linux-kernel - Re: [PATCH v5 05/10] x86, efi: Add efi_fake_mem support for EFI_MEMORY

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Message-ID: <CAPcyv4jv8OacA-P+DFj_d9gq3P-7b9xcr4=m3kx7nTvyko6i2g@mail.gmail.com>
Date:   Fri, 13 Sep 2019 08:02:26 -0700
From:   Dan Williams <dan.j.williams@...el.com>
To:     Ard Biesheuvel <ard.biesheuvel@...aro.org>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        "Rafael J. Wysocki" <rafael.j.wysocki@...el.com>,
        "the arch/x86 maintainers" <x86@...nel.org>,
        Borislav Petkov <bp@...en8.de>, Ingo Molnar <mingo@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Vishal L Verma <vishal.l.verma@...el.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-efi <linux-efi@...r.kernel.org>
Subject: Re: [PATCH v5 05/10] x86, efi: Add efi_fake_mem support for EFI_MEMORY_SP

On Fri, Sep 13, 2019 at 6:02 AM Ard Biesheuvel
<ard.biesheuvel@...aro.org> wrote:
>
> On Fri, 30 Aug 2019 at 03:07, Dan Williams <dan.j.williams@...el.com> wrote:
> >
> > Given that EFI_MEMORY_SP is platform BIOS policy descision for marking
>
> decision

Fixed.

>
> > memory ranges as "reserved for a specific purpose" there will inevitably
> > be scenarios where the BIOS omits the attribute in situations where it
> > is desired. Unlike other attributes if the OS wants to reserve this
> > memory from the kernel the reservation needs to happen early in init. So
> > early, in fact, that it needs to happen before e820__memblock_setup()
> > which is a pre-requisite for efi_fake_memmap() that wants to allocate
> > memory for the updated table.
> >
> > Introduce an x86 specific efi_fake_memmap_early() that can search for
> > attempts to set EFI_MEMORY_SP via efi_fake_mem and update the e820 table
> > accordingly.
> >
>
> Is this early enough? The EFI stub runs before this, and allocates
> memory as well.

Unless I'm missing something the stub only allocates where the kernel
will land. That should be handled by the new mem_avoid_memmap()
extensions to consider "efi_fake_mem" in its exclusions.