From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from linux.microsoft.com (linux.microsoft.com [13.77.154.182]) by smtp.subspace.kernel.org (Postfix) with ESMTP id 90E723BE627; Wed, 8 Jul 2026 10:33:18 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=13.77.154.182 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1783506806; cv=none; b=G800AtFPRxlBnonKMHLGlX08zoBrRcCTubW7Uyae0DKMh3IwDVfenBYn6/JRTD/WcmpkTqfWGgCzpzbtq1sk222PXDhvLUlGoc2Abi4EA2Ne8N6JRcbuQrQz5iUxxndUKzRRoqmwtHwU+jqRRkNo4wEzbnyGRerm6jipDLf9idw= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1783506806; c=relaxed/simple; bh=KOfxWwqthP89d883QEsbCbM2ovIyad53dh00YEqUADw=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=WlFyHdQ1Jw5DjlkfRUpEGipa+WBUud/xcMej2nGfQqC3gwETkmUmkG+rliH1nb6YlFUVwd7M9hvCODu/Qjaj76dIaemEib/wJgRxcx/Bhcd2InfIDC+zjMknUp8rXzVrgo8cFm0FP4Z7Lljz1gE92qUPPiA5341lThQ32Tntg7U= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.microsoft.com; spf=pass smtp.mailfrom=linux.microsoft.com; dkim=pass (1024-bit key) header.d=linux.microsoft.com header.i=@linux.microsoft.com header.b=Sr78UQcR; arc=none smtp.client-ip=13.77.154.182 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.microsoft.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linux.microsoft.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux.microsoft.com header.i=@linux.microsoft.com header.b="Sr78UQcR" Received: from localhost (unknown [167.220.233.38]) by linux.microsoft.com (Postfix) with ESMTPSA id D5C4D20B7166; Wed, 8 Jul 2026 03:33:07 -0700 (PDT) DKIM-Filter: OpenDKIM Filter v2.11.0 linux.microsoft.com D5C4D20B7166 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.microsoft.com; s=default; t=1783506788; bh=vKK52gM9w8/zMLU0AJulU3rrns4vwDO+QxLbjmC5IBM=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=Sr78UQcRnCYTn1/xwmJMo2d+1aFNNywFHRhXQCDH0X+7etsiUg54EDSsmazCGRL5i jgqLm8vhzXMzQhIHs0MX+01zUIOGdVHjAVVLUP+/qXRlSfRwZAxJ2qfm493XAGxNBO mDMoAhmWQw21//CwGcbOlUJqy4FdpFIEtS2QHAYE= Date: Wed, 8 Jul 2026 18:33:10 +0800 From: Yu Zhang To: Jason Gunthorpe Cc: linux-kernel@vger.kernel.org, linux-hyperv@vger.kernel.org, iommu@lists.linux.dev, linux-pci@vger.kernel.org, linux-arch@vger.kernel.org, wei.liu@kernel.org, kys@microsoft.com, haiyangz@microsoft.com, decui@microsoft.com, longli@microsoft.com, joro@8bytes.org, will@kernel.org, robin.murphy@arm.com, bhelgaas@google.com, kwilczynski@kernel.org, lpieralisi@kernel.org, mani@kernel.org, robh@kernel.org, arnd@arndb.de, mhklinux@outlook.com, jacob.pan@linux.microsoft.com, tgopinath@linux.microsoft.com, easwar.hariharan@linux.microsoft.com, mrathor@linux.microsoft.com Subject: Re: [PATCH v2 3/4] iommu/hyperv: Add para-virtualized IOMMU support for Hyper-V guest Message-ID: References: <20260702160518.311234-1-zhangyu1@linux.microsoft.com> <20260702160518.311234-4-zhangyu1@linux.microsoft.com> <20260703173248.GB1968184@ziepe.ca> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260703173248.GB1968184@ziepe.ca> On Fri, Jul 03, 2026 at 02:32:48PM -0300, Jason Gunthorpe wrote: > On Fri, Jul 03, 2026 at 12:05:17AM +0800, Yu Zhang wrote: > > > +static bool hv_iommu_capable(struct device *dev, enum iommu_cap cap) > > +{ > > + switch (cap) { > > + case IOMMU_CAP_CACHE_COHERENCY: > > + return true; > > + case IOMMU_CAP_DEFERRED_FLUSH: > > + return true; > > This CAP isn't necessary anymore > Right, thanks for pointing this out! > > +static struct iommu_device *hv_iommu_probe_device(struct device *dev) > > +{ > > + struct pci_dev *pdev; > > + struct hv_iommu_endpoint *vdev; > > + struct hv_output_get_logical_device_property device_iommu_property = {0}; > > + > > + if (!dev_is_pci(dev)) > > + return ERR_PTR(-ENODEV); > > + > > + pdev = to_pci_dev(dev); > > + > > + if (hv_iommu_get_logical_device_property(dev, > > + HV_LOGICAL_DEVICE_PROPERTY_PVIOMMU, > > + &device_iommu_property) || > > + !