[PATCH v1] vfio/pci: Avoid mapping BARs for devices with non-mappable BARs

[PATCH v1] vfio/pci: Avoid mapping BARs for devices with non-mappable BARs

[Farhan Ali]

vfio_pci_core_map_bars() calls pci_iomap() to set up BAR resources, but not
all devices support having their BARs mapped by the CPU. The
non_mappable_bars flag indicates that a PCI device's BARs cannot be
accessed by the CPU. The ISM device on s390 is one such device. The BAR
size for an ISM device is 256 TiB, and attempting to map the BAR will lead
to warnings:

vmalloc_node_range for size 281474976714752 failed: Address range
restricted to 0x2110bab00000 - 0x21903ab00000

Use pdev->non_mappable_bars to skip pci_iomap() for such devices. This flag
is set by the PCI core at enumeration time and already serves the same
purpose in vfio_pci_probe_mmaps().

Fixes: 05f2a68b407a ("vfio/pci: Set up BAR resources and maps in vfio_pci_core_enable()")
Reported-by: Christian Borntraeger <borntraeger@linux.ibm.com>
Signed-off-by: Farhan Ali <alifm@linux.ibm.com>
---
 drivers/vfio/pci/vfio_pci_core.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/drivers/vfio/pci/vfio_pci_core.c b/drivers/vfio/pci/vfio_pci_core.c
index 3f11a9624b9c..6a184588ff23 100644
--- a/drivers/vfio/pci/vfio_pci_core.c
+++ b/drivers/vfio/pci/vfio_pci_core.c
@@ -554,6 +554,9 @@ static void vfio_pci_core_map_bars(struct vfio_pci_core_device *vdev)
 
 		vdev->barmap[bar] = IOMEM_ERR_PTR(-ENODEV);
 
+		if (pdev->non_mappable_bars)
+			continue;
+
 		if (!pci_resource_len(pdev, i))
 			continue;
 
-- 
2.43.0

Re: [PATCH v1] vfio/pci: Avoid mapping BARs for devices with non-mappable BARs

[Matthew Rosato]

On 7/29/26 2:11 PM, Farhan Ali wrote:
> vfio_pci_core_map_bars() calls pci_iomap() to set up BAR resources, but not
> all devices support having their BARs mapped by the CPU. The
> non_mappable_bars flag indicates that a PCI device's BARs cannot be
> accessed by the CPU. The ISM device on s390 is one such device. The BAR
> size for an ISM device is 256 TiB, and attempting to map the BAR will lead
> to warnings:
> 
> vmalloc_node_range for size 281474976714752 failed: Address range
> restricted to 0x2110bab00000 - 0x21903ab00000
> 
> Use pdev->non_mappable_bars to skip pci_iomap() for such devices. This flag
> is set by the PCI core at enumeration time and already serves the same
> purpose in vfio_pci_probe_mmaps().
> 
> Fixes: 05f2a68b407a ("vfio/pci: Set up BAR resources and maps in vfio_pci_core_enable()")
> Reported-by: Christian Borntraeger <borntraeger@linux.ibm.com>
> Signed-off-by: Farhan Ali <alifm@linux.ibm.com>
> ---
>  drivers/vfio/pci/vfio_pci_core.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/drivers/vfio/pci/vfio_pci_core.c b/drivers/vfio/pci/vfio_pci_core.c
> index 3f11a9624b9c..6a184588ff23 100644
> --- a/drivers/vfio/pci/vfio_pci_core.c
> +++ b/drivers/vfio/pci/vfio_pci_core.c
> @@ -554,6 +554,9 @@ static void vfio_pci_core_map_bars(struct vfio_pci_core_device *vdev)
>  
>  		vdev->barmap[bar] = IOMEM_ERR_PTR(-ENODEV);
>  
> +		if (pdev->non_mappable_bars)
> +			continue;
> +

This would work for the ISM case at least, but I wonder: should we check
vdev->bar_mmap_supported[bar] instead?

