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From: Matt Fleming <matt@codeblueprint.co.uk>
To: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Cc: Andy Lutomirski <luto@amacapital.net>,
	"H. Peter Anvin" <hpa@zytor.com>,
	"linux-efi@vger.kernel.org" <linux-efi@vger.kernel.org>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	Thomas Gleixner <tglx@linutronix.de>,
	Sai Praneeth Prakhya <sai.praneeth.prakhya@intel.com>,
	Ingo Molnar <mingo@kernel.org>,
	Linus Torvalds <torvalds@linux-foundation.org>,
	Peter Zijlstra <a.p.zijlstra@chello.nl>
Subject: Re: [PATCH] efi: runtime-wrappers: run UEFI Runtime Services with interrupts enabled
Date: Thu, 11 Feb 2016 16:03:54 +0000	[thread overview]
Message-ID: <20160211160354.GJ4134@codeblueprint.co.uk> (raw)
In-Reply-To: <CAKv+Gu_sPq9wesOpEREyopVddpVW2P7m8YCDHHcBHkLk-kH+ew@mail.gmail.com>

On Tue, 09 Feb, at 05:52:34PM, Ard Biesheuvel wrote:
> On 8 February 2016 at 20:37, Andy Lutomirski <luto@amacapital.net> wrote:
> > On Feb 4, 2016 5:58 AM, "Ard Biesheuvel" <ard.biesheuvel@linaro.org> wrote:
> >>
> >> OK, since Sai has confirmed that Windows leaves interrupts enabled when
> >> calling the EFI variable store related runtime services, we should be able
> >> to do the same for Linux, or at least be slightly more confident that we
> >> won't have to back out this change later.
> >
> > Could this use a mutex instead of a spinlock?
> >
> 
> When I first started working on this code, I proposed using a mutex,
> but at the time, we still had the efi-pstore case to worry about
> http://article.gmane.org/gmane.linux.kernel.efi/4112
> 
> In the mean time, we have modified the efi-pstore code so it simply
> gives up when the EFI varstore is busy, and we also got rid of the NMI
> special case where locks are ignored. In summary, it sounds to me that
> moving to a mutex should be feasible, but I am only really familiar
> with the ARM side of the implementation, which is far less complex
> than the x86 side, so Matt should confirm.

You cannot touch mutexes from interrupt context, not even to perform a
mutex_trylock(), and that's the problem.

Since the efi-pstore code can run from interrupt context we need to
use a locking primitive that works, even though we have all that
non-blocking logic. 

  reply	other threads:[~2016-02-11 16:03 UTC|newest]