(device_iommu_property.device_iommu & HV_DEVICE_IOMMU_ENABLED)) > > + return ERR_PTR(-ENODEV); > > + > > + vdev = kzalloc_obj(*vdev, GFP_KERNEL); > > + if (!vdev) > > + return ERR_PTR(-ENOMEM); > > + > > + vdev->dev = dev; > > + vdev->hv_iommu = hv_iommu_device; > > + dev_iommu_priv_set(dev, vdev); > > + > > + if (hv_iommu_ats_supported(hv_iommu_device->cap) && > > + pci_ats_supported(pdev)) > > + pci_enable_ats(pdev, __ffs(hv_iommu_device->pgsize_bitmap)); > > This can probably just be PAGE_SHIFT Indeed. > > Also ATS shouldn't be enabled until a translation is installed, > otherwise the driver cannot participate in the ATS error handling > Nicolin is working on. > Yes.I'll move ATS enablement into a paging-domain-specific attach wrapper that calls pci_enable_ats(pdev, PAGE_SHIFT) after the attach hypercall succeeds. And maybe blocking attach shall also call pci_disable_ats() before the hypercall to prevent stale ATC entries from bypassing the block? Something like: static int hv_iommu_paging_attach_dev(...) { ret = hv_iommu_attach_dev(domain, dev, old); if (ret) return ret; if (!pdev->ats_enabled && ats_supported) pci_enable_ats(pdev, PAGE_SHIFT); return 0; } static int hv_iommu_blocking_attach_dev(...) { if (pdev->ats_enabled) pci_disable_ats(pdev); ret = hv_iommu_attach_dev(domain, dev, old); ... } Does this look right? > > +static void hv_iommu_release_device(struct device *dev) > > +{ > > + struct hv_iommu_endpoint *vdev = dev_iommu_priv_get(dev); > > + struct pci_dev *pdev = to_pci_dev(dev); > > + > > + if (pdev->ats_enabled) > > + pci_disable_ats(pdev); > > + > > + dev_iommu_priv_set(dev, NULL); > > No necessary, the caller does it > Yes. Thanks! > > +static struct iommu_group *hv_iommu_device_group(struct device *dev) > > +{ > > + if (dev_is_pci(dev)) > > + return pci_device_group(dev); > > + > > + WARN_ON_ONCE(1); > > + return generic_device_group(dev); > > I think you can just return failure here instead of WARN_ON ? > Yes, will change to return ERR_PTR(-ENODEV). > > +static int __init hv_initialize_static_domains(void) > > +{ > > + int ret; > > + struct hv_iommu_domain *hv_domain; > > + > > + /* Default stage-1 identity domain */ > > + hv_domain = &hv_identity_domain; > > + > > + ret = hv_create_device_domain(hv_domain, HV_DEVICE_DOMAIN_TYPE_S1); > > + if (ret) > > + return ret; > > + > > + ret = hv_configure_device_domain(hv_domain, IOMMU_DOMAIN_IDENTITY); > > + if (ret) > > + goto delete_identity_domain; > > IMHO I would change this around to have a single function that accepts > a struct hv_input_configure_device_domain as input and does both of > the hypercalls inside. Then here it is easy to directly construct the > hv_input_configure_device_domain for blocking and identity. > > I'd be happy if this never touched domain_type, drivers shouldn't be > touching that. > Good idea. Maybe we can just change hv_configure_device_domain() to