linux-kernel - Re: [PATCH 1/2] amd/iommu: Preserve domain ids inside the kdump kernel

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Message-ID: <7wueupy7eekotvlskujbg3ltfx5moc7g46oaseadpud2gkeea2@x2k254g6aqcq>
Date: Mon, 17 Nov 2025 05:21:35 +0000
From: Ankit Soni <Ankit.Soni@....com>
To: Sairaj Kodilkar <sarunkod@....com>
CC: <iommu@...ts.linux.dev>, <linux-kernel@...r.kernel.org>,
	<joro@...tes.org>, <suravee.suthikulpanit@....com>, <vasant.hegde@....com>,
	<ashish.kalra@....com>, <robin.murphy@....com>, <will@...nel.org>
Subject: Re: [PATCH 1/2] amd/iommu: Preserve domain ids inside the kdump
 kernel


Hi,

On Fri, Nov 14, 2025 at 04:14:41PM +0530, Sairaj Kodilkar wrote:
> Currently AMD IOMMU driver does not reserve domain ids programmed in the
> DTE while reusing the device table inside kdump kernel. This can cause
> reallocation of these domain ids for newer domains that are created by
> the kdump kernel, which can lead to potential IO_PAGE_FAULTs
> 
> Hence reserve these ids inside pdom_ids.
> 
> Fixes: 38e5f33ee359 ("iommu/amd: Reuse device table for kdump")
> Signed-off-by: Sairaj Kodilkar <sarunkod@....com>
> ---
>  drivers/iommu/amd/init.c | 25 ++++++++++++++++++++++++-
>  1 file changed, 24 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/iommu/amd/init.c b/drivers/iommu/amd/init.c
> index f2991c11867c..9375fba1071c 100644
> --- a/drivers/iommu/amd/init.c
> +++ b/drivers/iommu/amd/init.c
> @@ -1136,9 +1136,13 @@ static void set_dte_bit(struct dev_table_entry *dte, u8 bit)
>  static bool __reuse_device_table(struct amd_iommu *iommu)
>  {
>  	struct amd_iommu_pci_seg *pci_seg = iommu->pci_seg;
> -	u32 lo, hi, old_devtb_size;
> +	struct dev_table_entry *old_dev_tbl_entry;
> +	u32 lo, hi, old_devtb_size, devid;
>  	phys_addr_t old_devtb_phys;
> +	u16 dom_id;
> +	bool dte_v;
>  	u64 entry;
> +	int ret;
>  
>  	/* Each IOMMU use separate device table with the same size */
>  	lo = readl(iommu->mmio_base + MMIO_DEV_TABLE_OFFSET);
> @@ -1173,6 +1177,25 @@ static bool __reuse_device_table(struct amd_iommu *iommu)
>  		return false;
>  	}
>  
> +	for (devid = 0; devid <= pci_seg->last_bdf; devid++) {
> +		old_dev_tbl_entry = &pci_seg->old_dev_tbl_cpy[devid];
> +		dte_v = old_dev_tbl_entry->data[0] & DTE_FLAG_V;
> +		dom_id = old_dev_tbl_entry->data[1] & DEV_DOMID_MASK;

Consider using FIELD_GET().

> +
> +		if (!dte_v || !dom_id)
> +			continue;
> +		/*
> +		 * ID reseveration can fail with -ENOSPC when there

s/reseveration/reservation

> +		 * are multiple devices present in the same domain,
> +		 * hence check only for -ENOMEM.
> +		 */
> +		ret = ida_alloc_range(&pdom_ids, dom_id, dom_id, GFP_ATOMIC);
> +		if (ret == -ENOMEM) {
> +			pr_err("Failed to reserve domain ID 0x%x\n", dom_id);

Can we use ratelimit, as in kdump kernel pr_err can be bit noisy.

-Ankit

> +			return false;
> +		}
> +	}
> +
>  	return true;
>  }
>  
> -- 
> 2.34.1
>