My question boils down to: do we still want messages for some of the
cases where we set vdev->bar_mmap_supported[bar] = false in
vfio_pci_probe_mmaps()?

Or should the messages only print when we probed, thought the bar could
be mmap'd (vdev->bar_mmap_supported[bar] == true), and now hit a failure?

Thanks,
Matt

>  		if (!pci_resource_len(pdev, i))
>  			continue;
>  

Re: [PATCH v1] vfio/pci: Avoid mapping BARs for devices with non-mappable BARs

[Farhan Ali]

On 7/29/2026 12:41 PM, Matthew Rosato wrote:
> On 7/29/26 2:11 PM, Farhan Ali wrote:
>> vfio_pci_core_map_bars() calls pci_iomap() to set up BAR resources, but not
>> all devices support having their BARs mapped by the CPU. The
>> non_mappable_bars flag indicates that a PCI device's BARs cannot be
>> accessed by the CPU. The ISM device on s390 is one such device. The BAR
>> size for an ISM device is 256 TiB, and attempting to map the BAR will lead
>> to warnings:
>>
>> vmalloc_node_range for size 281474976714752 failed: Address range
>> restricted to 0x2110bab00000 - 0x21903ab00000
>>
>> Use pdev->non_mappable_bars to skip pci_iomap() for such devices. This flag
>> is set by the PCI core at enumeration time and already serves the same
>> purpose in vfio_pci_probe_mmaps().
>>
>> Fixes: 05f2a68b407a ("vfio/pci: Set up BAR resources and maps in vfio_pci_core_enable()")
>> Reported-by: Christian Borntraeger <borntraeger@linux.ibm.com>
>> Signed-off-by: Farhan Ali <alifm@linux.ibm.com>
>> ---
>>   drivers/vfio/pci/vfio_pci_core.c | 3 +++
>>   1 file changed, 3 insertions(+)
>>
>> diff --git a/drivers/vfio/pci/vfio_pci_core.c b/drivers/vfio/pci/vfio_pci_core.c
>> index 3f11a9624b9c..6a184588ff23 100644
>> --- a/drivers/vfio/pci/vfio_pci_core.c
>> +++ b/drivers/vfio/pci/vfio_pci_core.c
>> @@ -554,6 +554,9 @@ static void vfio_pci_core_map_bars(struct vfio_pci_core_device *vdev)
>>   
>>   		vdev->barmap[bar] = IOMEM_ERR_PTR(-ENODEV);
>>   
>> +		if (pdev->non_mappable_bars)
>> +			continue;
>> +
> This would work for the ISM case at least, but I wonder: should we check
> vdev->bar_mmap_supported[bar] instead?
>
> My question boils down to: do we still want messages for some of the
> cases where we set vdev->bar_mmap_supported[bar] = false in
> vfio_pci_probe_mmaps()?

AFAIU vfio_pci_probe_mmaps() is only called in 
vfio_pci_core_finish_enable(). Since vfio_pci_core_map_bars() is called 
in vfio_pci_core_enable(), and before vfio_pci_core_finish_enable(), 
bar_mmap_supported would be false here for all devices. So I don't think 
it would work here, unless I missed something?

Thanks

Farhan

>
> Or should the messages only print when we probed, thought the bar could
> be mmap'd (vdev->bar_mmap_supported[bar] == true), and now hit a failure?
>
> Thanks,
> Matt
>
>>   		if (!pci_resource_len(pdev, i))
>>   			continue;
>>   

Re: [PATCH v1] vfio/pci: Avoid mapping BARs for devices with non-mappable BARs

[Alex Williamson]

On Wed, 29 Jul 2026 13:28:46 -0700
Farhan Ali <alifm@linux.ibm.com> wrote:

