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

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Message-ID: <20170127221311.GH31613@codeblueprint.co.uk>
Date:   Fri, 27 Jan 2017 22:13:11 +0000
From:   Matt Fleming <matt@...eblueprint.co.uk>
To:     Ard Biesheuvel <ard.biesheuvel@...aro.org>
Cc:     Dave Young <dyoung@...hat.com>,
        Nicolai Stange <nicstange@...il.com>,
        "linux-efi@...r.kernel.org" <linux-efi@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "x86@...nel.org" <x86@...nel.org>, Ingo Molnar <mingo@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        "hpa@...or.com" <hpa@...or.com>,
        Dan Williams <dan.j.williams@...el.com>,
        Mika Penttilä <mika.penttila@...tfour.com>,
        Bhupesh Sharma <bhsharma@...hat.com>
Subject: Re: [PATCH 1/4] efi/x86: make efi_memmap_reserve only insert into
 boot mem areas

On Fri, 27 Jan, at 05:04:50PM, Ard Biesheuvel wrote:
> On 27 January 2017 at 14:48, Matt Fleming <matt@...eblueprint.co.uk> wrote:
> > 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.
> 
> Hmm, I just queued this. Should we drop it again?

Does dropping it break the entire series?

Having had some time to re-read Dave's commit log, it sounds like it
just papers over a bug, which is that efi_memmap_insert() cannot deal
with reserved entries, which all look like they describe the same
region.

So I guess my question is: Shouldn't you fix that instead of requiring
the caller of efi_memmap_insert() to understand what type of entries
it's mapping?