[PATCH 0/2] amd/iommu: Preserve domain ids inside the kdump kernel

[PATCH 0/2] amd/iommu: Preserve domain ids inside the kdump kernel

[Sairaj Kodilkar]

Patch 1: Reserves the Domain IDs allocated by the host kernel while reusing its
	 device table inside kdump kernel
Patch 2: Cleanup around pdom allocation

Fixes: 38e5f33ee359 ("iommu/amd: Reuse device table for kdump")
Signed-off-by: Sairaj Kodilkar <sarunkod@amd.com>

Sairaj Kodilkar (2):
  amd/iommu: Preserve domain ids inside the kdump kernel
  amd/iommu: Make protection domain ID functions non-static

 drivers/iommu/amd/amd_iommu.h |  5 +++++
 drivers/iommu/amd/init.c      | 26 +++++++++++++++++++++++---
 drivers/iommu/amd/iommu.c     | 27 ++++++++++++++++++---------
 3 files changed, 46 insertions(+), 12 deletions(-)

-- 
2.34.1

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

[Sairaj Kodilkar]

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@amd.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;
+
+		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);
+		if (ret == -ENOMEM) {
+			pr_err("Failed to reserve domain ID 0x%x\n", dom_id);
+			return false;
+		}
+	}
+
 	return true;
 }
 
-- 
2.34.1

[PATCH 2/2] amd/iommu: Make protection domain ID functions non-static

[Sairaj Kodilkar]

So that both iommu.c and init.c can utilize them. Also define a new
function 'pdom_id_destroy()' to destroy 'pdom_ids' instead of directly
calling ida functions.

Signed-off-by: Sairaj Kodilkar <sarunkod@amd.com>
---
 drivers/iommu/amd/amd_iommu.h |  5 +++++
 drivers/iommu/amd/init.c      |  7 ++-----
 drivers/iommu/amd/iommu.c     | 27 ++++++++++++++++++---------
 3 files changed, 25 insertions(+), 14 deletions(-)

diff --git a/drivers/iommu/amd/amd_iommu.h b/drivers/iommu/amd/amd_iommu.h
index 25044d28f28a..6335b577f80d 100644
--- a/drivers/iommu/amd/amd_iommu.h
+++ b/drivers/iommu/amd/amd_iommu.h
@@ -173,6 +173,11 @@ static inline struct protection_domain *to_pdomain(struct iommu_domain *dom)
 bool translation_pre_enabled(struct amd_iommu *iommu);
 int __init add_special_device(u8 type, u8 id, u32 *devid, bool cmd_line);
 
+int amd_iommu_pdom_id_alloc(void);
+int amd_iommu_pdom_id_reserve(int id);
+void amd_iommu_pdom_id_free(int id);
+void amd_iommu_pdom_id_destroy(void);
+
 #ifdef CONFIG_DMI
 void amd_iommu_apply_ivrs_quirks(void);
 #else
diff --git a/drivers/iommu/amd/init.c b/drivers/iommu/amd/init.c
index 9375fba1071c..c78fa67f34c6 100644
--- a/drivers/iommu/amd/init.c
+++ b/drivers/iommu/amd/init.c
@@ -1142,7 +1142,6 @@ static bool __reuse_device_table(struct amd_iommu *iommu)
 	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);
@@ -1189,8 +1188,7 @@ static bool __reuse_device_table(struct amd_iommu *iommu)
 		 * 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) {
+		if (amd_iommu_pdom_id_reserve(dom_id) == -ENOMEM) {
 			pr_err("Failed to reserve domain ID 0x%x\n", dom_id);
 			return false;
 		}
@@ -3134,8 +3132,7 @@ static bool __init check_ioapic_information(void)
 
 static void __init free_dma_resources(void)
 {
-	ida_destroy(&pdom_ids);
-
+	amd_iommu_pdom_id_destroy();
 	free_unity_maps();
 }
 
diff --git a/drivers/iommu/amd/iommu.c b/drivers/iommu/amd/iommu.c
index 48bca4dc8eb6..4d57e820b824 100644
--- a/drivers/iommu/amd/iommu.c
+++ b/drivers/iommu/amd/iommu.c
@@ -1785,17 +1785,26 @@ int amd_iommu_complete_ppr(struct device *dev, u32 pasid, int status, int tag)
  * contain.
  *
  ****************************************************************************/
-
-static int pdom_id_alloc(void)
+int amd_iommu_pdom_id_alloc(void)
 {
 	return ida_alloc_range(&pdom_ids, 1, MAX_DOMAIN_ID - 1, GFP_ATOMIC);
 }
 
