Re: [PATCH v1 17/22] intel_iommu: do not pass down pasid bind for PASID #0

[Peter Xu <peterx@redhat.com>]

On Sun, Mar 22, 2020 at 05:36:14AM -0700, Liu Yi L wrote:
> RID_PASID field was introduced in VT-d 3.0 spec, it is used
> for DMA requests w/o PASID in scalable mode VT-d. It is also
> known as IOVA. And in VT-d 3.1 spec, there is definition on it:
> 
> "Implementations not supporting RID_PASID capability
> (ECAP_REG.RPS is 0b), use a PASID value of 0 to perform
> address translation for requests without PASID."
> 
> This patch adds a check against the PASIDs which are going to be
> bound to device. For PASID #0, it is not necessary to pass down
> pasid bind request for it since PASID #0 is used as RID_PASID for
> DMA requests without pasid. Further reason is current Intel vIOMMU
> supports gIOVA by shadowing guest 2nd level page table. However,
> in future, if guest IOMMU driver uses 1st level page table to store
> IOVA mappings, then guest IOVA support will also be done via nested
> translation. When gIOVA is over FLPT, then vIOMMU should pass down
> the pasid bind request for PASID #0 to host, host needs to bind the
> guest IOVA page table to a proper PASID. e.g PASID value in RID_PASID
> field for PF/VF if ECAP_REG.RPS is clear or default PASID for ADI
> (Assignable Device Interface in Scalable IOV solution).
> 
> IOVA over FLPT support on Intel VT-d:
> https://lkml.org/lkml/2019/9/23/297
> 
> Cc: Kevin Tian <kevin.tian@intel.com>
> Cc: Jacob Pan <jacob.jun.pan@linux.intel.com>
> Cc: Peter Xu <peterx@redhat.com>
> Cc: Yi Sun <yi.y.sun@linux.intel.com>
> Cc: Paolo Bonzini <pbonzini@redhat.com>
> Cc: Richard Henderson <rth@twiddle.net>
> Cc: Eduardo Habkost <ehabkost@redhat.com>
> Signed-off-by: Liu Yi L <yi.l.liu@intel.com>
> ---
>  hw/i386/intel_iommu.c | 10 ++++++++++
>  1 file changed, 10 insertions(+)
> 
> diff --git a/hw/i386/intel_iommu.c b/hw/i386/intel_iommu.c
> index 1e0ccde..b007715 100644
> --- a/hw/i386/intel_iommu.c
> +++ b/hw/i386/intel_iommu.c
> @@ -1886,6 +1886,16 @@ static int vtd_bind_guest_pasid(IntelIOMMUState *s, VTDBus *vtd_bus,
>      struct iommu_gpasid_bind_data *g_bind_data;
>      int ret = -1;
>  
> +    if (pasid < VTD_MIN_HPASID) {
> +        /*
> +         * If pasid < VTD_HPASID_MIN, this pasid is not allocated

s/VTD_HPASID_MIN/VTD_MIN_HPASID/.

> +         * from host. No need to pass down the changes on it to host.
> +         * TODO: when IOVA over FLPT is ready, this switch should be
> +         * refined.

What will happen if without this patch?  Is it a must?

> +         */
> +        return 0;
> +    }
> +
>      vtd_dev_icx = vtd_bus->dev_icx[devfn];
>      if (!vtd_dev_icx) {
>          return -EINVAL;
> -- 
> 2.7.4
> 

-- 
Peter Xu