> On 7/29/2026 12:41 PM, Matthew Rosato wrote:
> > On 7/29/26 2:11 PM, Farhan Ali wrote:  
> >> vfio_pci_core_map_bars() calls pci_iomap() to set up BAR resources, but not
> >> all devices support having their BARs mapped by the CPU. The
> >> non_mappable_bars flag indicates that a PCI device's BARs cannot be
> >> accessed by the CPU. The ISM device on s390 is one such device. The BAR
> >> size for an ISM device is 256 TiB, and attempting to map the BAR will lead
> >> to warnings:
> >>
> >> vmalloc_node_range for size 281474976714752 failed: Address range
> >> restricted to 0x2110bab00000 - 0x21903ab00000
> >>
> >> Use pdev->non_mappable_bars to skip pci_iomap() for such devices. This flag
> >> is set by the PCI core at enumeration time and already serves the same
> >> purpose in vfio_pci_probe_mmaps().
> >>
> >> Fixes: 05f2a68b407a ("vfio/pci: Set up BAR resources and maps in vfio_pci_core_enable()")
> >> Reported-by: Christian Borntraeger <borntraeger@linux.ibm.com>
> >> Signed-off-by: Farhan Ali <alifm@linux.ibm.com>
> >> ---
> >>   drivers/vfio/pci/vfio_pci_core.c | 3 +++
> >>   1 file changed, 3 insertions(+)
> >>
> >> diff --git a/drivers/vfio/pci/vfio_pci_core.c b/drivers/vfio/pci/vfio_pci_core.c
> >> index 3f11a9624b9c..6a184588ff23 100644
> >> --- a/drivers/vfio/pci/vfio_pci_core.c
> >> +++ b/drivers/vfio/pci/vfio_pci_core.c
> >> @@ -554,6 +554,9 @@ static void vfio_pci_core_map_bars(struct vfio_pci_core_device *vdev)
> >>   
> >>   		vdev->barmap[bar] = IOMEM_ERR_PTR(-ENODEV);
> >>   
> >> +		if (pdev->non_mappable_bars)
> >> +			continue;
> >> +  
> > This would work for the ISM case at least, but I wonder: should we check
> > vdev->bar_mmap_supported[bar] instead?
> >
> > My question boils down to: do we still want messages for some of the
> > cases where we set vdev->bar_mmap_supported[bar] = false in
> > vfio_pci_probe_mmaps()?  
> 
> AFAIU vfio_pci_probe_mmaps() is only called in 
> vfio_pci_core_finish_enable(). Since vfio_pci_core_map_bars() is called 
> in vfio_pci_core_enable(), and before vfio_pci_core_finish_enable(), 
> bar_mmap_supported would be false here for all devices. So I don't think 
> it would work here, unless I missed something?

Also IO Port and sub-page MMIO BARs are things that do exist.  Thanks,

Alex

Re: [PATCH v1] vfio/pci: Avoid mapping BARs for devices with non-mappable BARs

[Farhan Ali]

