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From: Ard Biesheuvel <ard.biesheuvel@linaro.org>
To: Ingo Molnar <mingo@kernel.org>
Cc: Matt Fleming <matt@codeblueprint.co.uk>,
	"H . Peter Anvin" <hpa@zytor.com>,
	Thomas Gleixner <tglx@linutronix.de>,
	"linux-efi@vger.kernel.org" <linux-efi@vger.kernel.org>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	Linus Torvalds <torvalds@linux-foundation.org>,
	Andy Lutomirski <luto@kernel.org>,
	Peter Zijlstra <a.p.zijlstra@chello.nl>
Subject: Re: [PATCH 07/14] efi: runtime-wrappers: Run UEFI Runtime Services with interrupts enabled
Date: Wed, 3 Feb 2016 12:33:10 +0100	[thread overview]
Message-ID: <CAKv+Gu8KZW4m1O5KheBpteOr6tCgNT-FnVkXK-g05=qrzT5xiA@mail.gmail.com> (raw)
In-Reply-To: <20160203105851.GA22159@gmail.com>

On 3 February 2016 at 11:58, Ingo Molnar <mingo@kernel.org> wrote:
>
> * Ard Biesheuvel <ard.biesheuvel@linaro.org> wrote:
>
>> > More fundamentally, this makes me nervous:
>> >
>> >  > The UEFI spec allows Runtime Services to be invoked with interrupts
>> >  > enabled. [...]
>> >
>> > So what really matters is not what the spec says, but how Windows executes
>> > UEFI firmware code in practice.
>> >
>> > If major versions of Windows calls UEFI firmware with interrupts disabled,
>> > then frankly I don't think we should interrupt them under Linux either,
>> > regardless of what the spec says ...
>> >
>> > Random firmware code getting interrupted by the OS changes timings and might
>> > have other side effects the firmware code might not expect - so the question
>> > is, does Windows already de facto allow the IRQ preemption of firmware calls?
>> >
>>
>> Good question. I will try to find out.
>
> Note that if there's a reasonable (but not 100%) case in favor of keeping irqs
> enabled, we can try your patch, with the possibility that we might have to revert
> it, should it cause problems.
>

I think this might have been the reason Matt wanted this in -next
early, but I will let him confirm whether that was the case.

> In practice we probably already interrupt EFI services with NMI interrupts, which
> can be pretty heavy as well if they for example generate printks.
>
> So I'm not against this change in a strong fashion - I'm just a bit cautious and
> it would be nice to know how Windows behaves here.
>

I am not sure how yet, but I am going to try and figure out what
Windows does. I suppose hacking OVMF to record some IRQ mask
information when RT services are being invoked should be sufficient,
but I am going to need some help from someone that understands OVMF
and x86 (Matt?)

  reply	other threads:[~2016-02-03 11:33 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 [this message]
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
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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