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X-OriginatorOrg: amd.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 25 Aug 2025 21:46:11.4318 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: 02cff8d8-ebbb-4b6b-3247-08dde420ceb8 X-MS-Exchange-CrossTenant-Id: 3dd8961f-e488-4e60-8e11-a82d994e183d X-MS-Exchange-CrossTenant-OriginalAttributedTenantConnectingIp: TenantId=3dd8961f-e488-4e60-8e11-a82d994e183d;Ip=[165.204.84.17];Helo=[SATLEXMB04.amd.com] X-MS-Exchange-CrossTenant-AuthSource: BN3PEPF0000B374.namprd21.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Anonymous X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem X-MS-Exchange-Transport-CrossTenantHeadersStamped: CH1PR12MB9693 From: Ashish Kalra After a panic if SNP is enabled in the previous kernel then the kdump kernel boots with IOMMU SNP enforcement still enabled. IOMMU completion wait buffers (CWBs), command buffers and event buffer registers remain locked and exclusive to the previous kernel. Attempts to allocate and use new buffers in the kdump kernel fail, as hardware ignores writes to the locked MMIO registers as per AMD IOMMU spec Section 2.12.2.1. This results in repeated "Completion-Wait loop timed out" errors and a second kernel panic: "Kernel panic - not syncing: timer doesn't work through Interrupt-remapped IO-APIC" The list of MMIO registers locked and which ignore writes after failed SNP shutdown are mentioned in the AMD IOMMU specifications below: Section 2.12.2.1. https://docs.amd.com/v/u/en-US/48882_3.10_PUB Reuse the pages of the previous kernel for completion wait buffers, command buffers, event buffers and memremap them during kdump boot and essentially work with an already enabled IOMMU configuration and re-using the previous kernel=E2=80=99s data structures. Reusing of command buffers and event buffers is now done for kdump boot irrespective of SNP being enabled during kdump. Re-use of completion wait buffers is only done when SNP is enabled as the exclusion base register is used for the completion wait buffer (CWB) address only when SNP is enabled. Reviewed-by: Vasant Hegde Tested-by: Sairaj Kodilkar Signed-off-by: Ashish Kalra --- drivers/iommu/amd/amd_iommu_types.h | 5 + drivers/iommu/amd/init.c | 152 +++++++++++++++++++++++++--- drivers/iommu/amd/iommu.c | 2 +- 3 files changed, 146 insertions(+), 13 deletions(-) diff --git a/drivers/iommu/amd/amd_iommu_types.h b/drivers/iommu/amd/amd_io= mmu_types.h index 5219d7ddfdaa..8a863cae99db 100644 --- a/drivers/iommu/amd/amd_iommu_types.h +++ b/drivers/iommu/amd/amd_iommu_types.h @@ -791,6 +791,11 @@ struct amd_iommu { u32 flags; volatile u64 *cmd_sem; atomic64_t cmd_sem_val; + /* + * Track physical address to directly use it in build_completion_wait() + * and avoid adding any special checks and handling for kdump. + */ + u64 cmd_sem_paddr; =20 #ifdef CONFIG_AMD_IOMMU_DEBUGFS /* DebugFS Info */ diff --git a/drivers/iommu/amd/init.c b/drivers/iommu/amd/init.c index 8de689b2c5ed..5b8e9d6befa5 100644 --- a/drivers/iommu/amd/init.c +++ b/drivers/iommu/amd/init.c @@ -710,6 +710,26 @@ static void __init free_alias_table(struct amd_iommu_p= ci_seg *pci_seg) pci_seg->alias_table =3D NULL; } =20 +static inline void *iommu_memremap(unsigned long paddr, size_t