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

[CLEMENT MATHIEU--DRIF]

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?
>           error_setg(errp, "Supported values for aw-bits are: %d, %d",
>                      VTD_HOST_AW_39BIT, VTD_HOST_AW_48BIT);
>           return false;
> --
> 2.34.1
>