Re: [PATCH for-stable-5.10.y] xen-blkfront: Cache feature_persistent value before advertisement

[Greg KH <gregkh@xxxxxxxxxxxxxxxxxxx>]

On Tue, Sep 06, 2022 at 04:24:14PM +0000, SeongJae Park wrote:
> commit fe8f65b018effbf473f53af3538d0c1878b8b329 upstream.
> 
> Xen blkfront advertises its support of the persistent grants feature
> when it first setting up and when resuming in 'talk_to_blkback()'.
> Then, blkback reads the advertised value when it connects with blkfront
> and decides if it will use the persistent grants feature or not, and
> advertises its decision to blkfront.  Blkfront reads the blkback's
> decision and it also makes the decision for the use of the feature.
> 
> Commit 402c43ea6b34 ("xen-blkfront: Apply 'feature_persistent' parameter
> when connect"), however, made the blkfront's read of the parameter for
> disabling the advertisement, namely 'feature_persistent', to be done
> when it negotiate, not when advertise.  Therefore blkfront advertises
> without reading the parameter.  As the field for caching the parameter
> value is zero-initialized, it always advertises as the feature is
> disabled, so that the persistent grants feature becomes always disabled.
> 
> This commit fixes the issue by making the blkfront does parmeter caching
> just before the advertisement.
> 
> Fixes: 402c43ea6b34 ("xen-blkfront: Apply 'feature_persistent' parameter when 
> connect")
> Cc: <stable@xxxxxxxxxxxxxxx> # 5.10.x
> Reported-by: Marek Marczykowski-Górecki <marmarek@xxxxxxxxxxxxxxxxxxxxxx>
> Signed-off-by: SeongJae Park <sj@xxxxxxxxxx>
> Tested-by: Marek Marczykowski-Górecki <marmarek@xxxxxxxxxxxxxxxxxxxxxx>
> Reviewed-by: Juergen Gross <jgross@xxxxxxxx>
> Link: https://lore.kernel.org/r/20220831165824.94815-4-sj@xxxxxxxxxx
> Signed-off-by: Juergen Gross <jgross@xxxxxxxx>
> ---
> 
> This patch is a manual backport of the upstream commit on the 5.10.y
> kernel.  Please note that this patch can be applied on the latest 5.10.y
> only after the preceding patch[1] is applied.
> 
> [1] 
> https://lore.kernel.org/stable/20220906132819.016040100@xxxxxxxxxxxxxxxxxxx/

Now queued up, thanks.

greg k-h