Re: [Xen-devel] [PATCH 2/3] amd-iommu: disable iommu_hap_pt_share with AMD IOMMUs

[Roger Pau Monné <roger.pau@xxxxxxxxxx>]

On 08/04/14 10:52, Jan Beulich wrote:
>>>> On 07.04.14 at 18:02, <roger.pau@xxxxxxxxxx> wrote:
>> --- a/xen/drivers/passthrough/amd/iommu_init.c
>> +++ b/xen/drivers/passthrough/amd/iommu_init.c
>> @@ -1255,6 +1255,13 @@ int __init amd_iommu_init(void)
>>      if ( iterate_ivrs_mappings(amd_iommu_setup_device_table) != 0 )
>>          goto error_out;
>>  
>> +    /*
>> +     * Disable sharing HAP page tables with AMD IOMMU,
>> +     * since it only supports p2m_ram_rw, and this would
>> +     * prevent doing IO to/from mapped grant frames.
>> +     */
>> +    iommu_hap_pt_share = 0;
>> +
> 
> I guess at the very least when the option was specified on the
> command line you should issue a warning, or perhaps even stay
> away from enforcing this.

I think we should enforce it even if the user has specified
sharept=true, or else we need to gate the
XENFEAT_hvm_gntmap_supports_iommu feature. Printing a Warning in this
case (user trying to enforce sharept on AMD IOMMU) seems OK to me.

Roger.


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