Re: [PATCH V6 3/5] hyper-v: Enable swiotlb bounce buffer for Isolation VM

[Tianyu Lan <ltykernel@gmail.com>]

On 12/10/2021 9:25 PM, Tianyu Lan wrote:
>>> @@ -319,8 +320,16 @@ static void __init ms_hyperv_init_platform(void)
>>>           pr_info("Hyper-V: Isolation Config: Group A 0x%x, Group B 
>>> 0x%x\n",
>>>               ms_hyperv.isolation_config_a, 
>>> ms_hyperv.isolation_config_b);
>>>
>>> -        if (hv_get_isolation_type() == HV_ISOLATION_TYPE_SNP)
>>> +        if (hv_get_isolation_type() == HV_ISOLATION_TYPE_SNP) {
>>>               static_branch_enable(&isolation_type_snp);
>>> +            swiotlb_unencrypted_base = ms_hyperv.shared_gpa_boundary;
>>> +        }
>>> +
>>> +        /*
>>> +         * Enable swiotlb force mode in Isolation VM to
>>> +         * use swiotlb bounce buffer for dma transaction.
>>> +         */
>>> +        swiotlb_force = SWIOTLB_FORCE;
>> I'm good with this approach that directly updates the swiotlb settings 
>> here
>>
>> rather than in IOMMU initialization code.  It's a lot more 
>> straightforward.
>>
>> However, there's an issue if building for X86_32 without PAE, in that the
>> swiotlb module may not be built, resulting in compile and link 
>> errors.  The
>> swiotlb.h file needs to be updated to provide a stub function for
>> swiotlb_update_mem_attributes().   swiotlb_unencrypted_base probably
>> needs wrapper functions to get/set it, which can be stubs when
>> CONFIG_SWIOTLB is not set.  swiotlb_force is a bit of a mess in that 
>> it already
>> has a stub definition that assumes it will only be read, and not set.  
>> A bit of
>> thinking will be needed to sort that out.
> 
> It's ok to fix the issue via selecting swiotlb when CONFIG_HYPERV is
> set?
> 
Sorry. ignore the previous statement. These codes doesn't depend on 
CONFIG_HYPERV.

How about making these code under #ifdef CONFIG_X86_64 or CONFIG_SWIOTLB?