Re: [PATCH v2 03/17] intel_iommu: Add a placeholder variable for scalable modern mode

[CLEMENT MATHIEU--DRIF]

On 13/08/2024 04:20, Duan, Zhenzhong wrote:
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>> -----Original Message-----
>> From: CLEMENT MATHIEU--DRIF <clement.mathieu--drif@eviden.com>
>> Subject: Re: [PATCH v2 03/17] intel_iommu: Add a placeholder variable for
>> scalable modern mode
>>
>>
>>
>> On 08/08/2024 14:31, Duan, Zhenzhong wrote:
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>>>
>>> On 8/6/2024 2:35 PM, CLEMENT MATHIEU--DRIF wrote:
>>>> On 05/08/2024 08:27, Zhenzhong Duan wrote:
>>>>> Caution: External email. Do not open attachments or click links,
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>>>>>
>>>>>
>>>>> Add an new element scalable_mode in IntelIOMMUState to mark
>> scalable
>>>>> modern mode, this element will be exposed as an intel_iommu property
>>>>> finally.
>>>>>
>>>>> For now, it's only a placehholder and used for address width
>>>>> compatibility check and block host device passthrough until nesting
>>>>> is supported.
>>>>>
>>>>> Signed-off-by: Yi Liu <yi.l.liu@intel.com>
>>>>> Signed-off-by: Zhenzhong Duan <zhenzhong.duan@intel.com>
>>>>> ---
>>>>>     include/hw/i386/intel_iommu.h |  1 +
>>>>>     hw/i386/intel_iommu.c         | 12 +++++++++---
>>>>>     2 files changed, 10 insertions(+), 3 deletions(-)
>>>>>
>>>>> diff --git a/include/hw/i386/intel_iommu.h
>>>>> b/include/hw/i386/intel_iommu.h
>>>>> index 1eb05c29fc..788ed42477 100644
>>>>> --- a/include/hw/i386/intel_iommu.h
>>>>> +++ b/include/hw/i386/intel_iommu.h
>>>>> @@ -262,6 +262,7 @@ struct IntelIOMMUState {
>>>>>
>>>>>         bool caching_mode;              /* RO - is cap CM enabled? */
>>>>>         bool scalable_mode;             /* RO - is Scalable Mode
>>>>> supported? */
>>>>> +    bool scalable_modern;           /* RO - is modern SM supported? */
>>>>>         bool snoop_control;             /* RO - is SNP filed
>>>>> supported? */
>>>>>
>>>>>         dma_addr_t root;                /* Current root table pointer */
>>>>> diff --git a/hw/i386/intel_iommu.c b/hw/i386/intel_iommu.c
>>>>> index e3465fc27d..c1382a5651 100644
>>>>> --- a/hw/i386/intel_iommu.c
>>>>> +++ b/hw/i386/intel_iommu.c
>>>>> @@ -3872,7 +3872,13 @@ static bool
>> vtd_check_hiod(IntelIOMMUState
>>>>> *s, HostIOMMUDevice *hiod,
>>>>>             return false;
>>>>>         }
>>>>>
>>>>> -    return true;
>>>>> +    if (!s->scalable_modern) {
>>>>> +        /* All checks requested by VTD non-modern mode pass */
>>>>> +        return true;
>>>>> +    }
>>>>> +
>>>>> +    error_setg(errp, "host device is unsupported in scalable modern
>>>>> mode yet");
>>>>> +    return false;
>>>>>     }
>>>>>
>>>>>     static bool vtd_dev_set_iommu_device(PCIBus *bus, void *opaque,
>>>>> int devfn,
>>>>> @@ -4262,9 +4268,9 @@ static bool
>> vtd_decide_config(IntelIOMMUState
>>>>> *s, Error **errp)
>>>>>             }
>>>>>         }
>>>>>
>>>>> -    /* Currently only address widths supported are 39 and 48 bits */
>>>>>         if ((s->aw_bits != VTD_HOST_AW_39BIT) &&
>>>>> -        (s->aw_bits != VTD_HOST_AW_48BIT)) {
>>>>> +        (s->aw_bits != VTD_HOST_AW_48BIT) &&
>>>>> +        !s->scalable_modern) {
>>>> Why does scalable_modern allow to use a value other than 39 or 48?
>>>> Is it safe?
>>> The check for scalable_modern is in patch14:
>>>
>>> if ((s->aw_bits != VTD_HOST_AW_48BIT) && s->scalable_modern) {
>>>
>>> error_setg(errp, "Supported values for aw-bits are: %d",
>>> VTD_HOST_AW_48BIT);
>>>
>>> return false;
>>>
>>> }
>>>
>>> Let me know if you prefer to move it in this patch.
>> Yes, you are right, it would be better to move the check here.
>>
>> But I think the first check should also fail even when scalable_modern
>> is enabled because values other than 39 and 48 are not supported at all,
>> whatever the mode.
>> Then, we should check if the value is valid for scalable_modern mode.
> Right, I wrote that way with a possible plan to support VTD_HOST_AW_52BIT.
52 or 57?
> What about this:
>
This condition traps (non-scalable) legacy mode as well. I think we 
should change the error message to make it clear
Something like this: "Legacy and non-modern scalable modes: supported 
values for aw-bit are ..."
Or we could make the error message conditional.
>      if ((s->aw_bits != VTD_HOST_AW_39BIT) &&
>          (s->aw_bits != VTD_HOST_AW_48BIT) &&
>          !s->scalable_modern) {
>          error_setg(errp, "Scalable legacy mode: supported values for aw-bits 
> are: %d, %d",
>                     VTD_HOST_AW_39BIT, VTD_HOST_AW_48BIT);
>          return false;
>      }
>
>      if ((s->aw_bits != VTD_HOST_AW_48BIT) && s->scalable_modern) {
>          error_setg(errp, "Scalable modern mode: supported values for aw-bits 
> is: %d",
>                     VTD_HOST_AW_48BIT);
>          return false;
>      }


>
> Thanks
> Zhenzhong