Re: [libvirt] [Qemu-devel] Configuring pflash devices for OVMF firmware
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.
Paolo