>-----Original Message-----
>From: Eric Auger <eric.au...@redhat.com>
>Subject: Re: [PATCH v2 13/19] intel_iommu: Stick to system MR for
>IOMMUFD backed host device when x-fls=on
>
>
>
>On 6/20/25 9:18 AM, Zhenzhong Duan wrote:
>> When guest in scalable mode and x-flts=on, we stick to system MR for
>IOMMUFD
>when guest works in scalable mode ?
>> backed host device. Then its default hwpt contains GPA->HPA mappings
>which is
>> used directly if PGTT=PT and used as nested parent if PGTT=FLT. Otherwise
>> fallback to original processing.
>>
>> Suggested-by: Yi Liu <yi.l....@intel.com>
>> Signed-off-by: Zhenzhong Duan <zhenzhong.d...@intel.com>
>> ---
>> hw/i386/intel_iommu.c | 24 ++++++++++++++++++++++++
>> 1 file changed, 24 insertions(+)
>>
>> diff --git a/hw/i386/intel_iommu.c b/hw/i386/intel_iommu.c
>> index ed71bb8ec7..be01f8885f 100644
>> --- a/hw/i386/intel_iommu.c
>> +++ b/hw/i386/intel_iommu.c
>> @@ -1779,6 +1779,7 @@ static bool
>vtd_dev_pt_enabled(IntelIOMMUState *s, VTDContextEntry *ce,
>> */
>> return false;
>> }
>> +
>spurious new line
Will fix.
>> return (VTD_PE_GET_TYPE(&pe) == VTD_SM_PASID_ENTRY_PT);
>> }
>>
>> @@ -1790,10 +1791,33 @@ static bool
>vtd_as_pt_enabled(VTDAddressSpace *as)
>> {
>> IntelIOMMUState *s;
>> VTDContextEntry ce;
>> + struct vtd_as_key key = {
>> + .bus = as->bus,
>> + .devfn = as->devfn,
>> + };
>>
>> assert(as);
>>
>> s = as->iommu_state;
>> +
>> + /*
>> + * When guest in scalable mode and x-flts=on, we stick to system MR
>ditto
That's strange, I didn't see spurious new line here.
>> + * for IOMMUFD backed host device. Then its default hwpt contains
>> + * GPA->HPA mappings which is used directly if PGTT=PT and used as
>> + * nested parent if PGTT=FLT. Otherwise fallback to original
>fall back here and above
>
>This comment sounds a little bit unrelated to the below implementation
>which does not refer to system MR. how does the search for the hiod
>relate to that. I would refocus the comment.
vtd_as_pt_enabled()'s return value determines which MR to switch to.
See vtd_switch_address_space(). How about adding a comment:
+/*
+ * vtd_switch_address_space() calls vtd_as_pt_enabled() to determine which
+ * MR to switch to. Switch to system MR if return true, iommu MR otherwise.
+ */
static bool vtd_as_pt_enabled(VTDAddressSpace *as)
{
With this comment, we know the return value impact MR switch and this patch
deal with return value.
Thanks
Zhenzhong