On 7/29/2026 1:36 PM, Alex Williamson wrote:
> On Wed, 29 Jul 2026 13:28:46 -0700
> Farhan Ali <alifm@linux.ibm.com> wrote:
>
>> On 7/29/2026 12:41 PM, Matthew Rosato wrote:
>>> On 7/29/26 2:11 PM, Farhan Ali wrote:
>>>> vfio_pci_core_map_bars() calls pci_iomap() to set up BAR resources, but not
>>>> all devices support having their BARs mapped by the CPU. The
>>>> non_mappable_bars flag indicates that a PCI device's BARs cannot be
>>>> accessed by the CPU. The ISM device on s390 is one such device. The BAR
>>>> size for an ISM device is 256 TiB, and attempting to map the BAR will lead
>>>> to warnings:
>>>>
>>>> vmalloc_node_range for size 281474976714752 failed: Address range
>>>> restricted to 0x2110bab00000 - 0x21903ab00000
>>>>
>>>> Use pdev->non_mappable_bars to skip pci_iomap() for such devices. This flag
>>>> is set by the PCI core at enumeration time and already serves the same
>>>> purpose in vfio_pci_probe_mmaps().
>>>>
>>>> Fixes: 05f2a68b407a ("vfio/pci: Set up BAR resources and maps in vfio_pci_core_enable()")
>>>> Reported-by: Christian Borntraeger <borntraeger@linux.ibm.com>
>>>> Signed-off-by: Farhan Ali <alifm@linux.ibm.com>
>>>> ---
>>>>    drivers/vfio/pci/vfio_pci_core.c | 3 +++
>>>>    1 file changed, 3 insertions(+)
>>>>
>>>> diff --git a/drivers/vfio/pci/vfio_pci_core.c b/drivers/vfio/pci/vfio_pci_core.c
>>>> index 3f11a9624b9c..6a184588ff23 100644
>>>> --- a/drivers/vfio/pci/vfio_pci_core.c
>>>> +++ b/drivers/vfio/pci/vfio_pci_core.c
>>>> @@ -554,6 +554,9 @@ static void vfio_pci_core_map_bars(struct vfio_pci_core_device *vdev)
>>>>    
>>>>    		vdev->barmap[bar] = IOMEM_ERR_PTR(-ENODEV);
>>>>    
>>>> +		if (pdev->non_mappable_bars)
>>>> +			continue;
>>>> +
>>> This would work for the ISM case at least, but I wonder: should we check
>>> vdev->bar_mmap_supported[bar] instead?
>>>
>>> My question boils down to: do we still want messages for some of the
>>> cases where we set vdev->bar_mmap_supported[bar] = false in
>>> vfio_pci_probe_mmaps()?
>> AFAIU vfio_pci_probe_mmaps() is only called in
>> vfio_pci_core_finish_enable(). Since vfio_pci_core_map_bars() is called
>> in vfio_pci_core_enable(), and before vfio_pci_core_finish_enable(),
>> bar_mmap_supported would be false here for all devices. So I don't think
>> it would work here, unless I missed something?
> Also IO Port and sub-page MMIO BARs are things that do exist.  Thanks,
>
> Alex

Just to clarify, are you suggesting we expand this check to also avoid 
mapping IO port and sub-page MMIO BARs?

Thanks

Farhan

Re: [PATCH v1] vfio/pci: Avoid mapping BARs for devices with non-mappable BARs

[Alex Williamson]

On Wed, 29 Jul 2026 14:32:45 -0700
