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 10:33:13 +0900
From:   AKASHI Takahiro <takahiro.akashi@...aro.org>
To:     Ard Biesheuvel <ard.biesheuvel@...aro.org>,
        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 09:42:28AM +0900, AKASHI Takahiro wrote:
> 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.

Oops, it does. Comments at efi_memmap_init_late() say:
---8<---
 * The reason there are two EFI memmap initialisation
 * (efi_memmap_init_early() and this late version) is because the
 * early EFI memmap should be explicitly unmapped once EFI
 * initialisation is complete as the fixmap space used to map the EFI
 * memmap (via early_memremap()) is a scarce resource.
--->8---

> Is it okay to take them out?

Never mind.
> 
> -Takahiro AKASHI