On 7/31/2025 3:26 AM, Ashish Kalra wrote:
> From: Ashish Kalra <ashish.kalra@xxxxxxx>
>
> 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.
>
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 <sarunkod@xxxxxxx>
> Signed-off-by: Ashish Kalra <ashish.kalra@xxxxxxx>
Few minor nits. Otherwise patch looks ok.
Reviewed-by: Vasant Hegde <vasant.hegde@xxxxxxx>
> ---
> 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