Farhan Ali <alifm@linux.ibm.com> wrote:

> On 7/29/2026 1:36 PM, Alex Williamson wrote:
> > On Wed, 29 Jul 2026 13:28:46 -0700
> > Farhan Ali <alifm@linux.ibm.com> wrote:
> >  
> >> On 7/29/2026 12:41 PM, Matthew Rosato wrote:  
> >>> On 7/29/26 2:11 PM, Farhan Ali wrote:  
> >>>> vfio_pci_core_map_bars() calls pci_iomap() to set up BAR resources, but not
> >>>> all devices support having their BARs mapped by the CPU. The
> >>>> non_mappable_bars flag indicates that a PCI device's BARs cannot be
> >>>> accessed by the CPU. The ISM device on s390 is one such device. The BAR
> >>>> size for an ISM device is 256 TiB, and attempting to map the BAR will lead
> >>>> to warnings:
> >>>>
> >>>> vmalloc_node_range for size 281474976714752 failed: Address range
> >>>> restricted to 0x2110bab00000 - 0x21903ab00000
> >>>>
> >>>> Use pdev->non_mappable_bars to skip pci_iomap() for such devices. This flag
> >>>> is set by the PCI core at enumeration time and already serves the same
> >>>> purpose in vfio_pci_probe_mmaps().
> >>>>
> >>>> Fixes: 05f2a68b407a ("vfio/pci: Set up BAR resources and maps in vfio_pci_core_enable()")
> >>>> Reported-by: Christian Borntraeger <borntraeger@linux.ibm.com>
> >>>> Signed-off-by: Farhan Ali <alifm@linux.ibm.com>
> >>>> ---
> >>>>    drivers/vfio/pci/vfio_pci_core.c | 3 +++
> >>>>    1 file changed, 3 insertions(+)
> >>>>
> >>>> diff --git a/drivers/vfio/pci/vfio_pci_core.c b/drivers/vfio/pci/vfio_pci_core.c
> >>>> index 3f11a9624b9c..6a184588ff23 100644
> >>>> --- a/drivers/vfio/pci/vfio_pci_core.c
> >>>> +++ b/drivers/vfio/pci/vfio_pci_core.c
> >>>> @@ -554,6 +554,9 @@ static void vfio_pci_core_map_bars(struct vfio_pci_core_device *vdev)
> >>>>    
> >>>>    		vdev->barmap[bar] = IOMEM_ERR_PTR(-ENODEV);
> >>>>    
> >>>> +		if (pdev->non_mappable_bars)
> >>>> +			continue;
> >>>> +  
> >>> This would work for the ISM case at least, but I wonder: should we check
> >>> vdev->bar_mmap_supported[bar] instead?
> >>>
> >>> My question boils down to: do we still want messages for some of the
> >>> cases where we set vdev->bar_mmap_supported[bar] = false in
> >>> vfio_pci_probe_mmaps()?  
> >> AFAIU vfio_pci_probe_mmaps() is only called in
> >> vfio_pci_core_finish_enable(). Since vfio_pci_core_map_bars() is called
> >> in vfio_pci_core_enable(), and before vfio_pci_core_finish_enable(),
> >> bar_mmap_supported would be false here for all devices. So I don't think
> >> it would work here, unless I missed something?  
> > Also IO Port and sub-page MMIO BARs are things that do exist.  Thanks,
> 
> Just to clarify, are you suggesting we expand this check to also avoid 
> mapping IO port and sub-page MMIO BARs?

