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

[CLEMENT MATHIEU--DRIF]

On 13/08/2024 08:26, 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 13/08/2024 04:20, Duan, Zhenzhong wrote:
>>> Caution: External email. Do not open attachments or click links, unless this
>> email comes from a known sender and you know the content is safe.
>>>
>>>> -----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:
>>>>> Caution: External email. Do not open attachments or click links,
>>>>> unless this email comes from a known sender and you know the content
>>>>> is safe.
>>>>>
>>>>>
>>>>> 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,
>>>>>>> unless this email comes from a known sender and you know the
>> content
>>>>>>> is safe.
>>>>>>>
>>>>>>>
>>>>>>> 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?
> Sorry, I mean 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.
> Yes, I'd like to be conditional, like:
>
>      if ((s->aw_bits != VTD_HOST_AW_39BIT) &&
>          (s->aw_bits != VTD_HOST_AW_48BIT) &&
>          !s->scalable_modern) {
>          error_setg(errp, "%s mode: supported values for aw-bits are: %d, %d",
>                     s->scalable_mode ? "Scalable legacy" : "Legacy",
>                     VTD_HOST_AW_39BIT, VTD_HOST_AW_48BIT);
>          return false;
>      }
Fine,
lgtm

 >cmd
>>>       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