linux-kernel - x86: CR4 update when IRQs are enabled

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Message-Id: <E7DBFC7E-3904-483A-89E1-56EC17F14EF1@gmail.com>
Date:   Wed, 8 Nov 2017 13:52:17 -0800
From:   Nadav Amit <nadav.amit@...il.com>
To:     LKML <linux-kernel@...r.kernel.org>,
        Andy Lutomirski <luto@...nel.org>
Subject: x86: CR4 update when IRQs are enabled

I am puzzled by the comment in tlb_state.cr4 , which says:

        /*
         * Access to this CR4 shadow and to H/W CR4 is protected by
         * disabling interrupts when modifying either one.
         */

This does not seem to be true and adding a warning to CR4 writes when
!irqs_disabled() immediately fires in identify_cpu() and
__mcheck_cpu_init_generic(). While these two are called during boot, I think
there other CR4 changes with enabled IRQs, for example, PR_SET_TSC.

So my question(s): Is the comment correct? Is the current behavior correct?

Thanks,
Nadav