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docs/features/dom0less: Update the late XenStore init protocol
With the new allocation strategy of Dom0less DomUs XenStore page, update the doc of the late XenStore init protocol accordingly. Signed-off-by: Henry Wang <xin.wang2@amd.com> Signed-off-by: Stefano Stabellini <stefano.stabellini@amd.com> Reviewed-by: Michal Orzel <michal.orzel@amd.com>
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Henry Wang authored and Stefano Stabellini committed
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@@ -110,9 +110,10 @@ hotplug PV drivers to dom0less guests. E.g. xl network-attach domU.
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The implementation works as follows:
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- Xen allocates the xenstore event channel for each dom0less domU that
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has the "xen,enhanced" property, and sets HVM_PARAM_STORE_EVTCHN
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- Xen does *not* allocate the xenstore page and sets HVM_PARAM_STORE_PFN
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to ~0ULL (invalid)
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- Dom0less domU kernels check that HVM_PARAM_STORE_PFN is set to invalid
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- Xen allocates the xenstore page and sets HVM_PARAM_STORE_PFN as well
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as the connection status to XENSTORE_RECONNECT.
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- Dom0less domU kernels check that HVM_PARAM_STORE_PFN is set to
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~0ULL (invalid) or the connection status is *not* XENSTORE_CONNECTED.
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- Old kernels will continue without xenstore support (Note: some old
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buggy kernels might crash because they don't check the validity of
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HVM_PARAM_STORE_PFN before using it! Disable "xen,enhanced" in
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@@ -121,13 +122,14 @@ The implementation works as follows:
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channel (HVM_PARAM_STORE_EVTCHN) before continuing with the
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initialization
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- Once dom0 is booted, init-dom0less is executed:
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- it allocates the xenstore shared page and sets HVM_PARAM_STORE_PFN
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- it gets the xenstore shared page from HVM_PARAM_STORE_PFN
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- it calls xs_introduce_domain
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- Xenstored notices the new domain, initializes interfaces as usual, and
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sends an event channel notification to the domain using the xenstore
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event channel (HVM_PARAM_STORE_EVTCHN)
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- The Linux domU kernel receives the event channel notification, checks
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HVM_PARAM_STORE_PFN again and continue with the initialization
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HVM_PARAM_STORE_PFN and the connection status again and continue with
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the initialization
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Limitations
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