size) +{ + phys_addr_t phys; + + if (!paddr) + return NULL; + + /* + * Obtain true physical address in kdump kernel when SME is enabled. + * Currently, previous kernel with SME enabled and kdump kernel + * with SME support disabled is not supported. + */ + phys =3D __sme_clr(paddr); + + if (cc_platform_has(CC_ATTR_HOST_MEM_ENCRYPT)) + return (__force void *)ioremap_encrypted(phys, size); + else + return memremap(phys, size, MEMREMAP_WB); +} + /* * Allocates the command buffer. This buffer is per AMD IOMMU. We can * write commands to that buffer later and the IOMMU will execute them @@ -942,8 +962,91 @@ static int iommu_init_ga_log(struct amd_iommu *iommu) static int __init alloc_cwwb_sem(struct amd_iommu *iommu) { iommu->cmd_sem =3D iommu_alloc_4k_pages(iommu, GFP_KERNEL, 1); + if (!iommu->cmd_sem) + return -ENOMEM; + iommu->cmd_sem_paddr =3D iommu_virt_to_phys((void *)iommu->cmd_sem); + return 0; +} + +static int __init remap_event_buffer(struct amd_iommu *iommu) +{ + u64 paddr; + + pr_info_once("Re-using event buffer from the previous kernel\n"); + paddr =3D readq(iommu->mmio_base + MMIO_EVT_BUF_OFFSET) & PM_ADDR_MASK; + iommu->evt_buf =3D iommu_memremap(paddr, EVT_BUFFER_SIZE); + + return iommu->evt_buf ? 0 : -ENOMEM; +} + +static int __init remap_command_buffer(struct amd_iommu *iommu) +{ + u64 paddr; =20 - return iommu->cmd_sem ? 0 : -ENOMEM; + pr_info_once("Re-using command buffer from the previous kernel\n"); + paddr =3D readq(iommu->mmio_base + MMIO_CMD_BUF_OFFSET) & PM_ADDR_MASK; + iommu->cmd_buf =3D iommu_memremap(paddr, CMD_BUFFER_SIZE); + + return iommu->cmd_buf ? 0 : -ENOMEM; +} + +static int __init remap_or_alloc_cwwb_sem(struct amd_iommu *iommu) +{ + u64 paddr; + + if (check_feature(FEATURE_SNP)) { + /* + * When SNP is enabled, the exclusion base register is used for the + * completion wait buffer (CWB) address. Read and re-use it. + */ + pr_info_once("Re-using CWB buffers from the previous kernel\n"); + paddr =3D readq(iommu->mmio_base + MMIO_EXCL_BASE_OFFSET) & PM_ADDR_MASK; + iommu->cmd_sem =3D iommu_memremap(paddr, PAGE_SIZE); + if (!iommu->cmd_sem) + return -ENOMEM; + iommu->cmd_sem_paddr =3D paddr; + } else { + return alloc_cwwb_sem(iommu); + } + + return 0; +} + +static int __init alloc_iommu_buffers(struct amd_iommu *iommu) +{ + int ret; + + /* + * Reuse/Remap the previous kernel's allocated completion wait + * command and event buffers for kdump boot. + */ + if (is_kdump_kernel()) { + ret =3D remap_or_alloc_cwwb_sem(iommu); + if (ret) + return ret; + + ret =3D remap_command_buffer(iommu); + if (ret) + return ret; + + ret =3D remap_event_buffer(iommu); + if (ret) + return ret; + } else { + ret =3D alloc_cwwb_sem(iommu); + if (ret) + return ret; + + ret =3D alloc_command_buffer(iommu); + if (ret) + return ret; + + ret =3D alloc_event_buffer(iommu); + if (ret) + return ret; + } + + return 0; } =20 static void __init free_cwwb_sem(struct amd_iommu *iommu) @@ -951,6 +1054,38 @@ static void __init free_cwwb_sem(struct amd_iommu *io= mmu) if (iommu->cmd_sem) iommu_free_pages((void *)iommu->cmd_sem); } +static void __init unmap_cwwb_sem(struct amd_iommu *iommu) +{ + if (iommu->cmd_sem) { + if (check_feature(FEATURE_SNP)) + memunmap((void *)iommu->cmd_sem); + else + iommu_free_pages((void *)iommu->cmd_sem); + } +} + +static void __init unmap_command_buffer(struct amd_iommu *iommu) +{ + memunmap((void *)iommu->cmd_buf); +} + +static void __init unmap_event_buffer(struct amd_iommu *iommu) +{ + memunmap(iommu->evt_buf); +} + +static void __init free_iommu_buffers(struct amd_iommu *iommu) +{ + if (is_kdump_kernel()) { + unmap_cwwb_sem(iommu); + unmap_command_buffer(iommu); + unmap_event_buffer(iommu); + } else { + free_cwwb_sem(iommu); + free_command_buffer(iommu); + free_event_buffer(iommu); + } +} =20 static void iommu_enable_xt(struct amd_iommu *iommu) { @@ -1655,9 +1790,7 @@ static void __init free_sysfs(struct amd_iommu *iommu) static void __init free_iommu_one(struct amd_iommu *iommu) { free_sysfs(iommu); - free_cwwb_sem(iommu); - free_command_buffer(iommu); - free_event_buffer(iommu); + free_iommu_buffers(iommu); amd_iommu_free_ppr_log(iommu); free_ga_log(iommu); iommu_unmap_mmio_space(iommu); @@ -1821,14 +1954,9 @@ static int __init init_iommu_one_late(struct amd_iom= mu *iommu) { int ret; =20 - if (alloc_cwwb_sem(iommu)) - return -ENOMEM; - - if (alloc_command_buffer(iommu)) - return -ENOMEM; - - if (alloc_event_buffer(iommu)) - return -ENOMEM; + ret =3D alloc_iommu_buffers(iommu); + if (ret) + return ret; =20 iommu->int_enabled =3D false; =20 diff --git a/drivers/iommu/amd/iommu.c b/drivers/iommu/amd/iommu.c index eb348c63a8d0..05a9ab3da1a3 100644 --- a/drivers/iommu/amd/iommu.c +++ b/drivers/iommu/amd/iommu.c @@ -1195,7 +1195,7 @@ static void build_completion_wait(struct iommu_cmd *c= md, struct amd_iommu *iommu, u64 data) { - u64 paddr =3D iommu_virt_to_phys((void *)iommu->cmd_sem); + u64 paddr =3D iommu->cmd_sem_paddr; =20 memset(cmd, 0, sizeof(*cmd)); cmd->data[0] =3D lower_32_bits(paddr) | CMD_COMPL_WAIT_STORE_MASK; 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X-OriginatorOrg: amd.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 25 Aug 2025 21:46:29.3638 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: 489a995a-421d-4ee3-7184-08dde420d968 X-MS-Exchange-CrossTenant-Id: 3dd8961f-e488-4e60-8e11-a82d994e183d X-MS-Exchange-CrossTenant-OriginalAttributedTenantConnectingIp: TenantId=3dd8961f-e488-4e60-8e11-a82d994e183d;Ip=[165.204.84.17];Helo=[SATLEXMB04.amd.com] X-MS-Exchange-CrossTenant-AuthSource: BN3PEPF0000B371.namprd21.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Anonymous X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem X-MS-Exchange-Transport-CrossTenantHeadersStamped: DS4PR12MB9561 Content-Type: text/plain; charset="utf-8" From: Ashish Kalra After a panic if SNP is enabled in the previous kernel then the kdump kernel boots with IOMMU SNP enforcement still enabled. IOMMU device table register is locked and exclusive to the previous kernel. Attempts to copy old device table from the previous kernel fails in kdump kernel as hardware ignores writes to the locked device table base address register as per AMD IOMMU spec Section 2.12.2.1. This causes the IOMMU driver (OS) and the hardware to reference different memory locations. As a result, the IOMMU hardware cannot process the command which results in repeated "Completion-Wait loop timed out" errors and a second kernel panic: "Kernel panic - not syncing: timer doesn't work through