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From: Markus Armbruster <armbru@redhat.com>
To: Paolo Bonzini <pbonzini@redhat.com>
Cc: Peter Maydell <peter.maydell@linaro.org>,
	Peter Krempa <pkrempa@redhat.com>,
	Qemu-block <qemu-block@nongnu.org>,
	Libvirt <libvir-list@redhat.com>,
	QEMU Developers <qemu-devel@nongnu.org>,
	Laszlo Ersek <lersek@redhat.com>
Subject: Re: [Qemu-devel] Configuring pflash devices for OVMF firmware
Date: Thu, 31 Jan 2019 13:51:50 +0100	[thread overview]
Message-ID: <87y3717zx5.fsf@dusky.pond.sub.org> (raw)
In-Reply-To: <0871cdaf-6a78-1dd7-d18b-ae1337a1a54e@redhat.com> (Paolo Bonzini's message of "Thu, 31 Jan 2019 13:10:33 +0100")

Paolo Bonzini <pbonzini@redhat.com> writes:

> On 31/01/19 10:37, Markus Armbruster wrote:
>>>
>>>> Hmm, why is it okay to treat all pfl->cmd values the same when
>>>> secure=on?
>>> But doesn't matter.  You just don't want MMIO mode to be active outside
>>> SMM: all that non-SMM code want to do with the flash is read and execute
>>> it, as far as they're concerned it's just ROM and the command mode is
>>> nonexistent.
>> Out of curiosity: what effect does secure=on have when the device is
>> read-only (pflash_t member ro non-zero)?
>
> Non-SMM code cannot execute commands.  This means two things:
>
> First, in addition to writes, there are nondestructive commands such as
> read device id.  Those are also inaccessible to non-SMM if secure=on.
> Again, for non-SMM code it looks like your old ROM.  This is not
> important but...
>
> ... CFI commands, even commands that are nondestructive or writes that
> fail because of readonly-ness, consist of multiple writes to the flash
> device.  If non-SMM code could issue a partial command, the SMM flash
> driver would likely end up confused.  Therefore it's probably a good
> idea to make all parallel flash devices have secure=on even if the
> content of the flash cannot be damaged, and that's why I never
> considered anything but -global to configure the property.

Makes sense now, thanks!

  reply	other threads:[~2019-01-31 12:52 UTC|newest]

Thread overview: 45+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-01-25 15:03 [Qemu-devel] Configuring pflash devices for OVMF firmware Markus Armbruster
2019-01-28  7:58 ` Laszlo Ersek
2019-01-28 10:39 ` Peter Maydell
2019-01-28 12:40   ` [Qemu-devel] [libvirt] " Gerd Hoffmann
2019-01-28 13:06     ` Peter Maydell
2019-01-28 14:55       ` Laszlo Ersek
2019-01-28 14:58         ` Peter Maydell
2019-01-28 15:03           ` Laszlo Ersek
2019-01-30  7:36       ` Markus Armbruster
2019-01-30  8:00         ` Gerd Hoffmann
2019-01-30  7:24   ` [Qemu-devel] " Markus Armbruster
2019-01-30 15:24     ` Peter Maydell
2019-01-30 16:44       ` Laszlo Ersek
2019-01-30 17:24         ` Peter Maydell
2019-01-31  8:52           ` Markus Armbruster
2019-01-31 10:01             ` Peter Maydell
2019-01-31 10:24               ` Markus Armbruster
2019-01-31 10:34                 ` Peter Maydell
2019-01-31 12:05                   ` Markus Armbruster
2019-01-30 14:13   ` Markus Armbruster
2019-01-30 14:33     ` Paolo Bonzini
2019-01-30 16:38       ` Laszlo Ersek
2019-01-31  8:33         ` Markus Armbruster
2019-01-31  9:19           ` Paolo Bonzini
2019-01-31  9:37             ` Markus Armbruster
2019-01-31 12:02               ` Laszlo Ersek
2019-01-31 12:10               ` Paolo Bonzini
2019-01-31 12:51                 ` Markus Armbruster [this message]
2019-01-31  8:40       ` Markus Armbruster
2019-01-31  9:19         ` Paolo Bonzini
2019-01-31  9:41           ` Markus Armbruster
2019-01-31 10:12             ` Paolo Bonzini
2019-01-31 12:12               ` Markus Armbruster
2019-01-31 22:57                 ` Paolo Bonzini
2019-01-31 23:28                   ` Alexandro Sanchez Bach
2019-01-31 23:54                     ` Paolo Bonzini
2019-02-01  2:49                       ` Ning, Yu
2019-02-04 10:00                         ` Paolo Bonzini
2019-02-01  8:58                   ` Markus Armbruster
2019-01-31 11:57           ` Laszlo Ersek
2019-02-19  7:19       ` Markus Armbruster
2019-02-22 13:28         ` Markus Armbruster
2019-02-07  9:30 ` Markus Armbruster
2019-02-07 12:31   ` Laszlo Ersek
2019-02-07 13:49     ` Markus Armbruster

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