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