No, not really. Omitting it on the grounds of "we don't expect to take a double fault" don't beat uniformally altering all the entrypoints in a consistent manor.
The only thing which can go wrong is that we forget to do it when it is needed. ~Andrew ________________________________________ From: Jan Beulich [jbeul...@suse.com] Sent: 17 January 2018 08:47 To: Andrew Cooper Cc: Xen-devel Subject: Re: [Xen-devel] [PATCH v8 12/17] x86/entry: Organise the use of MSR_SPEC_CTRL at each entry/exit point >>> On 16.01.18 at 22:24, <andrew.coop...@citrix.com> wrote: > On 15/01/18 12:09, Jan Beulich wrote: >>>>> On 12.01.18 at 19:01, <andrew.coop...@citrix.com> wrote: >>> @@ -586,6 +611,10 @@ ENTRY(double_fault) >>> movl $TRAP_double_fault,4(%rsp) >>> /* Set AC to reduce chance of further SMAP faults */ >>> SAVE_ALL STAC >>> + >>> + SPEC_CTRL_ENTRY_FROM_INTR /* Req: %rsp=regs Clob: acd */ >>> + /* WARNING! `ret`, `call *`, `jmp *` not safe before this point. */ >> Is it actually useful to do _anything_ in the double fault handler? > > Typically no, but then again we hope never to execute this code. > > OTOH, we would need to do this if we ever get around to doing espfix64. Could I get you to omit the change to the handler until then, to keep it as straightforward as possible? Jan _______________________________________________ Xen-devel mailing list Xen-devel@lists.xenproject.org https://lists.xenproject.org/mailman/listinfo/xen-devel
