RE: [PATCH v3 03/11] Drivers: hv: vmbus: Introduce types of GPADL

[Michael Kelley <mikelley@microsoft.com>]

From: Boqun Feng <boqun.feng@gmail.com> Sent: Thursday, September 10, 2020 7:35 AM

> 
> This patch introduces two types of GPADL: HV_GPADL_{BUFFER, RING}. The
> types of GPADL are purely the concept in the guest, IOW the hypervisor
> treat them as the same.
> 
> The reason of introducing the types for GPADL is to support guests whose
> page size is not 4k (the page size of Hyper-V hypervisor). In these
> guests, both the headers and the data parts of the ringbuffers need to
> be aligned to the PAGE_SIZE, because 1) some of the ringbuffers will be
> mapped into userspace and 2) we use "double mapping" mechanism to
> support fast wrap-around, and "double mapping" relies on ringbuffers
> being page-aligned. However, the Hyper-V hypervisor only uses 4k
> (HV_HYP_PAGE_SIZE) headers. Our solution to this is that we always make
> the headers of ringbuffers take one guest page and when GPADL is
> established between the guest and hypervisor, the only first 4k of
> header is used. To handle this special case, we need the types of GPADL
> to differ different guest memory usage for GPADL.
> 
> Type enum is introduced along with several general interfaces to
> describe the differences between normal buffer GPADL and ringbuffer
> GPADL.
> 
> Signed-off-by: Boqun Feng <boqun.feng@gmail.com>
> ---
>  drivers/hv/channel.c   | 160 +++++++++++++++++++++++++++++++++++------
>  include/linux/hyperv.h |  44 +++++++++++-
>  2 files changed, 183 insertions(+), 21 deletions(-)
> 

Reviewed-by: Michael Kelley <mikelley@microsoft.com>