linux-kernel - RE: [PATCH V2 1/2] x86/efi: Unmap EFI boot services code/data regions from efi

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Message-ID: <FFF73D592F13FD46B8700F0A279B802F485E5588@ORSMSX114.amr.corp.intel.com>
Date:   Mon, 29 Oct 2018 18:32:36 +0000
From:   "Prakhya, Sai Praneeth" <sai.praneeth.prakhya@...el.com>
To:     Thomas Gleixner <tglx@...utronix.de>
CC:     "linux-efi@...r.kernel.org" <linux-efi@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "x86@...nel.org" <x86@...nel.org>, Borislav Petkov <bp@...en8.de>,
        "Ingo Molnar" <mingo@...nel.org>,
        Andy Lutomirski <luto@...nel.org>,
        "Hansen, Dave" <dave.hansen@...el.com>,
        Bhupesh Sharma <bhsharma@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Ard Biesheuvel <ard.biesheuvel@...aro.org>
Subject: RE: [PATCH V2 1/2] x86/efi: Unmap EFI boot services code/data
 regions from efi_pgd

> > In general it's good to do on list because others can learn from the
> > answers as well.
> 
> So you somehow managed to keep everyone and the lists in CC nevertheless.
> Did not pay attention to the CC list until I got my reply on the list :)

Sorry! my bad.. yes, the conversation did happen on the list and it's by accident.
> 
> > > > > > +	retval = __change_page_attr_set_clr(&cpa, 0);

[........]

> > > So some questions I have are,
> > > 1. What did Peter Z mean here? "How is that not a TLB invalidation bug ?"
> >
> > __flush_tlb_all() flushes only the mapping on the current CPU. So in a
> > SMP environment it's not sufficient.

Thanks for the explanation. The issue makes sense to me now.

[.........]

> > I'll have a second look at the whole thing and reply on list.
> 
> So actually for the problem at hand __flush_tlb_all() works, because that is
> called way before the secondary CPUs are up.
> 
> Ditto for kernel_map_pages_in_pgd().

Yes, you are right. Both the functions are *always* called before SMP initialization
and as you rightly pointed out they should be marked with __init.

> But both functions want to be marked
> __init and aside of that they both should contain a warning when they are called
> after the secondary CPUs have been brought up.

Makes sense too.. I will include these changes in V3.

Regards,
Sai