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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