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client-ip=165.204.84.17; helo=SATLEXMB04.amd.com; pr=C Received: from SATLEXMB04.amd.com (165.204.84.17) by CH3PEPF0000000F.mail.protection.outlook.com (10.167.244.40) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.20.8943.21 via Frontend Transport; Thu, 17 Jul 2025 05:39:08 +0000 Received: from [10.252.206.76] (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; Thu, 17 Jul 2025 00:39:01 -0500 Message-ID: <8869fcdb-5a4a-45c7-a1ff-1ade5b85097d@amd.com> Date: Thu, 17 Jul 2025 11:08:58 +0530 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v3 2/4] iommu/amd: Reuse device table for kdump To: "Kalra, Ashish" , Vasant Hegde , , , , , CC: , , , , , , , , , , , References: <42842f0455c1439327aaa593ef22576ef97c16ee.1752605725.git.ashish.kalra@amd.com> <7db3a4b2-dff6-4391-a642-b4c374646ca7@amd.com> <7f08c03f-a618-4ea4-ab57-f7078afe49c9@amd.com> Content-Language: en-US From: Sairaj Kodilkar In-Reply-To: <7f08c03f-a618-4ea4-ab57-f7078afe49c9@amd.com> Content-Type: text/plain; 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X-OriginatorOrg: amd.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 17 Jul 2025 05:39:08.6391 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: ac5bb09c-c490-4f91-f499-08ddc4f44055 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: CH3PEPF0000000F.namprd04.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Anonymous X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem X-MS-Exchange-Transport-CrossTenantHeadersStamped: IA1PR12MB6652 On 7/17/2025 3:37 AM, Kalra, Ashish wrote: > Hello Vasant, > > On 7/16/2025 4:42 AM, Vasant Hegde wrote: >> >> >> On 7/16/2025 12:57 AM, Ashish Kalra wrote: >>> 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 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. >>> >>> Signed-off-by: Ashish Kalra >>> --- >>> drivers/iommu/amd/init.c | 97 ++++++++++++---------------------------- >>> 1 file changed, 28 insertions(+), 69 deletions(-) >>> >>> diff --git a/drivers/iommu/amd/init.c b/drivers/iommu/amd/init.c >>> index 32295f26be1b..18bd869a82d9 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 *iommu) >>> >>> BUG_ON(iommu->mmio_base == NULL); >>> >>> + if (is_kdump_kernel()) >> >> This is fine.. but its becoming too many places with kdump check! I don't know >> what is the better way here. >> Is it worth to keep it like this -OR- add say iommu ops that way during init we >> check is_kdump_kernel() and adjust the ops ? >> >> @Joerg, any preference? >> >> >>> + return; >>> + >>> entry = iommu_virt_to_phys(dev_table); >>> entry |= (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_iommu_pci_seg *pci_seg) >>> >>> 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 = NULL; >>> } >>> >>> @@ -1128,15 +1134,12 @@ static void set_dte_bit(struct dev_table_entry *dte, u8 bit) >>> dte->data[i] |= (1UL << _bit); >>> } >>> >>> -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 = 0; >>> struct amd_iommu_pci_seg *pci_seg = iommu->pci_seg; >>> - struct dev_table_entry *old_devtb = 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; >>> >>> /* Each IOMMU use separate device table with the same size */ >>> lo = readl(iommu->mmio_base + MMIO_DEV_TABLE_OFFSET); >>> @@ -1161,66 +1164,22 @@ static bool __copy_device_table(struct amd_iommu *iommu) >>> pr_err("The address of old device table is above 4G, not trustworthy!