[MODERATED] Re: [patch 3/8] [PATCH v1.3.1 3/7] Linux Patch 3

[Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>]

On Thu, Apr 19, 2018 at 11:10:03PM +0200, speck for Borislav Petkov wrote:
> On Thu, Apr 19, 2018 at 04:51:37PM -0400, speck for Konrad Rzeszutek Wilk wrote:
> > That won't work. The reason is that check_bugs first calls
> > identify_boot_cpu() which calls identify_cpu() which calls
> > this_cpu->init. Once identify_boot_cpu() is done _then_ it walks
> > through the spectre_v2_select_mitigation() and ssb_select_mitigation().
> 
> So call md_select_mitigation() before identify_boot_cpu() in
> check_bugs().

That will mean that the init_speculation_control() won't happen
until _after_ md_select_mitigation().

And that throws a wrench in that as we need to rdmsrl(SPEC_CTRL)
(which is right now done from spectre_v2_select_mitigation):

347         if (boot_cpu_has(X86_FEATURE_IBPB) || boot_cpu_has(X86_FEATURE_IBRS))
348                 rdmsrl(MSR_IA32_SPEC_CTRL, x86_spec_ctrl_base);
349 }

And x86_spec_ctrl_base is then ORed in md_select_mitigation().

But
spectre_v2_select_mitigation depends on identify_boot_cpu.
md_select_mitigation depends on spectre_v2_select_mitigation.

If I move the identify_boot_cpu before md_select_mitigation things
get wonky.

Maybe it will be easier to explain when I send out the patches?