Interrupt-remapped IO-APIC". Reuse device table instead of copying device table in case of kdump boot and remove all copying device table code. Reviewed-by: Vasant Hegde Tested-by: Sairaj Kodilkar Signed-off-by: Ashish Kalra --- drivers/iommu/amd/init.c | 104 +++++++++++++-------------------------- 1 file changed, 34 insertions(+), 70 deletions(-) diff --git a/drivers/iommu/amd/init.c b/drivers/iommu/amd/init.c index 5b8e9d6befa5..dac6282675da 100644 --- a/drivers/iommu/amd/init.c +++ b/drivers/iommu/amd/init.c @@ -406,6 +406,9 @@ static void iommu_set_device_table(struct amd_iommu *io= mmu) =20 BUG_ON(iommu->mmio_base =3D=3D NULL); =20 + if (is_kdump_kernel()) + return; + entry =3D iommu_virt_to_phys(dev_table); entry |=3D (dev_table_size >> 12) - 1; memcpy_toio(iommu->mmio_base + MMIO_DEV_TABLE_OFFSET, @@ -646,7 +649,10 @@ static inline int __init alloc_dev_table(struct amd_io= mmu_pci_seg *pci_seg) =20 static inline void free_dev_table(struct amd_iommu_pci_seg *pci_seg) { - iommu_free_pages(pci_seg->dev_table); + if (is_kdump_kernel()) + memunmap((void *)pci_seg->dev_table); + else + iommu_free_pages(pci_seg->dev_table); pci_seg->dev_table =3D NULL; } =20 @@ -1117,15 +1123,12 @@ static void set_dte_bit(struct dev_table_entry *dte= , u8 bit) dte->data[i] |=3D (1UL << _bit); } =20 -static bool __copy_device_table(struct amd_iommu *iommu) +static bool __reuse_device_table(struct amd_iommu *iommu) { - u64 int_ctl, int_tab_len, entry =3D 0; struct amd_iommu_pci_seg *pci_seg =3D iommu->pci_seg; - struct dev_table_entry *old_devtb =3D NULL; - u32 lo, hi, devid, old_devtb_size; + u32 lo, hi, old_devtb_size; phys_addr_t old_devtb_phys; - u16 dom_id, dte_v, irq_v; - u64 tmp; + u64 entry; =20 /* Each IOMMU use separate device table with the same size */ lo =3D readl(iommu->mmio_base + MMIO_DEV_TABLE_OFFSET); @@ -1150,66 +1153,20 @@ static bool __copy_device_table(struct amd_iommu *i= ommu) pr_err("The address of old device table is above 4G, not trustworthy!\n"= ); return false; } - old_devtb =3D (cc_platform_has(CC_ATTR_HOST_MEM_ENCRYPT) && is_kdump_kern= el()) - ? (__force void *)ioremap_encrypted(old_devtb_phys, - pci_seg->dev_table_size) - : memremap(old_devtb_phys, pci_seg->dev_table_size, MEMREMAP_WB); - - if (!old_devtb) - return false; =20 - pci_seg->old_dev_tbl_cpy =3D iommu_alloc_pages_sz( - GFP_KERNEL | GFP_DMA32, pci_seg->dev_table_size); + /* + * Re-use the previous kernel's device table for kdump. + */ + pci_seg->old_dev_tbl_cpy =3D iommu_memremap(old_devtb_phys, pci_seg->dev_= table_size); if (pci_seg->old_dev_tbl_cpy =3D=3D NULL) { - pr_err("Failed to allocate memory for copying old device table!\n"); - memunmap(old_devtb); + pr_err("Failed to remap memory for reusing old device table!\n"); return false; } =20 - for (devid =3D 0; devid <=3D pci_seg->last_bdf; ++devid) { - pci_seg->old_dev_tbl_cpy[devid] =3D old_devtb[devid]; - dom_id =3D old_devtb[devid].data[1] & DEV_DOMID_MASK; - dte_v =3D old_devtb[devid].data[0] & DTE_FLAG_V; - - if (dte_v && dom_id) { - pci_seg->old_dev_tbl_cpy[devid].data[0] =3D old_devtb[devid].data[0]; - pci_seg->old_dev_tbl_cpy[devid].data[1] =3D old_devtb[devid].data[1]; - /* Reserve the Domain IDs used by previous kernel */ - if (ida_alloc_range(&pdom_ids, dom_id, dom_id, GFP_ATOMIC) !