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b=U2K9Yivm50F6Dikl0wVZ4cSj03rPDT67RK3RFOy89O0FC09etOSFuRif0VrC6tA2dyetKkAnQ2VCeJa4x/KO6cXxtwPgwDCe32uMF2vMJvWdE+Jo6iJ5TUUth++ETISYioK3N/Ex+3/g0eXWnmzclQIOOJv3NqMr5CjJMRtonMU= Authentication-Results: dkim=none (message not signed) header.d=none;dmarc=none action=none header.from=amd.com; Received: from DS7PR12MB6048.namprd12.prod.outlook.com (2603:10b6:8:9f::5) by IA1PR12MB6236.namprd12.prod.outlook.com (2603:10b6:208:3e4::19) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.9052.14; Thu, 21 Aug 2025 11:45:38 +0000 Received: from DS7PR12MB6048.namprd12.prod.outlook.com ([fe80::6318:26e5:357a:74a5]) by DS7PR12MB6048.namprd12.prod.outlook.com ([fe80::6318:26e5:357a:74a5%4]) with mapi id 15.20.9052.013; Thu, 21 Aug 2025 11:45:37 +0000 Message-ID: <4281e562-0dfa-41a0-bcff-02b7bb1d67ca@amd.com> Date: Thu, 21 Aug 2025 17:15:27 +0530 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v5 2/4] iommu/amd: Reuse device table for kdump To: Ashish Kalra , joro@8bytes.org, suravee.suthikulpanit@amd.com, thomas.lendacky@amd.com, Sairaj.ArunKodilkar@amd.com, herbert@gondor.apana.org.au Cc: seanjc@google.com, pbonzini@redhat.com, will@kernel.org, robin.murphy@arm.com, john.allen@amd.com, davem@davemloft.net, michael.roth@amd.com, iommu@lists.linux.dev, linux-kernel@vger.kernel.org, linux-crypto@vger.kernel.org, kvm@vger.kernel.org References: <5ad4c4525a2fd673cabcc763f0ccdb9b3595aaf4.1753911773.git.ashish.kalra@amd.com> Content-Language: en-US From: Vasant Hegde In-Reply-To: <5ad4c4525a2fd673cabcc763f0ccdb9b3595aaf4.1753911773.git.ashish.kalra@amd.com> Content-Type: text/plain; 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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. > Can you please expand and add something like below so that actually issue is clear. This causes the IOMMU driver (OS) and the hardware to reference different memory locations. As a result, the IOMMU hardware cannot process the command. > 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. > > Tested-by: Sairaj Kodilkar > Signed-off-by: Ashish Kalra Few minor nits. Otherwise patch looks ok. Reviewed-by: Vasant Hegde > --- > drivers/iommu/amd/init.c | 106 +++++++++++++-------------------------- > 1 file changed, 36 insertions(+), 70 deletions(-) > > diff --git a/drivers/iommu/amd/init.c b/drivers/iommu/amd/init.c > index aae1aa7723a5..05d9c1764883 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()) > + 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; > } > > @@ -1129,15 +1135,12 @@ 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); > @@ -1162,66 +1165,22 @@ 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. Can you please reword as its reusing crash kernel device table in all scenarios ? -Vasant