Re: [PATCH V2 0/6] Enable SMM page level protection.

[Laszlo Ersek <lersek@redhat.com>]

On 11/10/16 15:53, Paolo Bonzini wrote:
> 
> 
> On 10/11/2016 15:48, Yao, Jiewen wrote:
>> I cannot reproduce it before, because all my real hardware supports XD.
>> My Windows QEMU also supports XD (to my surprise.)
> 
> QEMU can be configured to support XD or not.  Possibly Laszlo was using
> some different default, or testing both cases.

When QEMU emulates an Ia32 (32-bit) target, the SMM state save area has
no room for capturing the fact whether NX is set or clear. This is an
issue that dates back to the inception of OVMF's SMM support. The
explanation was given by Paolo, actually :)

  https://www.mail-archive.com/edk2-devel@lists.01.org/msg00970.html

We adjusted the OvmfPkg/README file accordingly:

> * QEMU binary and options specific to 32-bit guests:
>
>   $ qemu-system-i386 -cpu coreduo,-nx \
>
>   or
>
>   $ qemu-system-x86_64 -cpu <MODEL>,-lm,-nx \
>

Note the "-nx" bit.

And, in my recent KVM / QEMU usage instructions for Jiewen:

  https://www.mail-archive.com/edk2-devel@lists.01.org/msg19446.html

I provided the following settings:

> # Settings for Ia32 only:
> [...]
> QEMU_COMMAND="qemu-system-i386 -cpu coreduo,-nx"
>
> # Settings for Ia32X64 only:
> [...]
> QEMU_COMMAND=qemu-system-x86_64

I guess the "-nx" bit can be left off with TCG, but AFAIR it is required
for KVM.

Thanks!
Laszlo