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

[CLEMENT MATHIEU--DRIF]

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:
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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.

Thanks
 >cmd
>
> Thanks
>
> Zhenzhong
>