take a "struct hv_device_domain_settings *" directly - that way each caller constructs the HW settings explicitly and domain_type is not needed at all. Does that sound right? > > +static void __init hv_init_iommu_device(struct hv_iommu_dev *hv_iommu, > > + struct hv_output_get_iommu_capabilities *hv_iommu_cap) > > +{ > > + ida_init(&hv_iommu->domain_ids); > > + > > + hv_iommu->cap = hv_iommu_cap->iommu_cap; > > + hv_iommu->max_iova_width = hv_iommu_cap->max_iova_width; > > + if (!hv_iommu_5lvl_supported(hv_iommu->cap) && > > + hv_iommu->max_iova_width > 48) { > > + pr_info("5-level paging not supported, limiting iova width to 48.\n"); > > + hv_iommu->max_iova_width = 48; > > + } > > + > > + hv_iommu->geometry = (struct iommu_domain_geometry) { > > + .aperture_start = 0, > > + .aperture_end = (((u64)1) << hv_iommu->max_iova_width) - 1, > > + .force_aperture = true, > > + }; > > I don't see anything reading this, I don't expect this to be used? > > The max_iova_width has to be passed into the iommupt creation, which > it does: > > + cfg.common.hw_max_vasz_lg2 = hv_iommu_device->max_iova_width; > + cfg.common.hw_max_oasz_lg2 = 52; > + cfg.top_level = (hv_iommu_device->max_iova_width > 48) ? 4 : 3; > + ret = pt_iommu_x86_64_init(&hv_domain->pt_iommu_x86_64, &cfg, GFP_KERNEL); > + if (ret) > > So just delete hv->iommu->geometry. > Right. Will remove. > Also, VT-D has weirdness where the HW can require a 4 level table but > only a 3 level worth of IOVA width is being used. This was a > real-world bug we hit when converting to iommupt. This interaction > with the HV doesn't seem able to represent that. > Is this the issue fixed by commit d856f9d27885 ("iommupt/vtd: Allow VT-d to have a larger table top than the vasz requires")? For pvIOMMU the first-stage table is either 4-level (max_iova_width <= 48) or 5-level (max_iova_width > 48 && 5lvl cap set). Is there a scenario where this would still be a problem? > > + /* > > + * The page table code only maps x86 page sizes (4K/2M/1G); require the > > + * hypervisor to advertise a non-empty subset of exactly those. > > + */ > > + if (!hv_iommu_cap.pgsize_bitmap || > > + (hv_iommu_cap.pgsize_bitmap & ~(u64)(SZ_4K | SZ_2M | SZ_1G))) { > > + pr_err("unsupported page sizes: pgsize_bitmap=0x%llx\n", > > + hv_iommu_cap.pgsize_bitmap); > > + return -ENODEV; > > + } > > This can just be > > if (!(hv_iommu_cap.pgsize_bitmap & PAGE_SHIFT)) { > pr_err("unsupported page sizes: pgsize_bitmap=0x%llx\n", > hv_iommu_cap.pgsize_bitmap); > } return -ENODEV; > > Which is all you really need. If the HV doesn't support 1G it is > perfectly fine, the iommupt page bitmap is already masked by this. > Good point, it's much simpler. And I assume you meant PAGE_SIZE / SZ_4K instead of PAGE_SHIFT here. :) > > + ret = iommu_device_register(&hv_iommu->iommu, &hv_iommu_ops, NULL); > > + if (ret) { > > + pr_err("iommu_device_register failed: %d\n", ret); > > + goto err_sysfs_remove; > > + } > > + > > + pr_info("successfully initialized\n"); > > Don't log someting so vauge? > With pr_fmt defined as "Hyper-V pvIOMMU: ", this shows up as "Hyper-V pvIOMMU: successfully initialized" in dmesg. I'd like to keep some indication that pvIOMMU init succeeded at boot. Is this still too vague? Would it be better if I also print capabilities like IOVA width and supported page sizes here? Thanks! B.R. Yu > Jason >