-static void pdom_id_free(int id)
+int amd_iommu_pdom_id_reserve(int id)
+{
+	return ida_alloc_range(&pdom_ids, id, id, GFP_ATOMIC);
+}
+
+void amd_iommu_pdom_id_free(int id)
 {
 	ida_free(&pdom_ids, id);
 }
 
+void amd_iommu_pdom_id_destroy(void)
+{
+	ida_destroy(&pdom_ids);
+}
+
 static void free_gcr3_tbl_level1(u64 *tbl)
 {
 	u64 *ptr;
@@ -1838,7 +1847,7 @@ static void free_gcr3_table(struct gcr3_tbl_info *gcr3_info)
 	gcr3_info->glx = 0;
 
 	/* Free per device domain ID */
-	pdom_id_free(gcr3_info->domid);
+	amd_iommu_pdom_id_free(gcr3_info->domid);
 
 	iommu_free_pages(gcr3_info->gcr3_tbl);
 	gcr3_info->gcr3_tbl = NULL;
@@ -1874,14 +1883,14 @@ static int setup_gcr3_table(struct gcr3_tbl_info *gcr3_info,
 		return -EBUSY;
 
 	/* Allocate per device domain ID */
-	domid = pdom_id_alloc();
+	domid = amd_iommu_pdom_id_alloc();
 	if (domid <= 0)
 		return -ENOSPC;
 	gcr3_info->domid = domid;
 
 	gcr3_info->gcr3_tbl = iommu_alloc_pages_node_sz(nid, GFP_ATOMIC, SZ_4K);
 	if (gcr3_info->gcr3_tbl == NULL) {
-		pdom_id_free(domid);
+		amd_iommu_pdom_id_free(domid);
 		return -ENOMEM;
 	}
 
@@ -2477,7 +2486,7 @@ struct protection_domain *protection_domain_alloc(void)
 	if (!domain)
 		return NULL;
 
-	domid = pdom_id_alloc();
+	domid = amd_iommu_pdom_id_alloc();
 	if (domid <= 0) {
 		kfree(domain);
 		return NULL;
@@ -2773,7 +2782,7 @@ void amd_iommu_domain_free(struct iommu_domain *dom)
 
 	WARN_ON(!list_empty(&domain->dev_list));
 	pt_iommu_deinit(&domain->iommu);
-	pdom_id_free(domain->id);
+	amd_iommu_pdom_id_free(domain->id);
 	kfree(domain);
 }
 
@@ -2824,7 +2833,7 @@ void amd_iommu_init_identity_domain(void)
 	domain->ops = &identity_domain_ops;
 	domain->owner = &amd_iommu_ops;
 
-	identity_domain.id = pdom_id_alloc();
+	identity_domain.id = amd_iommu_pdom_id_alloc();
 
 	protection_domain_init(&identity_domain);
 }
-- 
2.34.1

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

[Ankit Soni]

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@amd.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
> 

Re: [PATCH 2/2] amd/iommu: Make protection domain ID functions non-static

[Vasant Hegde]

On 11/14/2025 4:14 PM, Sairaj Kodilkar wrote:
> So that both iommu.c and init.c can utilize them. Also define a new
> function 'pdom_id_destroy()' to destroy 'pdom_ids' instead of directly
> calling ida functions.
> 
> Signed-off-by: Sairaj Kodilkar <sarunkod@amd.com>

Reviewed-by: Vasant Hegde <vasant.hegde@amd.com>


-Vasant

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

[Vasant Hegde]

On 11/14/2025 4:14 PM, 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@amd.com>

I missed to inform you. This was reported by Jason while reviewing nested
series. So

Reported-by: Jason Gunthorpe <jgg@nvidia.com>
Reviewed-by: Vasant Hegde <vasant.hegde@amd.com>

-Vasant

> ---
>  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;
> +
> +		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);
> +		if (ret == -ENOMEM) {
> +			pr_err("Failed to reserve domain ID 0x%x\n", dom_id);
> +			return false;
> +		}
> +	}
> +
>  	return true;
>  }
>  

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

[Jason Gunthorpe]

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?

> > +		if (ret == -ENOMEM) {
> > +			pr_err("Failed to reserve domain ID 0x%x\n", dom_id);
> > +			return false;

Please don't print on ENOMEM, there is already a print.

I think you should also keep iterating as other dom_ids may still be
fit in already allocated bitmaps. Though the system is probably toast
if this happens anyhow.

