On 19.04.22 13:57, Peter Zijlstra wrote:
On Tue, Apr 19, 2022 at 11:42:12AM +0000, Andrew Cooper wrote:On 18/04/2022 17:50, Josh Poimboeuf wrote:The startup_xen() kernel entry point is referenced by the ".note.Xen" section, but is presumably not indirect-branched to.It's the real entrypoint of the VM. It's "got to" by setting %rip during vcpu setup. We could in principle support starting a PV VM with CET active, but that sounds like an enormous quantity of effort for very little gain. CET for Xen PV requires paravirt anyway (because the kernel runs in CPL!=0) so decisions like this can wait until someone feels like doing the work.Add ANNOTATE_ENDBR to silence future objtool warnings. Cc: Boris Ostrovsky <[email protected]> Cc: Juergen Gross <[email protected]> Cc: Stefano Stabellini <[email protected]> Cc: [email protected] Signed-off-by: Josh Poimboeuf <[email protected]>FWIW, Reviewed-by: Andrew Cooper <[email protected]>, preferably with the commit message tweaked to remove the uncertainty.Something like so then? --- Subject: x86/xen: Add ANNOTATE_ENDBR to startup_xen() From: Josh Poimboeuf <[email protected]> Date: Mon, 18 Apr 2022 09:50:25 -0700 From: Josh Poimboeuf <[email protected]> The startup_xen() kernel entry point is referenced by the ".note.Xen" section, and is the real entry point of the VM. It *will* be indirectly branched to, *however* currently Xen doesn't support PV VM with CET active.
Hmm, Xen will always use IRET to activate the guest. Juergen
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