From 2636fcdc15c707d5e097770133f0afb69e8d70c9 Mon Sep 17 00:00:00 2001 From: Teddy Astie Date: Fri, 24 Jan 2025 12:31:15 +0100 Subject: [PATCH] x86/iommu: check for CMPXCHG16B when enabling IOMMU MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit All hardware with VT-d/AMD-Vi has CMPXCHG16B support. Check this at initialisation time, and otherwise refuse to use the IOMMU. If the local APICs support x2APIC mode the IOMMU support for interrupt remapping will be checked earlier using a specific helper. If no support for CX16 is detected by that earlier hook disable the IOMMU at that point and prevent further poking for CX16 later in the boot process, which would also fail. There's a possible corner case when running virtualized, and the underlying hypervisor exposing an IOMMU but no CMPXCHG16B support. In which case ignoring the IOMMU is fine, albeit the most natural would be for the underlying hypervisor to also expose CMPXCHG16B support if an IOMMU is available to the VM. Note this change only introduces the checks, but doesn't remove the now stale checks for CX16 support sprinkled in the IOMMU code. Further changes will take care of that. Suggested-by: Andrew Cooper Signed-off-by: Teddy Astie Signed-off-by: Roger Pau Monné Reviewed-by: Andrew Cooper Release-Acked-by: Oleksii Kurochko --- xen/drivers/passthrough/amd/iommu_intr.c | 13 +++++++++++++ xen/drivers/passthrough/amd/pci_amd_iommu.c | 6 ++++++ xen/drivers/passthrough/vtd/intremap.c | 13 +++++++++++++ xen/drivers/passthrough/vtd/iommu.c | 7 +++++++ 4 files changed, 39 insertions(+) diff --git a/xen/drivers/passthrough/amd/iommu_intr.c b/xen/drivers/passthrough/amd/iommu_intr.c index 7fc796dec2..f07fd9e3d9 100644 --- a/xen/drivers/passthrough/amd/iommu_intr.c +++ b/xen/drivers/passthrough/amd/iommu_intr.c @@ -649,6 +649,19 @@ bool __init cf_check iov_supports_xt(void) if ( !iommu_enable || !iommu_intremap ) return false; + if ( unlikely(!cpu_has_cx16) ) + { + AMD_IOMMU_ERROR("no CMPXCHG16B support, disabling IOMMU\n"); + /* + * Disable IOMMU support at once: there's no reason to check for CX16 + * yet again when attempting to initialize IOMMU DMA remapping + * functionality or interrupt remapping without x2APIC support. + */ + iommu_enable = false; + iommu_intremap = iommu_intremap_off; + return false; + } + if ( amd_iommu_prepare(true) ) return false; diff --git a/xen/drivers/passthrough/amd/pci_amd_iommu.c b/xen/drivers/passthrough/amd/pci_amd_iommu.c index 73dcc4a2dd..f96f59440b 100644 --- a/xen/drivers/passthrough/amd/pci_amd_iommu.c +++ b/xen/drivers/passthrough/amd/pci_amd_iommu.c @@ -309,6 +309,12 @@ static int __init cf_check iov_detect(void) if ( !iommu_enable && !iommu_intremap ) return 0; + if ( unlikely(!cpu_has_cx16) ) + { + AMD_IOMMU_ERROR("no CMPXCHG16B support, disabling IOMMU\n"); + return -ENODEV; + } + if ( (init_done ? amd_iommu_init_late() : amd_iommu_init(false)) != 0 ) { diff --git a/xen/drivers/passthrough/vtd/intremap.c b/xen/drivers/passthrough/vtd/intremap.c index c504852eb8..233db5cb64 100644 --- a/xen/drivers/passthrough/vtd/intremap.c +++ b/xen/drivers/passthrough/vtd/intremap.c @@ -150,6 +150,19 @@ bool __init cf_check intel_iommu_supports_eim(void) if ( !iommu_qinval || !iommu_intremap || list_empty(&acpi_drhd_units) ) return false; + if ( unlikely(!cpu_has_cx16) ) + { + printk(XENLOG_ERR VTDPREFIX "no CMPXCHG16B support, disabling IOMMU\n"); + /* + * Disable IOMMU support at once: there's no reason to check for CX16 + * yet again when attempting to initialize IOMMU DMA remapping + * functionality or interrupt remapping without x2APIC support. + */ + iommu_enable = false; + iommu_intremap = iommu_intremap_off; + return false; + } + /* We MUST have a DRHD unit for each IOAPIC. */ for ( apic = 0; apic < nr_ioapics; apic++ ) if ( !ioapic_to_drhd(IO_APIC_ID(apic)) ) diff --git a/xen/drivers/passthrough/vtd/iommu.c b/xen/drivers/passthrough/vtd/iommu.c index 27a4d16401..3daedc4f55 100644 --- a/xen/drivers/passthrough/vtd/iommu.c +++ b/xen/drivers/passthrough/vtd/iommu.c @@ -2633,6 +2633,13 @@ static int __init cf_check vtd_setup(void) int ret; bool reg_inval_supported = true; + if ( unlikely(!cpu_has_cx16) ) + { + printk(XENLOG_ERR VTDPREFIX "no CMPXCHG16B support, disabling IOMMU\n"); + ret = -ENODEV; + goto error; + } + if ( list_empty(&acpi_drhd_units) ) { ret = -ENODEV;