Jason

Re: [PATCH 2/2] amd/iommu: Make protection domain ID functions non-static

[Jason Gunthorpe]

On Fri, Nov 14, 2025 at 04:14:42PM +0530, Sairaj Kodilkar wrote:
> So that both iommu.c and init.c can utilize them. Also define a new
> function 'pdom_id_destroy()' to destroy 'pdom_ids' instead of directly
> calling ida functions.
> 
> Signed-off-by: Sairaj Kodilkar <sarunkod@amd.com>
> ---
>  drivers/iommu/amd/amd_iommu.h |  5 +++++
>  drivers/iommu/amd/init.c      |  7 ++-----
>  drivers/iommu/amd/iommu.c     | 27 ++++++++++++++++++---------
>  3 files changed, 25 insertions(+), 14 deletions(-)
> 
> diff --git a/drivers/iommu/amd/amd_iommu.h b/drivers/iommu/amd/amd_iommu.h
> index 25044d28f28a..6335b577f80d 100644
> --- a/drivers/iommu/amd/amd_iommu.h
> +++ b/drivers/iommu/amd/amd_iommu.h
> @@ -173,6 +173,11 @@ static inline struct protection_domain *to_pdomain(struct iommu_domain *dom)
>  bool translation_pre_enabled(struct amd_iommu *iommu);
>  int __init add_special_device(u8 type, u8 id, u32 *devid, bool cmd_line);
>  
> +int amd_iommu_pdom_id_alloc(void);
> +int amd_iommu_pdom_id_reserve(int id);
> +void amd_iommu_pdom_id_free(int id);
> +void amd_iommu_pdom_id_destroy(void);

Domain IDs are not signed integers. Use u32.

> diff --git a/drivers/iommu/amd/iommu.c b/drivers/iommu/amd/iommu.c
> index 48bca4dc8eb6..4d57e820b824 100644
> --- a/drivers/iommu/amd/iommu.c
> +++ b/drivers/iommu/amd/iommu.c
> @@ -1785,17 +1785,26 @@ int amd_iommu_complete_ppr(struct device *dev, u32 pasid, int status, int tag)
>   * contain.
>   *
>   ****************************************************************************/
> -
> -static int pdom_id_alloc(void)
> +int amd_iommu_pdom_id_alloc(void)
>  {
>  	return ida_alloc_range(&pdom_ids, 1, MAX_DOMAIN_ID - 1, GFP_ATOMIC);
>  }
>
> -static void pdom_id_free(int id)
> +int amd_iommu_pdom_id_reserve(int id)
> +{
> +	return ida_alloc_range(&pdom_ids, id, id, GFP_ATOMIC);
> +}

The GFP should probably be passed in as a function argument

Jason

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

[Sairaj Kodilkar]

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?

No, its not atomic context. My intension was to ensure that the memory 
allocation
succeeds. But I am not sure if it's the most appropriate choice for this 
scenario

Could you please suggest which GFP flag would be best suited for this use ?


>
>>> +		if (ret == -ENOMEM) {
>>> +			pr_err("Failed to reserve domain ID 0x%x\n", dom_id);
>>> +			return false;
> Please don't print on ENOMEM, there is already a print.
>
> I think you should also keep iterating as other dom_ids may still be
> fit in already allocated bitmaps. Though the system is probably toast
> if this happens anyhow.

Sure


Thanks
Sairaj
> Jason

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

[Vasant Hegde]

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?
> 
>>> +		if (ret == -ENOMEM) {
>>> +			pr_err("Failed to reserve domain ID 0x%x\n", dom_id);
>>> +			return false;
> 
> Please don't print on ENOMEM, there is already a print.
> 
> I think you should also keep iterating as other dom_ids may still be
> fit in already allocated bitmaps. Though the system is probably toast
> if this happens anyhow.

Right. No point in continuing if it fails to reserve the domain ID. Things can
go wrong. So it returns error.

-Vasant

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

[Vasant Hegde]

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

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

[Jason Gunthorpe]

On Thu, Nov 20, 2025 at 10:32:32AM +0530, Sairaj Kodilkar wrote:

> No, its not atomic context. My intension was to ensure that the
> memory allocation succeeds. But I am not sure if it's the most
> appropriate choice for this scenario

This is early boot, it won't fail either way. Use GFP_KERNEL because
it is clearer

Jason

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

[Sairaj Kodilkar]

On 11/20/2025 6:26 PM, Jason Gunthorpe wrote:
> On Thu, Nov 20, 2025 at 10:32:32AM +0530, Sairaj Kodilkar wrote:
>
>> No, its not atomic context. My intension was to ensure that the
>> memory allocation succeeds. But I am not sure if it's the most
>> appropriate choice for this scenario
> This is early boot, it won't fail either way. Use GFP_KERNEL because
> it is clearer

Sure, Thanks for suggestion

-Sairaj