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

[Tianyu Lan]

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?