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Re: [PATCH V4 08/13] hyperv/vmbus: Initialize VMbus ring buffer for Isolation VM

On 9/2/2021 8:23 AM, Michael Kelley wrote:
+       } else {
+               pages_wraparound = kcalloc(page_cnt * 2 - 1,
+                                          sizeof(struct page *),
+                                          GFP_KERNEL);
+               pages_wraparound[0] = pages;
+               for (i = 0; i < 2 * (page_cnt - 1); i++)
+                       pages_wraparound[i + 1] =
+                               &pages[i % (page_cnt - 1) + 1];
+               ring_info->ring_buffer = (struct hv_ring_buffer *)
+                       vmap(pages_wraparound, page_cnt * 2 - 1, VM_MAP,
+                               PAGE_KERNEL);
+               kfree(pages_wraparound);
+               if (!ring_info->ring_buffer)
+                       return -ENOMEM;
+       }
With this patch, the code is a big "if" statement with two halves -- one
when SNP isolation is in effect, and the other when not.  The SNP isolation
case does the work using PFNs with the shared_gpa_boundary added,
while the other case does the same work but using struct page.  Perhaps
I'm missing something, but can both halves be combined and always
do the work using PFNs?  The only difference is whether to add the
shared_gpa_boundary, and whether to zero the memory when done.
So get the starting PFN, then have an "if" statement for whether to
add the shared_gpa_boundary.  Then everything else is the same.
At the end, use an "if" statement to decide whether to zero the
memory.  It would really be better to have the logic in this algorithm
coded only once.

Hi Michael:
I have tried this before. But vmap_pfn() only works for those pfns out of normal memory. Please see vmap_pfn_apply() for detail and
return error when the PFN is valid.



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