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From:   David Laight <David.Laight@ACULAB.COM>
To:     'Joerg Roedel' <joro@8bytes.org>
CC:     "x86@kernel.org" <x86@kernel.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
        "hpa@zytor.com" <hpa@zytor.com>, Joerg Roedel <jroedel@suse.de>,
        Kees Cook <keescook@chromium.org>,
        Andy Lutomirski <luto@kernel.org>,
        Uros Bizjak <ubizjak@gmail.com>,
        Arvind Sankar <nivedita@alum.mit.edu>,
        Ard Biesheuvel <ardb@kernel.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        Fabio Aiuto <fabioaiuto83@gmail.com>,
        "stable@vger.kernel.org" <stable@vger.kernel.org>
Subject: RE: [PATCH] x86/efi: Restore Firmware IDT in before
 ExitBootServices()
Thread-Topic: [PATCH] x86/efi: Restore Firmware IDT in before
 ExitBootServices()
Thread-Index: AQHXlZXa+jtHdymQB0W1fhKjcUB7Wqt8EPPg///0gwCAABNdkA==
Date:   Fri, 20 Aug 2021 09:02:46 +0000
Message-ID: <f68a175362984e4abbb0a1da2004c936@AcuMS.aculab.com>
References: <20210820073429.19457-1-joro@8bytes.org>
 <e43eb0d137164270bf16258e6d11879e@AcuMS.aculab.com>
 <YR9tSuLyX8QHV5Pv@8bytes.org>
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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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