linux-kernel - Re: [PATCH] Revert "xen/balloon: Mark unallocated host memory as UNUSABLE"

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Date:   Tue, 27 Nov 2018 17:42:45 -0500
From:   Boris Ostrovsky <boris.ostrovsky@...cle.com>
To:     Igor Druzhinin <igor.druzhinin@...rix.com>,
        xen-devel@...ts.xenproject.org, linux-kernel@...r.kernel.org
Cc:     jgross@...e.com, jbeulich@...e.com
Subject: Re: [PATCH] Revert "xen/balloon: Mark unallocated host memory as
 UNUSABLE"

On 11/27/18 3:58 PM, Igor Druzhinin wrote:
> This reverts commit b3cf8528bb21febb650a7ecbf080d0647be40b9f.
>
> That commit unintentionally broke Xen balloon memory hotplug with
> "hotplug_unpopulated" set to 1. As long as "System RAM" resource
> got assigned under a new "Unusable memory" resource in IO/Mem tree
> any attempt to online this memory would fail due to general kernel
> restrictions on having "System RAM" resources as 1st level only.
>
> The original issue that commit has tried to workaround fa564ad96366
> ("x86/PCI: Enable a 64bit BAR on AMD Family 15h (Models 00-1f, 30-3f,
> 60-7f)") also got amended by the following 03a551734 ("x86/PCI: Move
> and shrink AMD 64-bit window to avoid conflict") which made the
> original fix to Xen ballooning unnecessary.
>
> Signed-off-by: Igor Druzhinin <igor.druzhinin@...rix.com>
> ---
> In mail thread [1] it was agreed to revert the change due to technical
> comlications of fixing it and the fact that there is no any strong reason
> to keep it.
>
> [1] https://lists.xenproject.org/archives/html/xen-devel/2018-11/msg02834.html
> ---
>  arch/x86/xen/enlighten.c | 78 ------------------------------------------------
>  arch/x86/xen/setup.c     |  6 ++--
>  drivers/xen/balloon.c    | 65 ++++++----------------------------------
>  include/xen/balloon.h    |  5 ----
>  4 files changed, 13 insertions(+), 141 deletions(-)


Reviewed-by: Boris Ostrovsky <boris.ostrovsky@...cle.com>