linux-kernel - Re: [PATCH V4 3/3] x86/efi: Introduce EFI_PAGE_FAULT

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Date:   Fri, 7 Sep 2018 13:22:07 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Sai Praneeth Prakhya <sai.praneeth.prakhya@...el.com>
Cc:     linux-efi@...r.kernel.org, linux-kernel@...r.kernel.org,
        x86@...nel.org, ricardo.neri@...el.com, matt@...eblueprint.co.uk,
        Al Stone <astone@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Ingo Molnar <mingo@...nel.org>,
        Andy Lutomirski <luto@...nel.org>,
        Bhupesh Sharma <bhsharma@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ard Biesheuvel <ard.biesheuvel@...aro.org>
Subject: Re: [PATCH V4 3/3] x86/efi: Introduce EFI_PAGE_FAULT_HANDLER

On Thu, Sep 06, 2018 at 04:27:48PM -0700, Sai Praneeth Prakhya wrote:
> From: Sai Praneeth <sai.praneeth.prakhya@...el.com>
> 
> There may exist some buggy UEFI firmware implementations that might
> access efi regions other than EFI_RUNTIME_SERVICES_<CODE/DATA> even
> after the kernel has assumed control of the platform. This violates UEFI
> specification.
> 
> If selected, this debug option will print a warning message if the UEFI
> firmware tries to access any memory region which it shouldn't. Along
> with the warning, the efi page fault handler will also try to recover
> from the page fault triggered by the firmware so that the machine
> doesn't hang.

Why make this optional?