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

[Duan, Zhenzhong]

>-----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
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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:
>>>> 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;
    }

>>      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