=3D dom_id)= { - pr_err("Failed to reserve domain ID 0x%x\n", dom_id); - memunmap(old_devtb); - return false; - } - /* If gcr3 table existed, mask it out */ - if (old_devtb[devid].data[0] & DTE_FLAG_GV) { - tmp =3D (DTE_GCR3_30_15 | DTE_GCR3_51_31); - pci_seg->old_dev_tbl_cpy[devid].data[1] &=3D ~tmp; - tmp =3D (DTE_GCR3_14_12 | DTE_FLAG_GV); - pci_seg->old_dev_tbl_cpy[devid].data[0] &=3D ~tmp; - } - } - - irq_v =3D old_devtb[devid].data[2] & DTE_IRQ_REMAP_ENABLE; - int_ctl =3D old_devtb[devid].data[2] & DTE_IRQ_REMAP_INTCTL_MASK; - int_tab_len =3D old_devtb[devid].data[2] & DTE_INTTABLEN_MASK; - if (irq_v && (int_ctl || int_tab_len)) { - if ((int_ctl !=3D DTE_IRQ_REMAP_INTCTL) || - (int_tab_len !=3D DTE_INTTABLEN_512 && - int_tab_len !=3D DTE_INTTABLEN_2K)) { - pr_err("Wrong old irq remapping flag: %#x\n", devid); - memunmap(old_devtb); - return false; - } - - pci_seg->old_dev_tbl_cpy[devid].data[2] =3D old_devtb[devid].data[2]; - } - } - memunmap(old_devtb); - return true; } =20 -static bool copy_device_table(void) +static bool reuse_device_table(void) { struct amd_iommu *iommu; struct amd_iommu_pci_seg *pci_seg; @@ -1217,17 +1174,17 @@ static bool copy_device_table(void) if (!amd_iommu_pre_enabled) return false; =20 - pr_warn("Translation is already enabled - trying to copy translation stru= ctures\n"); + pr_warn("Translation is already enabled - trying to reuse translation str= uctures\n"); =20 /* * All IOMMUs within PCI segment shares common device table. - * Hence copy device table only once per PCI segment. + * Hence reuse device table only once per PCI segment. */ for_each_pci_segment(pci_seg) { for_each_iommu(iommu) { if (pci_seg->id !=3D iommu->pci_seg->id) continue; - if (!__copy_device_table(iommu)) + if (!__reuse_device_table(iommu)) return false; break; } @@ -2906,8 +2863,8 @@ static void early_enable_iommu(struct amd_iommu *iomm= u) * This function finally enables all IOMMUs found in the system after * they have been initialized. * - * Or if in kdump kernel and IOMMUs are all pre-enabled, try to copy - * the old content of device table entries. Not this case or copy failed, + * Or if in kdump kernel and IOMMUs are all pre-enabled, try to reuse + * the old content of device table entries. Not this case or reuse failed, * just continue as normal kernel does. */ static void early_enable_iommus(void) @@ -2915,18 +2872,25 @@ static void early_enable_iommus(void) struct amd_iommu *iommu; struct amd_iommu_pci_seg *pci_seg; =20 - if (!copy_device_table()) { + if (!reuse_device_table()) { /* - * If come here because of failure in copying device table from old + * If come here because of failure in reusing device table from old * kernel with all IOMMUs enabled, print error message and try to * free allocated old_dev_tbl_cpy. */ - if (amd_iommu_pre_enabled) - pr_err("Failed to copy DEV table from previous kernel.\n"); + if (amd_iommu_pre_enabled) { + pr_err("Failed to reuse DEV table from previous kernel.\n"); + /* + * Bail out early if unable to remap/reuse DEV table from + * previous kernel if SNP enabled as IOMMU commands will + * time out without DEV table and cause kdump boot panic. + */ + BUG_ON(check_feature(FEATURE_SNP)); + } =20 for_each_pci_segment(pci_seg) { if (pci_seg->old_dev_tbl_cpy !