\n"); >>> return false; >>> } >>> - old_devtb = (cc_platform_has(CC_ATTR_HOST_MEM_ENCRYPT) && is_kdump_kernel()) >>> - ? (__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; >>> >>> - pci_seg->old_dev_tbl_cpy = iommu_alloc_pages_sz( >>> - GFP_KERNEL | GFP_DMA32, pci_seg->dev_table_size); >>> + /* >>> + * IOMMU Device Table Base Address MMIO register is locked >>> + * if SNP is enabled during kdump, reuse the previous kernel's >>> + * device table. >>> + */ >>> + pci_seg->old_dev_tbl_cpy = iommu_memremap(old_devtb_phys, pci_seg->dev_table_size); >>> if (pci_seg->old_dev_tbl_cpy == 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; >>> } >>> >>> - for (devid = 0; devid <= pci_seg->last_bdf; ++devid) { >>> - pci_seg->old_dev_tbl_cpy[devid] = old_devtb[devid]; >>> - dom_id = old_devtb[devid].data[1] & DEV_DOMID_MASK; >>> - dte_v = old_devtb[devid].data[0] & DTE_FLAG_V; >>> - >>> - if (dte_v && dom_id) { >>> - pci_seg->old_dev_tbl_cpy[devid].data[0] = old_devtb[devid].data[0]; >>> - pci_seg->old_dev_tbl_cpy[devid].data[1] = 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) != 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 = (DTE_GCR3_30_15 | DTE_GCR3_51_31); >>> - pci_seg->old_dev_tbl_cpy[devid].data[1] &= ~tmp; >>> - tmp = (DTE_GCR3_14_12 | DTE_FLAG_GV); >>> - pci_seg->old_dev_tbl_cpy[devid].data[0] &= ~tmp; >>> - } >>> - } >>> - >>> - irq_v = old_devtb[devid].data[2] & DTE_IRQ_REMAP_ENABLE; >>> - int_ctl = old_devtb[devid].data[2] & DTE_IRQ_REMAP_INTCTL_MASK; >>> - int_tab_len = old_devtb[devid].data[2] & DTE_INTTABLEN_MASK; >>> - if (irq_v && (int_ctl || int_tab_len)) { >>> - if ((int_ctl != DTE_IRQ_REMAP_INTCTL) || >>> - (int_tab_len != DTE_INTTABLEN_512 && >>> - int_tab_len != 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] = old_devtb[devid].data[2]; >>> - } >>> - } >>> - memunmap(old_devtb); >>> - >>> return true; >>> } >>> >>> -static bool copy_device_table(void) >>> +static bool reuse_device_table(void) >>> { >>> struct amd_iommu *iommu; >>> struct amd_iommu_pci_seg *pci_seg; >>> @@ -1228,17 +1187,17 @@ static bool copy_device_table(void) >>> if (!amd_iommu_pre_enabled) >>> return false; >>> >>> - pr_warn("Translation is already enabled - trying to copy translation structures\n"); >>> + pr_warn("Translation is already enabled - trying to reuse translation structures\n"); >>> >>> /* >>> * 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 != iommu->pci_seg->id) >>> continue; >>> - if (!__copy_device_table(iommu)) >>> + if (!__reuse_device_table(iommu)) >>> return false; >>> break; >>> } >>> @@ -2917,8 +2876,8 @@ static void early_enable_iommu(struct amd_iommu *iommu) >>> * 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) >>> @@ -2926,18 +2885,18 @@ static void early_enable_iommus(void) >>> struct amd_iommu *iommu; >>> struct amd_iommu_pci_seg *pci_seg; >>> >>> - if (!copy_device_table()) { >>> + if (!reuse_device_table()) { >> >> Hmmm. What happens if SNP enabled and reuse_device_table() couldn't setup >> previous DTE? >> In non-SNP case it works fine as we can rebuild new DTE. But in SNP case we >> should fail the kdump right? >> > > Which will happen automatically, if we can't setup previous DTE for SNP case > then IOMMU commands will time-out and subsequenly cause a panic as IRQ remapping > won't be setup. > > So this is as good as failing the kdump, which will have the same result. > Maybe we can have a BUG_ON() when it fails to remap the DTE in kdump kernel and SNP is turned on ? Its hard to understand why kdump has failed just by looking at completion wait timeout. Will be easier to debug with BUG_ON(). > Thanks, > Ashish >