Thread overview: 67+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2016-02-01 22:06 [GIT PULL 00/14] EFI changes for v4.6 Matt Fleming
2016-02-01 22:06 ` [PATCH 01/14] efi: Expose non-blocking set_variable() wrapper to efivars Matt Fleming
2016-02-03 11:31   ` [tip:efi/core] " tip-bot for Ard Biesheuvel
2016-02-01 22:06 ` [PATCH 02/14] efi: Remove redundant efi_set_variable_nonblocking prototype Matt Fleming
2016-02-01 22:06   ` Matt Fleming
2016-02-03 11:31   ` [tip:efi/core] efi: Remove redundant efi_set_variable_nonblocking () prototype tip-bot for Ard Biesheuvel
2016-02-01 22:06 ` [PATCH 03/14] efi: runtime-wrappers: Add a nonblocking version of QueryVariableInfo Matt Fleming
2016-02-01 22:06   ` Matt Fleming
2016-02-03 11:31   ` [tip:efi/core] efi/runtime-wrappers: Add a nonblocking version of QueryVariableInfo() tip-bot for Ard Biesheuvel
2016-02-01 22:06 ` [PATCH 04/14] efi: Add nonblocking option to efi_query_variable_store() Matt Fleming
2016-02-03 11:32   ` [tip:efi/core] " tip-bot for Ard Biesheuvel
2016-02-01 22:06 ` [PATCH 05/14] efi: runtime-wrappers: Remove out of date comment regarding in_nmi() Matt Fleming
2016-02-03 11:32   ` [tip:efi/core] efi/runtime-wrappers: " tip-bot for Ard Biesheuvel
2016-02-01 22:07 ` [PATCH 06/14] efi: runtime-wrapper: Get rid of the rtc_lock spinlock Matt Fleming
2016-02-01 22:07   ` Matt Fleming
2016-02-03 11:32   ` [tip:efi/core] efi: Runtime-wrapper: " tip-bot for Ard Biesheuvel
2016-02-01 22:07 ` [PATCH 07/14] efi: runtime-wrappers: Run UEFI Runtime Services with interrupts enabled Matt Fleming
2016-02-03  9:43   ` Ingo Molnar
2016-02-03  9:57     ` Ard Biesheuvel
2016-02-03  9:57       ` Ard Biesheuvel
2016-02-03 10:58       ` Ingo Molnar
2016-02-03 11:33         ` Ard Biesheuvel
2016-02-03 12:01           ` Matt Fleming
2016-02-04 13:58         ` [PATCH] efi: runtime-wrappers: run " Ard Biesheuvel
2016-02-08 15:16           ` Matt Fleming
2016-02-08 19:37           ` Andy Lutomirski
2016-02-09 16:52             ` Ard Biesheuvel
2016-02-09 16:52               ` Ard Biesheuvel
2016-02-11 16:03               ` Matt Fleming [this message]
2016-02-11 16:04             ` Matt Fleming
2016-02-01 22:07 ` [PATCH 08/14] efivars: Use to_efivar_entry Matt Fleming
2016-02-03 11:33   ` [tip:efi/core] " tip-bot for Geliang Tang
2016-02-01 22:07 ` [PATCH 09/14] x86/efi-bgrt: Don't ignore the BGRT if the 'valid' bit is 0 Matt Fleming
2016-02-03 11:33   ` [tip:efi/core] x86/efi/bgrt: " tip-bot for Môshe van der Sterre
2016-02-01 22:07 ` [PATCH 10/14] efi: Make checkpatch complain less about efi.h GUID additions Matt Fleming
2016-02-01 22:07   ` Matt Fleming
2016-02-03 10:33   ` Ingo Molnar
2016-02-03 10:33     ` Ingo Molnar
2016-02-03 10:44     ` Matt Fleming
2016-02-03 10:50       ` Ingo Molnar
2016-02-03 10:50         ` Ingo Molnar
2016-02-03 11:18         ` Matt Fleming
2016-02-03 11:27           ` Ingo Molnar
2016-02-03 11:27             ` Ingo Molnar
2016-02-03 11:09     ` Joe Perches
2016-02-01 22:07 ` [PATCH 11/14] x86/efi: Show actual ending addresses in efi_print_memmap Matt Fleming
2016-02-02  8:49   ` Laszlo Ersek
2016-02-03 11:33   ` [tip:efi/core] " tip-bot for Robert Elliott
2016-02-01 22:07 ` [PATCH 12/14] efi: Add NV memory attribute Matt Fleming
2016-02-02  8:54   ` Laszlo Ersek
2016-02-02  8:54     ` Laszlo Ersek
2016-02-03 11:34   ` [tip:efi/core] " tip-bot for Robert Elliott
2016-02-01 22:07 ` [PATCH 13/14] efi: Add Persistent Memory type name Matt Fleming
2016-02-02  8:56   ` Laszlo Ersek
2016-02-03 11:34   ` [tip:efi/core] " tip-bot for Robert Elliott
2016-02-01 22:07 ` [PATCH 14/14] x86/efi: Print size in binary units in efi_print_memmap Matt Fleming
2016-02-02  9:22   ` Laszlo Ersek
2016-02-03 10:40     ` Ingo Molnar
2016-02-03 11:28       ` Matt Fleming
2016-02-03 12:36         ` Andy Shevchenko
2016-02-03 15:25         ` Elliott, Robert (Persistent Memory)
2016-02-03 15:25           ` Elliott, Robert (Persistent Memory)
2016-02-09 12:20           ` Ingo Molnar
2016-02-09 12:53             ` Laszlo Ersek
2016-02-09 12:53               ` Laszlo Ersek
2016-02-09 13:14               ` Ingo Molnar
2016-02-09 13:14                 ` Ingo Molnar

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