=3D NULL) { - iommu_free_pages(pci_seg->old_dev_tbl_cpy); 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X-OriginatorOrg: amd.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 25 Aug 2025 21:46:48.8710 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: 44d3819d-c6e1-4049-1b8b-08dde420e509 X-MS-Exchange-CrossTenant-Id: 3dd8961f-e488-4e60-8e11-a82d994e183d X-MS-Exchange-CrossTenant-OriginalAttributedTenantConnectingIp: TenantId=3dd8961f-e488-4e60-8e11-a82d994e183d;Ip=[165.204.84.17];Helo=[SATLEXMB04.amd.com] X-MS-Exchange-CrossTenant-AuthSource: BN3PEPF0000B374.namprd21.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Anonymous X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem X-MS-Exchange-Transport-CrossTenantHeadersStamped: SJ0PR12MB8090 Content-Type: text/plain; charset="utf-8" From: Ashish Kalra Since SEV or SNP may already be initialized in the previous kernel, attempting to initialize them again in the kdump kernel can result in SNP initialization failures, which in turn lead to IOMMU initialization failures. Moreover, SNP/SEV guests are not run under a kdump kernel, so there is no need to initialize SEV or SNP during kdump boot. Skip SNP and SEV INIT if doing kdump boot. Tested-by: Sairaj Kodilkar Signed-off-by: Ashish Kalra --- drivers/crypto/ccp/sev-dev.c | 10 ++++++++++ 1 file changed, 10 insertions(+) diff --git a/drivers/crypto/ccp/sev-dev.c b/drivers/crypto/ccp/sev-dev.c index 4f000dc2e639..b701908c0bdc 100644 --- a/drivers/crypto/ccp/sev-dev.c +++ b/drivers/crypto/ccp/sev-dev.c @@ -28,6 +28,7 @@ #include #include #include +#include =20 #include #include @@ -1374,6 +1375,15 @@ static int __sev_platform_init_locked(int *error) if (!psp_master || !psp_master->sev_data) return -ENODEV; =20 + /* + * Skip SNP/SEV initialization under a kdump kernel as SEV/SNP + * may already be initialized in the previous kernel. 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Mon, 25 Aug 2025 21:47:06 +0000 X-MS-Exchange-Authentication-Results: spf=pass (sender IP is 165.204.84.17) smtp.mailfrom=amd.com; dkim=none (message not signed) header.d=none;dmarc=pass action=none header.from=amd.com; Received-SPF: Pass (protection.outlook.com: domain of amd.com designates 165.204.84.17 as permitted sender) receiver=protection.outlook.com; client-ip=165.204.84.17; helo=SATLEXMB04.amd.com; pr=C Received: from SATLEXMB04.amd.com (165.204.84.17) by BN3PEPF0000B370.mail.protection.outlook.com (10.167.243.167) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.20.9094.0 via Frontend Transport; Mon, 25 Aug 2025 21:47:06 +0000 Received: from ethanolx7e2ehost.amd.com (10.180.168.240) by SATLEXMB04.amd.com (10.181.40.145) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.1.2507.39; Mon, 25 Aug 2025 16:47:03 -0500 From: Ashish Kalra To: , , , , , CC: , , , , , , , , , , Subject: [PATCH v6 4/4] iommu/amd: Skip enabling command/event buffers for kdump Date: Mon, 25 Aug 2025 21:46:53 +0000 Message-ID: <576445eb4f168b467b0fc789079b650ca7c5b037.1756157913.git.ashish.kalra@amd.com> X-Mailer: git-send-email 2.34.1 In-Reply-To: References: Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable X-ClientProxiedBy: SATLEXMB04.amd.com (10.181.40.145) To SATLEXMB04.amd.com (10.181.40.145) X-EOPAttributedMessage: 0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: BN3PEPF0000B370:EE_|DS7PR12MB5886:EE_ X-MS-Office365-Filtering-Correlation-Id: 86d8131e-90a7-43d0-ec8f-08dde420ef90 X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|376014|7416014|1800799024|36860700013|82310400026; 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X-OriginatorOrg: amd.