netdev - Re: [PATCH V3 08/13] HV/Vmbus: Initialize VMbus ring buffer for Isolation VM

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Date:   Tue, 17 Aug 2021 23:36:22 +0800
From:   Tianyu Lan <ltykernel@...il.com>
To:     Michael Kelley <mikelley@...rosoft.com>,
        KY Srinivasan <kys@...rosoft.com>,
        Haiyang Zhang <haiyangz@...rosoft.com>,
        Stephen Hemminger <sthemmin@...rosoft.com>,
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Subject: Re: [PATCH V3 08/13] HV/Vmbus: Initialize VMbus ring buffer for
 Isolation VM



On 8/17/2021 1:28 AM, Michael Kelley wrote:
> This patch does the following:
> 
> 1) The existing ring buffer wrap-around mapping functionality is still
> executed in hv_ringbuffer_init() when not doing SNP isolation.
> This mapping is based on an array of struct page's that describe the
> contiguous physical memory.
> 
> 2) New ring buffer wrap-around mapping functionality is added in
> hv_ringbuffer_post_init() for the SNP isolation case.  The case is
> handled in hv_ringbuffer_post_init() because it must be done after
> the GPADL is established, since that's where the host visibility
> is set.  What's interesting is that this case is exactly the same
> as #1 above, except that the mapping is based on physical
> memory addresses instead of struct page's.  We have to use physical
> addresses because of applying the GPA boundary, and there are no
> struct page's for those physical addresses.
> 
> Unfortunately, this duplicates a lot of logic in #1 and #2, except
> for the struct page vs. physical address difference.
> 
> Proposal:  Couldn't we always do #2, even for the normal case
> where SNP isolation is not being used?   The difference would
> only be in whether the GPA boundary is added.  And it looks like
> the normal case could be done after the GPADL is established,
> as setting up the GPADL doesn't have any dependencies on
> having the ring buffer mapped.  This approach would remove
> a lot of duplication.  Just move the calls to hv_ringbuffer_init()
> to after the GPADL is established, and do all the work there for
> both cases.
> 

Hi Michael:
     Thanks for suggestion. I just keep the original logic in current
code. I will try combining these two functions and report back.

Thanks.