Re: [virtio-comment] [PATCH v4 1/3] content: Document balloon feature page poison

[David Hildenbrand <david@redhat.com>]

On 27.05.20 06:06, Alexander Duyck wrote:
> From: Alexander Duyck <alexander.h.duyck@linux.intel.com>
> 
> Page poison provides a way for the guest to notify the host that it is
> initializing or poisoning freed pages with some specific poison value. As a
> result of this we can infer a couple traits about the guest:
> 
> 1. Free pages will contain a specific pattern within the guest.
> 2. Modifying free pages from this value may cause an error in the guest.
> 3. Pages will be immediately written to by the driver when deflated.
> 
> There are currently no existing features that make use of this data. In the
> upcoming feature free page reporting we will need to make use of this to
> identify if we can evict pages from the guest without causing data
> corruption.
> 
> Add documentation for the page poison feature describing the basic
> functionality and requirements.
> 
> Signed-off-by: Alexander Duyck <alexander.h.duyck@linux.intel.com>
> ---
>  conformance.tex |    2 ++
>  content.tex     |   59 +++++++++++++++++++++++++++++++++++++++++++++++++++----
>  2 files changed, 57 insertions(+), 4 deletions(-)
> 
> diff --git a/conformance.tex b/conformance.tex
> index b6fdec090383..4ed9d62e8088 100644
> --- a/conformance.tex
> +++ b/conformance.tex
> @@ -149,6 +149,7 @@ \section{Conformance Targets}\label{sec:Conformance / Conformance Targets}
>  \item \ref{drivernormative:Device Types / Memory Balloon Device / Feature bits}
>  \item \ref{drivernormative:Device Types / Memory Balloon Device / Device Operation}
>  \item \ref{drivernormative:Device Types / Memory Balloon Device / Device Operation / Memory Statistics}
> +\item \ref{drivernormative:Device Types / Memory Balloon Device / Device Operation / Page Poison}
>  \end{itemize}
>  
>  \conformance{\subsection}{SCSI Host Driver Conformance}\label{sec:Conformance / Driver Conformance / SCSI Host Driver Conformance}
> @@ -331,6 +332,7 @@ \section{Conformance Targets}\label{sec:Conformance / Conformance Targets}
>  \item \ref{devicenormative:Device Types / Memory Balloon Device / Feature bits}
>  \item \ref{devicenormative:Device Types / Memory Balloon Device / Device Operation}
>  \item \ref{devicenormative:Device Types / Memory Balloon Device / Device Operation / Memory Statistics}
> +\item \ref{devicenormative:Device Types / Memory Balloon Device / Device Operation / Page Poison}
>  \end{itemize}
>  
>  \conformance{\subsection}{SCSI Host Device Conformance}\label{sec:Conformance / Device Conformance / SCSI Host Device Conformance}
> diff --git a/content.tex b/content.tex
> index 91735e3eb018..4a0ab90260ff 100644
> --- a/content.tex
> +++ b/content.tex
> @@ -5019,6 +5019,9 @@ \subsection{Feature bits}\label{sec:Device Types / Memory Balloon Device / Featu
>      memory statistics is present.
>  \item[VIRTIO_BALLOON_F_DEFLATE_ON_OOM (2) ] Deflate balloon on
>      guest out of memory condition.
> +\item[ VIRTIO_BALLOON_F_PAGE_POISON(4) ] A hint to the device, that the driver
> +    will immediately write \field{poison_val} to pages after deflating them.
> +    Configuration field \field{poison_val} is valid.
>  

Here we have "that the driver will immediately" ...

But we never document that in form of a normative statement (e.g., "The
driver MUST initialize pages with \field{poison_val} after deflating").

Just wondering if that is intended (I imagine it will be different with
free page reporting)?

Apart from that looks good to me!

-- 
Thanks,

David / dhildenb