linux-kernel - Re: [PATCH 1/2] Drivers: hv: vmbus: Wait for offers during boot

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Message-ID: <12eb9ee0-b264-41f5-974e-eb564043cfcf@linux.microsoft.com>
Date: Fri, 18 Oct 2024 15:52:59 -0700
From: Easwar Hariharan <eahariha@...ux.microsoft.com>
To: Naman Jain <namjain@...ux.microsoft.com>,
 "K . Y . Srinivasan" <kys@...rosoft.com>,
 Haiyang Zhang <haiyangz@...rosoft.com>, Wei Liu <wei.liu@...nel.org>,
 Dexuan Cui <decui@...rosoft.com>
Cc: eahariha@...ux.microsoft.com, linux-hyperv@...r.kernel.org,
 linux-kernel@...r.kernel.org, John Starks <jostarks@...rosoft.com>,
 jacob.pan@...ux.microsoft.com
Subject: Re: [PATCH 1/2] Drivers: hv: vmbus: Wait for offers during boot

On 10/18/2024 4:58 AM, Naman Jain wrote:
> Channels offers are requested during vmbus initialization and resume
> from hibernation. Add support to wait for all channel offers to be
> delivered and processed before returning from vmbus_request_offers.
> This is to support user mode (VTL0) in OpenHCL (A Linux based
> paravisor for Confidential VMs) to ensure that all channel offers
> are present when init begins in VTL0, and it knows which channels
> the host has offered and which it has not.
> 
> This is in analogy to a PCI bus not returning from probe until it has
> scanned all devices on the bus.
> 
> Without this, user mode can race with vmbus initialization and miss
> channel offers. User mode has no way to work around this other than
> sleeping for a while, since there is no way to know when vmbus has
> finished processing offers.
> 
> With this added functionality, remove earlier logic which keeps track
> of count of offered channels post resume from hibernation. Once all
> offers delivered message is received, no further offers are going to
> be received. Consequently, logic to prevent suspend from happening
> after previous resume had missing offers, is also removed.
> 
> Co-developed-by: John Starks <jostarks@...rosoft.com>
> Signed-off-by: John Starks <jostarks@...rosoft.com>
> Signed-off-by: Naman Jain <namjain@...ux.microsoft.com>
> ---
>  drivers/hv/channel_mgmt.c | 38 +++++++++++++++++++++++---------------
>  drivers/hv/connection.c   |  4 ++--
>  drivers/hv/hyperv_vmbus.h | 14 +++-----------
>  drivers/hv/vmbus_drv.c    | 16 ----------------
>  4 files changed, 28 insertions(+), 44 deletions(-)

Looks good to me.

Reviewed-by: Easwar Hariharan <eahariha@...ux.microsoft.com>