Sorry, no, I'm not.  I think we're conflating that the barmap is
related to mmap access.  The barmap itself is holding the iomap of the
BAR, used for read/write.  The only real relation to the mmap is that
we request the resource via this path as well.

Therefore not only is the ordering of setting up bar_mmap_supported
wrong, it's flagging entirely the wrong thing here and keying on it
would entirely break IO port and sub-page MMIO BAR access.  Thanks,

Alex

Re: [PATCH v1] vfio/pci: Avoid mapping BARs for devices with non-mappable BARs

[Farhan Ali]

On 7/29/2026 2:50 PM, Alex Williamson wrote:
> On Wed, 29 Jul 2026 14:32:45 -0700
> Farhan Ali <alifm@linux.ibm.com> wrote:
>
>> On 7/29/2026 1:36 PM, Alex Williamson wrote:
>>> On Wed, 29 Jul 2026 13:28:46 -0700
>>> Farhan Ali <alifm@linux.ibm.com> wrote:
>>>   
>>>> On 7/29/2026 12:41 PM, Matthew Rosato wrote:
>>>>> On 7/29/26 2:11 PM, Farhan Ali wrote:
>>>>>> vfio_pci_core_map_bars() calls pci_iomap() to set up BAR resources, but not
>>>>>> all devices support having their BARs mapped by the CPU. The
>>>>>> non_mappable_bars flag indicates that a PCI device's BARs cannot be
>>>>>> accessed by the CPU. The ISM device on s390 is one such device. The BAR
>>>>>> size for an ISM device is 256 TiB, and attempting to map the BAR will lead
>>>>>> to warnings:
>>>>>>
>>>>>> vmalloc_node_range for size 281474976714752 failed: Address range
>>>>>> restricted to 0x2110bab00000 - 0x21903ab00000
>>>>>>
>>>>>> Use pdev->non_mappable_bars to skip pci_iomap() for such devices. This flag
>>>>>> is set by the PCI core at enumeration time and already serves the same
>>>>>> purpose in vfio_pci_probe_mmaps().
>>>>>>
>>>>>> Fixes: 05f2a68b407a ("vfio/pci: Set up BAR resources and maps in vfio_pci_core_enable()")
>>>>>> Reported-by: Christian Borntraeger <borntraeger@linux.ibm.com>
>>>>>> Signed-off-by: Farhan Ali <alifm@linux.ibm.com>
>>>>>> ---
>>>>>>     drivers/vfio/pci/vfio_pci_core.c | 3 +++
>>>>>>     1 file changed, 3 insertions(+)
>>>>>>
>>>>>> diff --git a/drivers/vfio/pci/vfio_pci_core.c b/drivers/vfio/pci/vfio_pci_core.c
>>>>>> index 3f11a9624b9c..6a184588ff23 100644
>>>>>> --- a/drivers/vfio/pci/vfio_pci_core.c
>>>>>> +++ b/drivers/vfio/pci/vfio_pci_core.c
>>>>>> @@ -554,6 +554,9 @@ static void vfio_pci_core_map_bars(struct vfio_pci_core_device *vdev)
>>>>>>     
>>>>>>     		vdev->barmap[bar] = IOMEM_ERR_PTR(-ENODEV);
>>>>>>     
>>>>>> +		if (pdev->non_mappable_bars)
>>>>>> +			continue;
>>>>>> +
>>>>> This would work for the ISM case at least, but I wonder: should we check
>>>>> vdev->bar_mmap_supported[bar] instead?
>>>>>
>>>>> My question boils down to: do we still want messages for some of the
>>>>> cases where we set vdev->bar_mmap_supported[bar] = false in
>>>>> vfio_pci_probe_mmaps()?
>>>> AFAIU vfio_pci_probe_mmaps() is only called in
>>>> vfio_pci_core_finish_enable(). Since vfio_pci_core_map_bars() is called
>>>> in vfio_pci_core_enable(), and before vfio_pci_core_finish_enable(),
>>>> bar_mmap_supported would be false here for all devices. So I don't think
>>>> it would work here, unless I missed something?
>>> Also IO Port and sub-page MMIO BARs are things that do exist.  Thanks,
>> Just to clarify, are you suggesting we expand this check to also avoid
>> mapping IO port and sub-page MMIO BARs?
> Sorry, no, I'm not.  I think we're conflating that the barmap is
> related to mmap access.  The barmap itself is holding the iomap of the
> BAR, used for read/write.  The only real relation to the mmap is that
> we request the resource via this path as well.
>
> Therefore not only is the ordering of setting up bar_mmap_supported
> wrong, it's flagging entirely the wrong thing here and keying on it
> would entirely break IO port and sub-page MMIO BAR access.  Thanks,
>
> Alex

Hi Alex,

I wanted some guidance on how we should proceed with this patch? The 
warning messages are a regression on s390 for ISM devices, so we would 
like to fix it.

Thanks

Farhan

Re: [PATCH v1] vfio/pci: Avoid mapping BARs for devices with non-mappable BARs

[Farhan Ali]

