linux-kernel - RE: [PATCH] x86/efi: Restore Firmware IDT in before ExitBootServices()

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Date:   Fri, 20 Aug 2021 09:02:46 +0000
From:   David Laight <David.Laight@...LAB.COM>
To:     'Joerg Roedel' <joro@...tes.org>
CC:     "x86@...nel.org" <x86@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        "hpa@...or.com" <hpa@...or.com>, Joerg Roedel <jroedel@...e.de>,
        Kees Cook <keescook@...omium.org>,
        Andy Lutomirski <luto@...nel.org>,
        Uros Bizjak <ubizjak@...il.com>,
        Arvind Sankar <nivedita@...m.mit.edu>,
        Ard Biesheuvel <ardb@...nel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Fabio Aiuto <fabioaiuto83@...il.com>,
        "stable@...r.kernel.org" <stable@...r.kernel.org>
Subject: RE: [PATCH] x86/efi: Restore Firmware IDT in before
 ExitBootServices()

From: 'Joerg Roedel'
> Sent: 20 August 2021 09:52
> 
> On Fri, Aug 20, 2021 at 08:43:47AM +0000, David Laight wrote:
> > Hmmm...
> > If Linux needs its own IDT then temporarily substituting the old IDT
> > prior to a UEFI call will cause 'grief' if a 'Linux' interrupt
> > happens during the UEFI call.
> 
> This is neede only during very early boot before Linux called
> ExitBootServices(). Nothing that causes IRQs is set up by Linux yet. Of
> course the Firmware could have set something up, but Linux runs with
> IRQs disabled when on its own IDT at that stage.

So allocate and initialise the Linux IDT - so entries can be added.
But don't execute 'lidt' until later on.

	David

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