Re: [PATCH V3 12/13] HV/Netvsc: Add Isolation VM support for netvsc driver

[Tom Lendacky <thomas.lendacky@xxxxxxx>]

On 8/19/21 11:21 PM, hch@xxxxxx wrote:
> On Thu, Aug 19, 2021 at 06:14:51PM +0000, Michael Kelley wrote:
> > > +       if (!pfns)
> > > +               return NULL;
> > > +
> > > +       for (i = 0; i < size / HV_HYP_PAGE_SIZE; i++)
> > > +               pfns[i] = virt_to_hvpfn(buf + i * HV_HYP_PAGE_SIZE)
> > > +                       + (ms_hyperv.shared_gpa_boundary >> HV_HYP_PAGE_SHIFT);
> > > +
> > > +       vaddr = vmap_pfn(pfns, size / HV_HYP_PAGE_SIZE, PAGE_KERNEL_IO);
> > > +       kfree(pfns);
> > > +
> > > +       return vaddr;
> > > +}
> > This function appears to be a duplicate of hv_map_memory() in Patch 11 of this
> > series.  Is it possible to structure things so there is only one 
> > implementation?  In
> So right now it it identical, but there is an important difference:
> the swiotlb memory is physically contiguous to start with, so we can
> do the simple remap using vmap_range as suggested in the last mail.
> The cases here are pretty weird in that netvsc_remap_buf is called right
> after vzalloc.  That is we create _two_ mappings in vmalloc space right
> after another, where the original one is just used for establishing the
> "GPADL handle" and freeing the memory.  In other words, the obvious thing
> to do here would be to use a vmalloc variant that allows to take the
> shared_gpa_boundary into account when setting up the PTEs.
>
> And here is somthing I need help from the x86 experts:  does the CPU
> actually care about this shared_gpa_boundary?  Or does it just matter
> for the generated DMA address?  Does somehow have a good pointer to
> how this mechanism works?
The CPU does care. Here's some info:

APM Volume 2, Section 15.36.8:
https://www.amd.com/system/files/TechDocs/24593.pdf

AMD SEV-SNP Whitepaper, Virtual Machine Privilege Levels (~page 14):
https://www.amd.com/system/files/TechDocs/SEV-SNP-strengthening-vm-isolation-with-integrity-protection-and-more.pdf

Thanks,
Tom

>