Re: [Xen-devel] [PATCH for-4.10.0-shim-comet] x86/guest: use the vcpu_info area from shared_info

[George Dunlap <george.dunlap@xxxxxxxxxx>]

On 01/17/2018 10:57 AM, Roger Pau Monne wrote:
> If using less than 32 vCPUs (XEN_LEGACY_MAX_VCPUS).
> 
> This is a workaround that should allow to boot the shim on hypervisors
> without commit "x86/upcall: inject a spurious event after setting
> upcall vector" as long as less than 32 vCPUs are assigned to the
> shim.
> 
> Signed-off-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>
> ---
> Cc: Jan Beulich <jbeulich@xxxxxxxx>
> Cc: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
> Cc: Wei Liu <wei.liu2@xxxxxxxxxx>
> Cc: Ian Jackson <ian.jackson@xxxxxxxxxxxxx>
> Cc: George Dunlap <george.dunlap@xxxxxxxxxx>
> ---
> ONLY apply to the 4.10.0-shim-comet branch. Long term we don't want to
> carry this patch since it would prevent the vcpu_info mapping code
> from being tested unless a shim with > 32 vCPUs is created, which
> doesn't seem very common.

Just to fill this out a bit:

Without this patch, people need to reboot their L0 hypervisor in order
to use Comet.

With this patch, people only need to compile and update their L0 tools
to use Comet; they can avoid rebooting their L0 hypervisor.

Roger would like to avoid checking this in to staging, because he's
afraid it might make the >32vcpu path bitrot.

The risk of checking it into the Comet branches but not staging is that
if people update their shim to "Rudolph" (4.11) without rebooting their
host, things may unexpectedly not work.  I think that's something we can
live with.

 -George

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