linux-kernel - RE: [PATCH v12 10/18] x86/fsgsbase/64: Enable FSGSBASE instructions in helper functions

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Date:   Tue, 19 May 2020 16:48:05 +0200
From:   Thomas Gleixner <tglx@...utronix.de>
To:     David Laight <David.Laight@...LAB.COM>,
        'Sasha Levin' <sashal@...nel.org>
Cc:     "linux-kernel\@vger.kernel.org" <linux-kernel@...r.kernel.org>,
        "bp\@alien8.de" <bp@...en8.de>,
        "luto\@kernel.org" <luto@...nel.org>,
        "hpa\@zytor.com" <hpa@...or.com>,
        "dave.hansen\@intel.com" <dave.hansen@...el.com>,
        "tony.luck\@intel.com" <tony.luck@...el.com>,
        "ak\@linux.intel.com" <ak@...ux.intel.com>,
        "ravi.v.shankar\@intel.com" <ravi.v.shankar@...el.com>,
        "chang.seok.bae\@intel.com" <chang.seok.bae@...el.com>,
        Andrew Cooper <andrew.cooper3@...rix.com>,
        "x86\@kernel.org" <x86@...nel.org>
Subject: RE: [PATCH v12 10/18] x86/fsgsbase/64: Enable FSGSBASE instructions in helper functions

David Laight <David.Laight@...LAB.COM> writes:
> From: Sasha Levin
>> >> +		native_swapgs();
>> >> +		gsbase = rdgsbase();
>> >> +		native_swapgs();
>
> Does local_irq_save() even do anything useful here.
> You need to actually execute CLI, not just set a
> flag that indicates interrupts shouldn't happen.
> (Which is what I think local_irq_save() might do.)

  local_irq_save()
    raw_local_irq_save()
      arch_local_irq_save()
        arch_local_irq_disable()
          native_irq_disable()
            asm("CLI")

> You also (probably) need to disable NMIs.

The NMI entry can deal with that obviously.

Thanks,

        tglx