linux-kernel - Re: 2f47e7e19f ("x86/mm/kaiser: Use PCID feature to make user and .."): WARNING: CPU: 0 PID: 1 at mm/early_ioremap.c:114 __early

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Date:   Mon, 27 Nov 2017 17:22:02 -0800
From:   Dave Hansen <dave.hansen@...ux.intel.com>
To:     "Rafael J. Wysocki" <rafael@...nel.org>
Cc:     Ingo Molnar <mingo@...nel.org>,
        kernel test robot <fengguang.wu@...el.com>, LKP <lkp@...org>,
        kvm@...r.kernel.org,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Thomas Gleixner <tglx@...utronix.de>, wfg@...ux.intel.com,
        "Rafael J. Wysocki" <rjw@...ysocki.net>,
        ACPI Devel Maling List <linux-acpi@...r.kernel.org>,
        "Brown, Len" <len.brown@...el.com>,
        Jesse Barnes <jbarnes@...tuousgeek.org>,
        Bjorn Helgaas <bhelgaas@...gle.com>
Subject: Re: 2f47e7e19f ("x86/mm/kaiser: Use PCID feature to make user and
 .."): WARNING: CPU: 0 PID: 1 at mm/early_ioremap.c:114 __early_ioremap

I think I narrowed this down.

__native_flush_tlb_single() depends on cpu_tlbstate.loaded_mm_asid
matching what is in CR3.  But, while we are still "early" in boot, CR3
has hardware ASID=0, but cpu_tlbstate.loaded_mm_asid=0 which is actually
hardware ASID=1.

So, we have ASID=0 in CR3 and we try to *flush* ASID=1 with INVPCID,
which does nothing for us, effectively missing the TLB flush.

I think we need to steer __native_flush_tlb_single() into the
"!this_cpu_has(X86_FEATURE_INVPCID_SINGLE)" path if we get called before
initialize_tlbstate_and_flush() gives us a "real" ASID in CR3, but I
haven't found a nice way to do it, yet.

We probably also need a debugging warning in there to read CR3 and check
it against cpu_tlbstate.loaded_mm_asid.  I'll look at this in some more
detail tomorrow if nobody beats me to it.