From 82582f85ed22ba6cd27fea76b4248745f3b9fdf7 Mon Sep 17 00:00:00 2001 From: Suravee Suthikulpanit Date: Mon, 18 Nov 2024 05:49:30 +0000 Subject: [PATCH] iommu/amd: Disable AMD IOMMU if CMPXCHG16B feature is not supported According to the AMD IOMMU spec, IOMMU hardware reads the entire DTE in a single 256-bit transaction. It is recommended to update DTE using 128-bit operation followed by an INVALIDATE_DEVTAB_ENTYRY command when the IV=1b or V=1b before the change. According to the AMD BIOS and Kernel Developer's Guide (BDKG) dated back to family 10h Processor [1], which is the first introduction of AMD IOMMU, AMD processor always has CPUID Fn0000_0001_ECX[CMPXCHG16B]=1. Therefore, it is safe to assume cmpxchg128 is available with all AMD processor w/ IOMMU. In addition, the CMPXCHG16B feature has already been checked separately before enabling the GA, XT, and GAM modes. Consolidate the detection logic, and fail the IOMMU initialization if the feature is not supported. [1] https://www.amd.com/content/dam/amd/en/documents/archived-tech-docs/programmer-references/31116.pdf Reviewed-by: Jason Gunthorpe Suggested-by: Jason Gunthorpe Signed-off-by: Suravee Suthikulpanit Link: https://lore.kernel.org/r/20241118054937.5203-3-suravee.suthikulpanit@amd.com Signed-off-by: Joerg Roedel --- drivers/iommu/amd/init.c | 23 +++++++++-------------- 1 file changed, 9 insertions(+), 14 deletions(-) diff --git a/drivers/iommu/amd/init.c b/drivers/iommu/amd/init.c index 3a7b2b0472fa..c1607b29ebf4 100644 --- a/drivers/iommu/amd/init.c +++ b/drivers/iommu/amd/init.c @@ -1752,13 +1752,8 @@ static int __init init_iommu_one(struct amd_iommu *iommu, struct ivhd_header *h, else iommu->mmio_phys_end = MMIO_CNTR_CONF_OFFSET; - /* - * Note: GA (128-bit IRTE) mode requires cmpxchg16b supports. - * GAM also requires GA mode. Therefore, we need to - * check cmpxchg16b support before enabling it. - */ - if (!boot_cpu_has(X86_FEATURE_CX16) || - ((h->efr_attr & (0x1 << IOMMU_FEAT_GASUP_SHIFT)) == 0)) + /* GAM requires GA mode. */ + if ((h->efr_attr & (0x1 << IOMMU_FEAT_GASUP_SHIFT)) == 0) amd_iommu_guest_ir = AMD_IOMMU_GUEST_IR_LEGACY; break; case 0x11: @@ -1768,13 +1763,8 @@ static int __init init_iommu_one(struct amd_iommu *iommu, struct ivhd_header *h, else iommu->mmio_phys_end = MMIO_CNTR_CONF_OFFSET; - /* - * Note: GA (128-bit IRTE) mode requires cmpxchg16b supports. - * XT, GAM also requires GA mode. Therefore, we need to - * check cmpxchg16b support before enabling them. - */ - if (!boot_cpu_has(X86_FEATURE_CX16) || - ((h->efr_reg & (0x1 << IOMMU_EFR_GASUP_SHIFT)) == 0)) { + /* XT and GAM require GA mode. */ + if ((h->efr_reg & (0x1 << IOMMU_EFR_GASUP_SHIFT)) == 0) { amd_iommu_guest_ir = AMD_IOMMU_GUEST_IR_LEGACY; break; } @@ -3028,6 +3018,11 @@ static int __init early_amd_iommu_init(void) return -EINVAL; } + if (!boot_cpu_has(X86_FEATURE_CX16)) { + pr_err("Failed to initialize. The CMPXCHG16B feature is required.\n"); + return -EINVAL; + } + /* * Validate checksum here so we don't need to do it when * we actually parse the table