Nouveau - Jun 2023 - [PATCH 2/4] x86: always initialize xen-swiotlb when xen-pcifront is enabling

On 07.06.23 15:12, Christoph Hellwig wrote:
> On Mon, May 22, 2023 at 10:37:09AM +0200, Juergen Gross wrote:
>> In normal cases PCI passthrough in PV guests requires to start the
guest
>> with e820_host=1. So it should be rather easy to limit allocating the
>> 64MB in PV guests to the cases where the memory map has non-RAM regions
>> especially in the first 1MB of the memory.
>>
>> This will cover even hotplug cases. The only case not covered would be
a
>> guest started with e820_host=1 even if no PCI passthrough was planned.
>> But this should be rather rare (at least I hope so).
> 
> So is this an ACK for the patch and can we go ahead with it?
As long as above mentioned check of the E820 map is done, yes.

If you want I can send a diff to be folded into your patch on Monday.
> 
> (I'd still like to merge swiotlb-xen into swiotlb eventually, but
it's
> probably not going to happen this merge window)
Would be nice.


Juergen
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On Fri, Jun 09, 2023 at 05:38:28PM +0200, Juergen Gross
wrote:
>>> guest started with e820_host=1 even if no PCI passthrough was
planned.
>>> But this should be rather rare (at least I hope so).
>>
>> So is this an ACK for the patch and can we go ahead with it?
>
> As long as above mentioned check of the E820 map is done, yes.
>
> If you want I can send a diff to be folded into your patch on Monday.
Yes, that would be great!

On 09.06.23 17:38, Juergen Gross wrote:
> On 07.06.23 15:12, Christoph Hellwig wrote:
>> On Mon, May 22, 2023 at 10:37:09AM +0200, Juergen Gross wrote:
>>> In normal cases PCI passthrough in PV guests requires to start the
guest
>>> with e820_host=1. So it should be rather easy to limit allocating
the
>>> 64MB in PV guests to the cases where the memory map has non-RAM
regions
>>> especially in the first 1MB of the memory.
>>>
>>> This will cover even hotplug cases. The only case not covered would
be a
>>> guest started with e820_host=1 even if no PCI passthrough was
planned.
>>> But this should be rather rare (at least I hope so).
>>
>> So is this an ACK for the patch and can we go ahead with it?
> 
> As long as above mentioned check of the E820 map is done, yes.
> 
> If you want I can send a diff to be folded into your patch on Monday.
Attached is a patch for adding a new flag xen_pv_pci_possible. You can
either add the patch to your series or merge it into your patch 2.

You need to modify your patch like this:

@@ -111,7 +90,10 @@ static inline void __init pci_xen_swiotlb_init(void)
  void __init pci_iommu_alloc(void)
  {
  	if (xen_pv_domain()) {
-		if (xen_initial_domain() || x86_swiotlb_enable)
+		if (xen_initial_domain() ||
+		    (IS_ENABLED(CONFIG_XEN_PCIDEV_FRONTEND) &&
+		     xen_pv_pci_possible) ||
+		    x86_swiotlb_enable)
  			pci_xen_swiotlb_init();
  		return;
  	}


Juergen
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