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Wed, 16 Sep 2026 11:44:54 -0700 From: To: , , , , , , , , , , , , , , , CC: , , , , , , Subject: [PATCH v2 04/10] hw/vfio/pci: Enforce the passthrough topology for a CXL device Date: Thu, 17 Sep 2026 00:14:06 +0530 Message-ID: <20260916184412.3825713-5-mhonap@nvidia.com> X-Mailer: git-send-email 2.25.1 In-Reply-To: <20260916184412.3825713-1-mhonap@nvidia.com> References: <20260916184412.3825713-1-mhonap@nvidia.com> Precedence: bulk X-Mailing-List: linux-cxl@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Content-Type: text/plain X-ClientProxiedBy: rnnvmail202.nvidia.com (10.129.68.7) To rnnvmail202.nvidia.com (10.129.68.7) X-EOPAttributedMessage: 0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: SJ1PEPF00002310:EE_|BY5PR12MB4289:EE_ X-MS-Office365-Filtering-Correlation-Id: bac5a289-d116-49e4-cb87-08df1422ad41 X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|376014|23010399003|36860700016|82310400026|7416014|1800799024|921020|11063799006|56012099006|10067099003|22082099003|18002099003; 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the decoders above it are covered only while the pxb-cxl host bridge stays in passthrough mode. Reject a switch in the path, or a host bridge taken out of passthrough, at realize before any mapping exists. AI-used-for: code (prototype) Signed-off-by: Manish Honap --- hw/vfio/pci.c | 73 +++++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 73 insertions(+) diff --git a/hw/vfio/pci.c b/hw/vfio/pci.c index 2f84af5cf8..10b13f200d 100644 --- a/hw/vfio/pci.c +++ b/hw/vfio/pci.c @@ -27,6 +27,7 @@ #include "hw/pci/msi.h" #include "hw/pci/msix.h" #include "hw/pci/pci_bridge.h" +#include "hw/cxl/cxl.h" #include "hw/core/qdev-properties.h" #include "hw/core/qdev-properties-system.h" #include "hw/vfio/vfio-cpr.h" @@ -3570,6 +3571,73 @@ bool vfio_pci_interrupt_setup(VFIOPCIDevice *vdev, Error **errp) return true; } +/* + * Walk the endpoint's ancestor bridges up to its pxb-cxl host bridge. A CXL + * switch in the path is rejected: the guest would then have to program switch + * decoders, which the passthrough model does not yet cover. This is the single + * place the supported-topology assumption lives, so switch support later + * relaxes it here. + */ +static PXBCXLDev *vfio_cxl_find_pxb(VFIOPCIDevice *vdev, Error **errp) +{ + PCIBus *bus = pci_get_bus(&vdev->parent_obj); + + if (!object_dynamic_cast(OBJECT(bus), TYPE_CXL_BUS)) { + error_setg(errp, + "vfio-cxl: %s: endpoint is not on a CXL root port (cxl-rp)", + vdev->vbasedev.name); + return NULL; + } + + for (; bus; ) { + PCIDevice *bridge = bus->parent_dev; + + if (!bridge) { + break; + } + if (object_dynamic_cast(OBJECT(bridge), TYPE_CXL_USP) || + object_dynamic_cast(OBJECT(bridge), TYPE_CXL_DSP)) { + error_setg(errp, + "vfio-cxl: %s: switch-attached topology not supported", + vdev->vbasedev.name); + return NULL; + } + if (object_dynamic_cast(OBJECT(bridge), TYPE_PXB_CXL_DEV)) { + return PXB_CXL_DEV(bridge); + } + if (pci_bus_is_root(bus)) { + break; + } + bus = pci_get_bus(bridge); + } + + error_setg(errp, "vfio-cxl: %s: not attached below a pxb-cxl host bridge", + vdev->vbasedev.name); + return NULL; +} + +/* + * Only guest's endpoint decoder is programmed, so the host bridge must stay in + * HDM passthrough mode. Reject anything else at realize, before a mapping is + * built. cxl_get_hb_passthrough() reflects reset state and is not + * settled yet here, so gate on the static hdm_for_passthrough property. + */ +static bool vfio_cxl_check_topology(VFIOPCIDevice *vdev, Error **errp) +{ + PXBCXLDev *pxb = vfio_cxl_find_pxb(vdev, errp); + + if (!pxb) { + return false; + } + if (pxb->hdm_for_passthrough) { + error_setg(errp, + "vfio-cxl: %s: the pxb-cxl must be in HDM passthrough mode " + "(do not set hdm_for_passthrough)", vdev->vbasedev.name); + return false; + } + return true; +} + /* * Learn the CXL geometry the kernel reports: the HPA-backed HDM memory region * and the trapped HDM decoder block (which BAR carries it and at what offset). @@ -3623,6 +3691,11 @@ static bool vfio_cxl_setup(VFIOPCIDevice *vdev, Error **errp) cxl->dpa_size = mem_info->size; cxl->comp_bar = cap->bar; cxl->hdm_offset = cap->offset; + + if (!vfio_cxl_check_topology(vdev, errp)) { + return false; + } + cxl->enabled = true; return true; -- 2.25.1