linux-kernel - RE: [tip:efi/core] x86/efi: Unmap EFI boot services code/data regions from efi

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Message-ID: <FFF73D592F13FD46B8700F0A279B802F486045CA@ORSMSX114.amr.corp.intel.com>
Date:   Mon, 17 Dec 2018 18:42:23 +0000
From:   "Prakhya, Sai Praneeth" <sai.praneeth.prakhya@...el.com>
To:     Ard Biesheuvel <ard.biesheuvel@...aro.org>
CC:     Ingo Molnar <mingo@...nel.org>,
        "tglx@...utronix.de" <tglx@...utronix.de>,
        "x86@...nel.org" <x86@...nel.org>, "bp@...en8.de" <bp@...en8.de>,
        "marc.zyngier@....com" <marc.zyngier@....com>,
        "eric.snowberg@...cle.com" <eric.snowberg@...cle.com>,
        "hdegoede@...hat.com" <hdegoede@...hat.com>,
        "Hansen, Dave" <dave.hansen@...el.com>,
        "peterz@...radead.org" <peterz@...radead.org>,
        "hpa@...or.com" <hpa@...or.com>,
        "arend.vanspriel@...adcom.com" <arend.vanspriel@...adcom.com>,
        "julien.thierry@....com" <julien.thierry@....com>,
        "bhsharma@...hat.com" <bhsharma@...hat.com>,
        "jonathanh@...dia.com" <jonathanh@...dia.com>,
        "joe@...ches.com" <joe@...ches.com>,
        "matt@...eblueprint.co.uk" <matt@...eblueprint.co.uk>,
        "torvalds@...ux-foundation.org" <torvalds@...ux-foundation.org>,
        "natechancellor@...il.com" <natechancellor@...il.com>,
        "luto@...nel.org" <luto@...nel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "sedat.dilek@...il.com" <sedat.dilek@...il.com>,
        "zhuyifei1999@...il.com" <zhuyifei1999@...il.com>,
        "linux-tip-commits@...r.kernel.org" 
        <linux-tip-commits@...r.kernel.org>
Subject: RE: [tip:efi/core] x86/efi: Unmap EFI boot services code/data
 regions from efi_pgd

> > Hi Thomas and Ingo,
> >
> > I recently noticed that the below commits [1] and [2] are broken when
> > kernel command line argument "efi=old_map" is passed. Sorry! I missed
> > to test this condition prior to sending these patches to mailing list.
> > I am working on a fix and will send it to mailing list as soon as it's ready.
> >
> 
> Could you elaborate on the problem please?

Sure! My bad..

Little bit of history here:
Boris with this patch set [1] introduced statically mapping EFI Runtime Services at -4G 
and also introduced "efi=old_map" to return to previous EFI functionality which used 
ioremap and __va(pa).

[3] and [4] are links to old_map_region()

The commit 08cfb38f3ef4 ("x86/efi: Unmap EFI boot services code/data regions from efi_pgd"), 
unmaps EFI boot services code/data regions *only* from efi_pgd but efi=old_map maps 
EFI boot services code/data regions into swapper_pgd. Also, efi=old_map  uses either 
ioremap() or __va(md->phys_addr) to map EFI runtime/boot time services and doesn't use kernel_map_pages_in_pgd().

So, we need a different unmapping routine to unmap EFI boot services code/data 
regions from swapper_pgd if they were mapped using efi=old_map.

[1] https://lkml.org/lkml/2013/9/19/235 - Cover letter for EFI runtime services virtual mapping
[2] https://lkml.org/lkml/2013/10/8/777 - Talks about efi=old_map
[3] https://elixir.bootlin.com/linux/v4.20-rc7/source/arch/x86/platform/efi/efi_64.c#L429
[4] https://elixir.bootlin.com/linux/v4.20-rc7/source/arch/x86/platform/efi/efi.c#L584

> 
> > Meanwhile, could you please drop these patches before sending pull request
> to Linus?
> >
> > [1] Commit 08cfb38f3ef4 ("x86/efi: Unmap EFI boot services code/data
> > regions from efi_pgd") [2] Commit 7e0dabd3010d ("x86/mm/pageattr:
> > Introduce helper function to unmap EFI boot services")
> >
> 
> I'd like to understand what the issue is before we drop anything.

Regards,
Sai