[SeaBIOS] [PATCH v3] fw/msr_feature_control: add support to set MSR_IA32_FEATURE_CONTROL

[Haozhong Zhang]

On 07/06/16 08:42, Laszlo Ersek wrote:
> On 07/06/16 08:28, Haozhong Zhang wrote:
> > Hi Ashok,
> > 
> > On 07/06/16 02:18, Paolo Bonzini wrote:
> >>> I forgot to restore MSR_IA32_FEATURE_CONTROL in the resume path, and
> >>> MSR_IA32_FEATURE_CONTROL is zero after S3 resume.
> >>
> >> This is a bug.  Sorry Laszlo. :)
> >>
> >>> Not restore MSR_IA32_FEATURE_CONTROL during S3 resume does not affect
> >>> at least Linux guest (tested 4.5). Current QEMU may advise the guest
> >>> firmware to set bit 20 (for LMCE), bit 2 (for VMX) and bit 0 (lock
> >>> bit).
> >>> - For LMCE, Linux only checks bit 20 and bit 0 at boot time and then
> >>>   keeps using the result even after resume.
> >>
> >> On real hardware, LMCE would not be enabled after resume.  I'm not
> >> sure what would happen, but it wouldn't be good.
> > 
> > Could you help to check if the LMCE bit in MSR_IA32_FEATURE_CONTROL is
> > set after S3 resume on the real hardware?
> 
> The SDM says that IA32_FEATURE_CONTROL is zeroed on logical processor reset.
> 
>   23.7 ENABLING AND ENTERING VMX OPERATION
> 
>   [...] VMXON is also controlled by the IA32_FEATURE_CONTROL MSR (MSR
>   address 3AH). This MSR is cleared to zero when a logical processor is
>   reset. [...]
> 

Ah, I missed a bit in my question. I meant to check whether the
firmware on the real machine sets the LMCE bit and other necessary
bits in MSR_IA32_FEATURE_CONTROL after S3 resume.