_iommu_attach_device() >> before applying the requested domain ? > No, that is what creates the security problem. What you want is to > update the HW registers in a way that the HW just changes hitlessly > from one translation to another, then flush the cache. > > Jason