linux-kernel - Re: [PATCH v2 3/4] efi/arm: map UEFI memory map earlier on boot

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Date:   Fri, 6 Jul 2018 09:42:28 +0900
From:   AKASHI Takahiro <takahiro.akashi@...aro.org>
To:     Ard Biesheuvel <ard.biesheuvel@...aro.org>
Cc:     Will Deacon <will.deacon@....com>,
        James Morse <james.morse@....com>,
        Catalin Marinas <catalin.marinas@....com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        "Baicar, Tyler" <tbaicar@...eaurora.org>,
        Bhupesh Sharma <bhsharma@...hat.com>,
        Dave Young <dyoung@...hat.com>,
        Mark Rutland <mark.rutland@....com>,
        Al Stone <al.stone@...aro.org>,
        Graeme Gregory <graeme.gregory@...aro.org>,
        Hanjun Guo <hanjun.guo@...aro.org>,
        Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
        Sudeep Holla <sudeep.holla@....com>,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Kexec Mailing List <kexec@...ts.infradead.org>
Subject: Re: [PATCH v2 3/4] efi/arm: map UEFI memory map earlier on boot

On Fri, Jul 06, 2018 at 12:31:49AM +0200, Ard Biesheuvel wrote:
> On 5 July 2018 at 18:48, Will Deacon <will.deacon@....com> wrote:
> > On Thu, Jul 05, 2018 at 12:02:15PM +0100, James Morse wrote:
> >> On 05/07/18 10:43, AKASHI Takahiro wrote:
> >> > On Wed, Jul 04, 2018 at 08:49:32PM +0200, Ard Biesheuvel wrote:
> >> >> On 4 July 2018 at 19:06, Will Deacon <will.deacon@....com> wrote:
> >> >>> On Tue, Jun 19, 2018 at 03:44:23PM +0900, AKASHI Takahiro wrote:
> >> >>>> Since arm_enter_runtime_services() was modified to always create a virtual
> >> >>>> mapping of UEFI memory map in the previous patch, it is now renamed to
> >> >>>> efi_enter_virtual_mode() and called earlier before acpi_load_tables()
> >> >>>> in acpi_early_init().
> >> >>>>
> >> >>>> This will allow us to use UEFI memory map in acpi_os_ioremap() to create
> >> >>>> mappings of ACPI tables using memory attributes described in UEFI memory
> >> >>>> map.
> >>
> >> >>> Hmm, this is ugly as hell. Is there nothing else we can piggy-back off?
> >> >>> It's also fairly jarring that, on x86, efi_enter_virtual_mode() is called
> >> >>> a few lines later, *after* acpi_early_init() has been called.
> >>
> >> >> Currently, there is a gap where we have already torn down the early
> >> >> mapping and haven't created the definitive mapping of the UEFI memory
> >> >> map. There are other reasons why this is an issue, and I recently
> >> >> proposed [0] myself to address one of them
> >>
> >> >> Akashi-san, could you please confirm whether the patch below would be
> >> >> sufficient for you? Apologies for going back and forth on this, but I
> >> >> agree with Will that we should try to avoid warts like the one above
> >> >> in generic code.
> >> >>
> >> >> [0] https://marc.info/?l=linux-efi&m=152930773507524&w=2
> >> >
> >> > I think that this patch will also work.
> >> > Please drop my patch#2 and #3 if you want to pick up my patchset, Will.
> >>
> >> Patch 2 is what changes arm_enable_runtime_services() to map the efi memory map
> >> before bailing out due to efi=noruntime.
> >>
> >> Without it, 'efi=noruntime' means no-acpi-tables.
> >
> > So it sounds like we want patch 2. Akashi, given that this series is only
> > four patches, please can you send out a v3 with the stuff that should be
> > reviewed and merged? Otherwise, there's a real risk we end up with breakage
> > that goes unnoticed initially.
> >
> 
> Yes, we want patches #1, #2 and #4, and this one can be replaced with
> my patch above. Everything can be taken via the arm64 tree as far as I
> am concerned.

I almost believed that my patch#2 was just a preparatory one for patch#3
where arm_enable_runtime_services() is moved aggressively forward.
But acpi_os_ioremap() is not a __init function and I can now agree to
keeping patch#2.

Meanwhile, the consequent code with Ard's patch would look like:
---8<---
static int __init arm_enable_runtime_services(void)
{
        ...
        efi_memmap_unmap();

        mapsize = efi.memmap.desc_size * efi.memmap.nr_map;

        if (efi_memmap_init_late(efi.memmap.phys_map, mapsize)) {
                pr_err("Failed to remap EFI memory map\n");
                return 0;
        }
        ...
}
--->8---
It seems to me that it makes no sense.
Is it okay to take them out?

-Takahiro AKASHI