Re: [Qemu-devel] [PATCH 23/31] ich9: implement SMI_LOCK

[Paolo Bonzini <pbonzini@redhat.com>]

On 11/05/2015 17:36, Laszlo Ersek wrote:
> It's not about feature detection -- the question (from
> <553F4D23.3060305@redhat.com>) is whether I should set APMC_EN myself
> *every time* before writing to APM_CNT, in the
> EFI_SMM_CONTROL2_PROTOCOL.Trigger() method. That protocol is provided by
> a runtime DXE driver and would be exercised by eg. the non-privileged
> half of the runtime variable service driver.

Oh sorry, I couldn't find that message ID.

> It's no problem to set it, I have the code ready, I was just wondering
> if I should keep that hunk. (In fact it might not even matter: if the OS
> interferes and clears APMC_EN before the non-privileged half mentioned
> above manages to raise the SMI, then the call / transition to SMM will
> simply not happen, which is bad for the OS, and probably irrelevant for
> the firmware (... the security thereof).)

The OS can also race against you and clear APMC_EN, so it's even
unnecessary to reset it.

Paolo