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b=lETYgikQBOo61GjnroISkFcJj6arA9k00NDLemD7PTcGwyY8gKNW3bX0+UdEO89R7Jywz1Q+V8JPVB0mCCWJ4DNh9wdJ8qemAhZt9G0x9x60vVJQYalBxFx2KHBFrXz430+rlUhbfSBJmjvL8nQ4X4skaDEIy9StJ7G9O/sI3Dw= Authentication-Results: dkim=none (message not signed) header.d=none;dmarc=none action=none header.from=amd.com; Received: from BL3PR12MB9049.namprd12.prod.outlook.com (2603:10b6:208:3b8::21) by SJ2PR12MB8062.namprd12.prod.outlook.com (2603:10b6:a03:4c8::22) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.8901.28; Thu, 17 Jul 2025 06:51:41 +0000 Received: from BL3PR12MB9049.namprd12.prod.outlook.com ([fe80::ae6a:9bdd:af5b:e9ad]) by BL3PR12MB9049.namprd12.prod.outlook.com ([fe80::ae6a:9bdd:af5b:e9ad%6]) with mapi id 15.20.8901.024; Thu, 17 Jul 2025 06:51:41 +0000 Message-ID: Date: Thu, 17 Jul 2025 01:51:37 -0500 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v3 2/4] iommu/amd: Reuse device table for kdump To: Vasant Hegde , 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, bp@alien8.de, michael.roth@amd.com, iommu@lists.linux.dev, linux-kernel@vger.kernel.org, linux-crypto@vger.kernel.org, kvm@vger.kernel.org References: <42842f0455c1439327aaa593ef22576ef97c16ee.1752605725.git.ashish.kalra@amd.com> <7db3a4b2-dff6-4391-a642-b4c374646ca7@amd.com> <7f08c03f-a618-4ea4-ab57-f7078afe49c9@amd.com> <40cc4c41-c16a-40b1-a2c2-591f29216b94@amd.com> Content-Language: en-US From: "Kalra, Ashish" In-Reply-To: <40cc4c41-c16a-40b1-a2c2-591f29216b94@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. >>>> >>>> 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? >>> >>> > > .../... > >>>> 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. > > But what is the point is proceeding when we know its going to fail? I think its > better to fail here so that at least we know where/why it failed. > Yes that makes sense. As Sairaj suggested, we can add a BUG_ON() if reuse_device_table() fails in case of SNP enabled. Thanks, Ashish