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Subject: Re: [virtio-comment] [PATCH v3 2/3] content: Document balloon feature page poison
On 20.05.20 04:02, Alexander Duyck wrote: > From: Alexander Duyck <alexander.h.duyck@linux.intel.com> > > Page poison provides a way for the guest to notify the host of the content > expected to be found in pages when they are added back to the guest after > being discarded. The feature currently doesn't apply to the existing > balloon features, however it will apply to an upcoming feature, free page > reporting. Add documentation for the page poison feature describing the > basic functionality and requirements. > I would rephrase this, starting what it does *without* free page reporting (which is not "provides a way for the guest to notify ..."), and then eventually how this feature will also be used in the future as well with free page reporting. > Signed-off-by: Alexander Duyck <alexander.h.duyck@linux.intel.com> > --- > conformance.tex | 2 ++ > content.tex | 44 ++++++++++++++++++++++++++++++++++++++++++++ > 2 files changed, 46 insertions(+) > > diff --git a/conformance.tex b/conformance.tex > index a14e26edfcb2..5038b36324ac 100644 > --- a/conformance.tex > +++ b/conformance.tex > @@ -150,6 +150,7 @@ \section{Conformance Targets}\label{sec:Conformance / Conformance Targets} > \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 / Free Page Hinting} > +\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} > @@ -333,6 +334,7 @@ \section{Conformance Targets}\label{sec:Conformance / Conformance Targets} > \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 / Free Page Hinting} > +\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 816b6c1b052e..89e9948b7399 100644 > --- a/content.tex > +++ b/content.tex > @@ -5026,6 +5026,9 @@ \subsection{Feature bits}\label{sec:Device Types / Memory Balloon Device / Featu > page hinting. A virtqueue for providing hints as to what memory is > currently free is present. Configuration field \field{free_page_hint_cmd_id} > is valid. > +\item[ VIRTIO_BALLOON_F_PAGE_POISON(4) ] The device has to be notified if > + the driver is expecting balloon pages to contain a certain value when > + returned. Configuration field poison_val is valid. That's not what it does in the context of this feature only, no? "A hint to the device, that the driver might immediately write \field{poison_val} to pages after deflating them. Configuration field \field{poison_val} is valid." > > \end{description} > > @@ -5033,6 +5036,9 @@ \subsection{Feature bits}\label{sec:Device Types / Memory Balloon Device / Featu > The driver SHOULD accept the VIRTIO_BALLOON_F_MUST_TELL_HOST > feature if offered by the device. > > +The driver SHOULD clear the VIRTIO_BALLOON_F_PAGE_POISON flag if it is not > +expecting any specific value to be stored in the page. That's not what it does in the context of this feature only, no? "The driver SHOULD clear the VIRTIO_BALLOON_F_PAGE_POISON flag if it is not immediately write \field{poison_val} to deflated pages (e.g., to initialize them, or fill them with a poison value)." ? > + > \devicenormative{\subsubsection}{Feature bits}{Device Types / Memory Balloon Device / Feature bits} > If the device offers the VIRTIO_BALLOON_F_MUST_TELL_HOST feature > bit, and if the driver did not accept this feature bit, the > @@ -5055,11 +5061,15 @@ \subsection{Device configuration layout}\label{sec:Device Types / Memory Balloon > VIRTIO_BALLOON_F_FREE_PAGE_HINT has been negotiated and is read-only by > the driver. > > + \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; > + le32 poison_val; > }; > \end{lstlisting} > > @@ -5088,6 +5098,9 @@ \subsection{Device Initialization}\label{sec:Device Types / Memory Balloon Devic > \item If the VIRTIO_BALLOON_F_FREE_PAGE_HINT feature bit is negotiated, the > free_page_vq is identified. > > +\item If the VIRTIO_BALLOON_F_PAGE_POISON feature bit is negotiated, the > + driver updates the \field{poison_val} configuration field. > + > \item DRIVER_OK is set: device operation begins. > > \item If the VIRTIO_BALLOON_F_STATS_VQ feature bit is negotiated, then > @@ -5473,6 +5486,37 @@ \subsubsection{Free Page Hinting}\label{sec:Device Types / Memory Balloon Device > \field{free_page_hint_cmd_id} once it no longer has need for the > previously hinted pages. > > +\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 > +and/or poisoning free pages. When the feature is enabled pages that are s/enabled/enabled, / > +deflated might be immediately written to by the guest. "pages might immediately get written to by the driver after deflating." ? > + > +If the guest is not initializing or poisoning freed pages it should reject Sometimes you use "write to pages after deflating", here you use "freed pages" > +the VIRTIO_BALLOON_F_PAGE_POISON feature. > + > +If VIRTIO_BALLOON_F_PAGE_POISON feature has been negotiated, the guest > +will place the expected poison value into the \field{poison_val} again, "expected" is misleading in the context of this patch only. > +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 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. -- Thanks, David / dhildenb
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