linux-kernel - Re: [PATCH 1/4] efi/x86: make efi_memmap_reserve only insert into boot mem areas

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Date:   Fri, 27 Jan 2017 14:48:13 +0000
From:   Matt Fleming <matt@...eblueprint.co.uk>
To:     Dave Young <dyoung@...hat.com>
Cc:     Nicolai Stange <nicstange@...il.com>,
        Ard Biesheuvel <ard.biesheuvel@...aro.org>,
        linux-efi@...r.kernel.org, linux-kernel@...r.kernel.org,
        x86@...nel.org, Ingo Molnar <mingo@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>, hpa@...or.com,
        Dan Williams <dan.j.williams@...el.com>,
        mika.penttila@...tfour.com, bhsharma@...hat.com
Subject: Re: [PATCH 1/4] efi/x86: make efi_memmap_reserve only insert into
 boot mem areas

On Fri, 13 Jan, at 05:29:52AM, Dave Young wrote:
> 
> It sounds reasonable though I'm still not sure about EFI_LOADER*.
> 
> The main purpose of this patch is to address the invalid mem ranges
> case. As Ard mentioned I will test with Peter's patch first, if it works
> fine I would like to either drop this patch as a future improvement or add
> it at the end of the next post.
> 
> Matt, what's your opinion about the boot_only check and the EFI_LOADERS*
> question?

The main reason that efi_mem_reserve() isn't used for EFI_LOADER
regions today is because we already have a mechanism for reserving it
via memblock_reserve(), which we do during a very early stage of boot
when parsing all the different types of SETUP_* objects.

It's questionable whether it would make sense to switch to
efi_mem_reserve() for EFI_LOADER regions because then you'd
potentially have different APIs for different SETUP_* objects.

As things stand today, I would suggest triggering a WARN_ON() if
someone tries to efi_mem_reserve() an EFI_LOADER region, until/unless
the day comes when a user exists in the kernel.