On 8/3/2026 12:54 PM, Alex Williamson wrote:
> On Mon, 3 Aug 2026 09:39:19 -0700
> Farhan Ali <alifm@linux.ibm.com> wrote:
>
>> On 7/29/2026 2:50 PM, Alex Williamson wrote:
>>> On Wed, 29 Jul 2026 14:32:45 -0700
>>> Farhan Ali <alifm@linux.ibm.com> wrote:
>>>   
>>>> On 7/29/2026 1:36 PM, Alex Williamson wrote:
>>>>> On Wed, 29 Jul 2026 13:28:46 -0700
>>>>> Farhan Ali <alifm@linux.ibm.com> wrote:
>>>>>      
>>>>>> On 7/29/2026 12:41 PM, Matthew Rosato wrote:
>>>>>>> On 7/29/26 2:11 PM, Farhan Ali wrote:
>>>>>>>> vfio_pci_core_map_bars() calls pci_iomap() to set up BAR resources, but not
>>>>>>>> all devices support having their BARs mapped by the CPU. The
>>>>>>>> non_mappable_bars flag indicates that a PCI device's BARs cannot be
>>>>>>>> accessed by the CPU. The ISM device on s390 is one such device. The BAR
>>>>>>>> size for an ISM device is 256 TiB, and attempting to map the BAR will lead
>>>>>>>> to warnings:
>>>>>>>>
>>>>>>>> vmalloc_node_range for size 281474976714752 failed: Address range
>>>>>>>> restricted to 0x2110bab00000 - 0x21903ab00000
>>>>>>>>
>>>>>>>> Use pdev->non_mappable_bars to skip pci_iomap() for such devices. This flag
>>>>>>>> is set by the PCI core at enumeration time and already serves the same
>>>>>>>> purpose in vfio_pci_probe_mmaps().
>>>>>>>>
>>>>>>>> Fixes: 05f2a68b407a ("vfio/pci: Set up BAR resources and maps in vfio_pci_core_enable()")
>>>>>>>> Reported-by: Christian Borntraeger <borntraeger@linux.ibm.com>
>>>>>>>> Signed-off-by: Farhan Ali <alifm@linux.ibm.com>
>>>>>>>> ---
>>>>>>>>      drivers/vfio/pci/vfio_pci_core.c | 3 +++
>>>>>>>>      1 file changed, 3 insertions(+)
>>>>>>>>
>>>>>>>> diff --git a/drivers/vfio/pci/vfio_pci_core.c b/drivers/vfio/pci/vfio_pci_core.c
>>>>>>>> index 3f11a9624b9c..6a184588ff23 100644
>>>>>>>> --- a/drivers/vfio/pci/vfio_pci_core.c
>>>>>>>> +++ b/drivers/vfio/pci/vfio_pci_core.c
>>>>>>>> @@ -554,6 +554,9 @@ static void vfio_pci_core_map_bars(struct vfio_pci_core_device *vdev)
>>>>>>>>      
>>>>>>>>      		vdev->barmap[bar] = IOMEM_ERR_PTR(-ENODEV);
>>>>>>>>      
>>>>>>>> +		if (pdev->non_mappable_bars)
>>>>>>>> +			continue;
>>>>>>>> +
>>>>>>> This would work for the ISM case at least, but I wonder: should we check
>>>>>>> vdev->bar_mmap_supported[bar] instead?
>>>>>>>
>>>>>>> My question boils down to: do we still want messages for some of the
>>>>>>> cases where we set vdev->bar_mmap_supported[bar] = false in
>>>>>>> vfio_pci_probe_mmaps()?
>>>>>> AFAIU vfio_pci_probe_mmaps() is only called in
>>>>>> vfio_pci_core_finish_enable(). Since vfio_pci_core_map_bars() is called
>>>>>> in vfio_pci_core_enable(), and before vfio_pci_core_finish_enable(),
>>>>>> bar_mmap_supported would be false here for all devices. So I don't think
>>>>>> it would work here, unless I missed something?
>>>>> Also IO Port and sub-page MMIO BARs are things that do exist.  Thanks,
>>>> Just to clarify, are you suggesting we expand this check to also avoid
>>>> mapping IO port and sub-page MMIO BARs?
>>> Sorry, no, I'm not.  I think we're conflating that the barmap is
>>> related to mmap access.  The barmap itself is holding the iomap of the
>>> BAR, used for read/write.  The only real relation to the mmap is that
>>> we request the resource via this path as well.
>>>
>>> Therefore not only is the ordering of setting up bar_mmap_supported
>>> wrong, it's flagging entirely the wrong thing here and keying on it
>>> would entirely break IO port and sub-page MMIO BAR access.  Thanks,
>>>
>>> Alex
>> Hi Alex,
>>
>> I wanted some guidance on how we should proceed with this patch? The
>> warning messages are a regression on s390 for ISM devices, so we would
>> like to fix it.
> I think the original proposal is probably the correct one.  The
> non_mmapable_bars flag doesn't restrict its application to specific BAR
> types or access, at least not beyond "can't be mapped to CPU or peers."
>
> If we can't map the BAR to the CPU, then we don't need to request the
> region or perform the pci_iomap(), which is what I understand explodes
> here.  Therefore we really only need to establish the errno in the
> barmap here.

