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