On 08.05.20 19:16, Alexander Duyck wrote:
> From: Alexander Duyck <[email protected]>
>
> 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.
>
> Signed-off-by: Alexander Duyck <[email protected]>
> ---
> content.tex | 45 +++++++++++++++++++++++++++++++++++++++++++++
> 1 file changed, 45 insertions(+)
>
> diff --git a/content.tex b/content.tex
> index 7d91604178fd..e154948a9a1a 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 free_page_hint_cmd_id
> is valid.
> +\item[ VIRTIO_BALLOON_F_PAGE_POISON(4) ] Host has to be notified if guest
> + is expecting reported pages to contain a certain value when returned.
> + Configuration 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.
> +
> \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 then
> + the driver MUST update the 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
> @@ -5461,6 +5474,38 @@ \subsubsection{Free Page Hinting}\label{sec:Device
> Types / Memory Balloon Device
> The device MAY NOT modify the contents of the balloon after
> \field{free_page_hint_cmd_id} is set to VIRTIO_BALLOON_CMD_ID_DONE.
>
> +\subsubsection{Page Poison}\label{sec:Device Types / Memory Balloon Device /
> Device Operation / Page Poison}
> +
> +Page Poison provides a way to notify the host of the contents that are
> +currently in the balloon pages, and those that are expected to be in the
> +pages when they are pulled from the balloon. It is used for in-place
"when they are pulled from the balloon". That's not correct. This only
applies to free page reporting (-> patch #3).
Without free page reporting, poisoning only tells the hypervisor that
pages pages that are getting deflated might immediately be written by
the hypervisor again.
Or am I missing something?
> +reporting of pages without needing to pull them from the memory allocator
> +of the guest.
> +
> +If VIRTIO_BALLOON_F_PAGE_POISON feature has been negotiated, the guest
> +will place the expected poison value in \field{poison_val} configuration
> +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 if it is
> +expecting the page to contain some fixed value when free.
Again, not correctly phrased I think. Only applies to free page reporting.
> +
> +The driver MAY opt to disable the feature if it will take care of
> +re-initializing pages when first accessing them.
> +
> +\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 ignore the \field{poison_val} for normal balloon operations
> and
> +free page hinting as this feature did not exist prior to those features being
> +added.
The device can always ignore this field without free page reporting.
It's only a hint that the guest is using poisoning, nothing else.
--
Thanks,
David / dhildenb
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