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

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Message-ID: <6c0710c3-cffb-48db-872d-96e2e836fbdd@amd.com>
Date: Thu, 20 Nov 2025 12:26:46 +0530
From: Vasant Hegde <vasant.hegde@....com>
To: Jason Gunthorpe <jgg@...dia.com>
Cc: Sairaj Kodilkar <sarunkod@....com>, iommu@...ts.linux.dev,
 linux-kernel@...r.kernel.org, joro@...tes.org,
 suravee.suthikulpanit@....com, ashish.kalra@....com, robin.murphy@....com,
 will@...nel.org
Subject: Re: [PATCH 1/2] amd/iommu: Preserve domain ids inside the kdump
 kernel



On 11/19/2025 7:13 PM, Jason Gunthorpe wrote:
> On Wed, Nov 19, 2025 at 04:20:28PM +0530, Vasant Hegde wrote:
>>> 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;
>>> +
>>> +		if (!dte_v || !dom_id)
>>> +			continue;
>>> +		/*
>>> +		 * ID reseveration can fail with -ENOSPC when there
>>> +		 * 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);
> 
> Is it really an atomic context? Why?


I had to dig git history to figureout why I used GFP_ATOMIC for ida allocator.

When we moved to ida allocator we used GPF_ATOMIC as there were paths were code
was holding spinlock before calling ida allocator.

Now that those paths are moved to mutex lock and remvoed redundant locks, I
think its fine to change it to GFP_KERNEL.

-Vasant