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 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.
What about this:

    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