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Subject: Re: [PATCH v5 1/3] content: Document balloon feature page poison
On Mon, 06 Jul 2020 14:18:22 -0700 Alexander Duyck <alexander.duyck@gmail.com> 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(-) (...) > @@ -5042,13 +5049,17 @@ \subsection{Feature bits}\label{sec:Device Types / Memory Balloon Device / Featu > VIRTIO_BALLOON_F_MUST_TELL_HOST is not negotiated. > > \subsection{Device configuration layout}\label{sec:Device Types / Memory Balloon Device / Device configuration layout} > - Both fields of this configuration > - are always available. > + \field{num_pages} and \field{actual} are always available. > + > + \field{poison_val} is available if VIRTIO_BALLOON_F_PAGE_POISON has been > + negotiated. > > \begin{lstlisting} > struct virtio_balloon_config { > le32 num_pages; > le32 actual; > + le32 free_page_hint_cmd_id; This is slightly confusing, as free page hinting is only introduced in a later patch; maybe call this 'reserved' and rename in the patch introducing page hinting? But no real need to do so, I just stumbled over it. > + le32 poison_val; > }; > \end{lstlisting} > > @@ -5072,9 +5083,15 @@ \subsection{Device Initialization}\label{sec:Device Types / Memory Balloon Devic > \begin{enumerate} > \item Identify the stats virtqueue. > \item Add one empty buffer to the stats virtqueue. > - \item DRIVER_OK is set: device operation begins. > - \item Notify the device about the stats virtqueue buffer. > \end{enumerate} > + > +\item If the VIRTIO_BALLOON_F_PAGE_POISON feature bit is negotiated, the > + driver updates the \field{poison_val} configuration field. s/the driver updates/update/ would be more in line with the other wording here; more of a nit, feel free to keep as-is. > + > +\item DRIVER_OK is set: device operation begins. > + > +\item If the VIRTIO_BALLOON_F_STATS_VQ feature bit is negotiated, then > + notify the device about the stats virtqueue buffer. > \end{enumerate} > > \subsection{Device Operation}\label{sec:Device Types / Memory Balloon Device / Device Operation} > @@ -5345,6 +5362,40 @@ \subsubsection{Memory Statistics Tags}\label{sec:Device Types / Memory Balloon D > allocations in the guest. > \end{description} > > +\subsubsection{Page Poison}\label{sec:Device Types / Memory Balloon Device / Device Operation / Page Poison} > + > +Page Poison provides a way to notify the host that the guest is initializing > +free pages with \field{poison_val}. When the feature is enabled, pages will > +be immediately written to by the driver after deflating. > + > +If the guest is not initializing freed pages the driver should reject the s/pages/pages,/ > +VIRTIO_BALLOON_F_PAGE_POISON feature. > + > +If VIRTIO_BALLOON_F_PAGE_POISON feature has been negotiated, the driver > +will place the initialization value into the \field{poison_val} > +configuration field data. > + > +\drivernormative{\paragraph}{Page Poison}{Device Types / Memory Balloon Device / Device Operation / Page Poison} > + > +Normative statements in this section apply if the > +VIRTIO_BALLOON_F_PAGE_POISON feature has been negotiated. > + > +The driver MUST initialize the deflated pages with \field{poison_val} when > +they are reused by the driver. > + > +The driver MUST populate the \field{poison_val} configuration data before > +setting the DRIVER_OK bit. > + > +The driver MUST NOT modify \field{poison_val} while the DRIVER_OK bit is set. > + > +\devicenormative{\paragraph}{Page Poison}{Device Types / Memory Balloon Device / Device Operation / Page Poison} > + > +Normative statements in this section apply if the > +VIRTIO_BALLOON_F_PAGE_POISON feature has been negotiated. > + > +The device MAY use the content of \field{poison_val} as a hint to guest > +behavior. > + > \section{SCSI Host Device}\label{sec:Device Types / SCSI Host Device} > > The virtio SCSI host device groups together one or more virtual > > Just some nits, otherwise Reviewed-by: Cornelia Huck <cohuck@redhat.com>
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