Yes, its the call to pci_iomap() that leads to the warning.

>
> The bar_mmap_supported flag describes something else, whether the BAR
> can be mapped into the user address space.  My intention was only to
> point out that there are BARs that cannot be mapped to the user address
> space because either they're not MMIO or we can't safely map the full
> page, therefore bar_mmap_supported is an invalid test for whether we
> should request the region or iomap the BAR.
>
> Is there still a gap with the original proposal that I'm missing?

AFAICT this fix should be sufficient. I think Matt's question was to see 
if there were other cases for which bar_mmap_supported were set to 
false, that we need to consider here. But I will let him clarify to see 
if he has any concerns.

Thanks

Farhan

Re: [PATCH v1] vfio/pci: Avoid mapping BARs for devices with non-mappable BARs

[Matthew Rosato]

>> The bar_mmap_supported flag describes something else, whether the BAR
>> can be mapped into the user address space.  My intention was only to
>> point out that there are BARs that cannot be mapped to the user address
>> space because either they're not MMIO or we can't safely map the full
>> page, therefore bar_mmap_supported is an invalid test for whether we
>> should request the region or iomap the BAR.
>>
>> Is there still a gap with the original proposal that I'm missing?
> 
> AFAICT this fix should be sufficient. I think Matt's question was to see
> if there were other cases for which bar_mmap_supported were set to
> false, that we need to consider here. But I will let him clarify to see
> if he has any concerns.

^ Yes exactly that.  To be clear: I am happy from the s390 side with the
fix as it is proposed.

My questions were basically trying to generate the conversation that was
just had in an effort to avoid another fix later.

So, with the context provided (thanks!):

Reviewed-by: Matthew Rosato <mjrosato@linux.ibm.com>

Re: [PATCH v1] vfio/pci: Avoid mapping BARs for devices with non-mappable BARs

[Niklas Schnelle]

On Wed, 2026-07-29 at 11:11 -0700, Farhan Ali wrote:
> vfio_pci_core_map_bars() calls pci_iomap() to set up BAR resources, but not
> all devices support having their BARs mapped by the CPU. The
> non_mappable_bars flag indicates that a PCI device's BARs cannot be
> accessed by the CPU. The ISM device on s390 is one such device. The BAR
> size for an ISM device is 256 TiB, and attempting to map the BAR will lead
> to warnings:
> 
> vmalloc_node_range for size 281474976714752 failed: Address range
> restricted to 0x2110bab00000 - 0x21903ab00000
> 
> Use pdev->non_mappable_bars to skip pci_iomap() for such devices. This flag
> is set by the PCI core at enumeration time and already serves the same
> purpose in vfio_pci_probe_mmaps().
> 
> Fixes: 05f2a68b407a ("vfio/pci: Set up BAR resources and maps in vfio_pci_core_enable()")
> Reported-by: Christian Borntraeger <borntraeger@linux.ibm.com>
> Signed-off-by: Farhan Ali <alifm@linux.ibm.com>
> ---
>  drivers/vfio/pci/vfio_pci_core.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/drivers/vfio/pci/vfio_pci_core.c b/drivers/vfio/pci/vfio_pci_core.c
> index 3f11a9624b9c..6a184588ff23 100644
> --- a/drivers/vfio/pci/vfio_pci_core.c
> +++ b/drivers/vfio/pci/vfio_pci_core.c
> @@ -554,6 +554,9 @@ static void vfio_pci_core_map_bars(struct vfio_pci_core_device *vdev)
>  
>  		vdev->barmap[bar] = IOMEM_ERR_PTR(-ENODEV);
>  
> +		if (pdev->non_mappable_bars)
> +			continue;
> +
>  		if (!pci_resource_len(pdev, i))
>  			continue;
>  

While I was following the discussion I forgot to reply. This looks good
to me. Thank you for taking care of this. 

Feel free to add:

Reviewed-by: Niklas Schnelle <schnelle@linux.ibm.com>