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 22:15:26 +0000
From:   Ard Biesheuvel <ard.biesheuvel@...aro.org>
To:     Matt Fleming <matt@...eblueprint.co.uk>
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 27 January 2017 at 22:13, Matt Fleming <matt@...eblueprint.co.uk> wrote:
> 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.
>

No, it cannot deal with bogus entries, and Peter already fixed that.
Dave confirmed that Peter's patch (the one we moved from next to
urgen) made the problem go away.

> 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?

Indeed. So I don't think the patch is actually needed anymore