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 25 Aug 2025 21:47:06.5387 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: 86d8131e-90a7-43d0-ec8f-08dde420ef90 X-MS-Exchange-CrossTenant-Id: 3dd8961f-e488-4e60-8e11-a82d994e183d X-MS-Exchange-CrossTenant-OriginalAttributedTenantConnectingIp: TenantId=3dd8961f-e488-4e60-8e11-a82d994e183d;Ip=[165.204.84.17];Helo=[SATLEXMB04.amd.com] X-MS-Exchange-CrossTenant-AuthSource: BN3PEPF0000B370.namprd21.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Anonymous X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem X-MS-Exchange-Transport-CrossTenantHeadersStamped: DS7PR12MB5886 Content-Type: text/plain; charset="utf-8" From: Ashish Kalra After a panic if SNP is enabled in the previous kernel then the kdump kernel boots with IOMMU SNP enforcement still enabled. IOMMU command buffers and event buffer registers remain locked and exclusive to the previous kernel. Attempts to enable command and event buffers in the kdump kernel will fail, as hardware ignores writes to the locked MMIO registers as per AMD IOMMU spec Section 2.12.2.1. Skip enabling command buffers and event buffers for kdump boot as they are already enabled in the previous kernel. Reviewed-by: Vasant Hegde Tested-by: Sairaj Kodilkar Signed-off-by: Ashish Kalra --- drivers/iommu/amd/init.c | 28 +++++++++++++++++++--------- 1 file changed, 19 insertions(+), 9 deletions(-) diff --git a/drivers/iommu/amd/init.c b/drivers/iommu/amd/init.c index dac6282675da..d179344ad598 100644 --- a/drivers/iommu/amd/init.c +++ b/drivers/iommu/amd/init.c @@ -821,11 +821,16 @@ static void iommu_enable_command_buffer(struct amd_io= mmu *iommu) =20 BUG_ON(iommu->cmd_buf =3D=3D NULL); =20 - entry =3D iommu_virt_to_phys(iommu->cmd_buf); - entry |=3D MMIO_CMD_SIZE_512; - - memcpy_toio(iommu->mmio_base + MMIO_CMD_BUF_OFFSET, - &entry, sizeof(entry)); + if (!is_kdump_kernel()) { + /* + * Command buffer is re-used for kdump kernel and setting + * of MMIO register is not required. + */ + entry =3D iommu_virt_to_phys(iommu->cmd_buf); + entry |=3D MMIO_CMD_SIZE_512; + memcpy_toio(iommu->mmio_base + MMIO_CMD_BUF_OFFSET, + &entry, sizeof(entry)); + } =20 amd_iommu_reset_cmd_buffer(iommu); } @@ -876,10 +881,15 @@ static void iommu_enable_event_buffer(struct amd_iomm= u *iommu) =20 BUG_ON(iommu->evt_buf =3D=3D NULL); =20 - entry =3D iommu_virt_to_phys(iommu->evt_buf) | EVT_LEN_MASK; - - memcpy_toio(iommu->mmio_base + MMIO_EVT_BUF_OFFSET, - &entry, sizeof(entry)); + if (!is_kdump_kernel()) { + /* + * Event buffer is re-used for kdump kernel and setting + * of MMIO register is not required. + */ + entry =3D iommu_virt_to_phys(iommu->evt_buf) | EVT_LEN_MASK; + memcpy_toio(iommu->mmio_base + MMIO_EVT_BUF_OFFSET, + &entry, sizeof(entry)); + } =20 /* set head and tail to zero manually */ writel(0x00, iommu->mmio_base + MMIO_EVT_HEAD_OFFSET); --=20 2.34.1