On 07/06/16 11:00, Laszlo Ersek wrote: > On 07/06/16 10:48, Haozhong Zhang wrote: > > On 07/06/16 09:44, Laszlo Ersek wrote: > >> On 07/06/16 08:49, Haozhong Zhang wrote: > >>> 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. > >>> > >> > >> I attached a minimal kernel module (reproducer / tester) to the github > >> issue here: > >> > >> https://github.com/tianocore/edk2/issues/97#issuecomment-230697897 > >> > >> We can use it for both testing the feature in guests, and for querying > >> the MSR on physical machines. > >> > > > > Thanks for the kernel module! In fact, I'm using the rdmsr command > > provided by msr-tools (which is included in some Linux distros). > > Welp, that package is available on RHEL-7 too (from EPEL), I just didn't > have it installed. (I guessed that the command would be called "rdmsr", > and tried to run it, but when that failed, I didn't look for any packages.) > > >> Specifically on my ThinkPad W541, the MSR has value 0x5: > >> > >> [ 2885.877339] MSR 0x3a on CPU 0: 0x5 > >> [ 2908.151693] MSR 0x3a on CPU 1: 0x5 > >> > >> which, according to > >> > >> #define FEATURE_CONTROL_LOCKED (1<<0) > >> #define FEATURE_CONTROL_VMXON_ENABLED_INSIDE_SMX (1<<1) > >> #define FEATURE_CONTROL_VMXON_ENABLED_OUTSIDE_SMX (1<<2) > >> #define FEATURE_CONTROL_LMCE (1<<20) > >> > >> corresponds to > >> > >> (FEATURE_CONTROL_LOCKED | FEATURE_CONTROL_VMXON_ENABLED_OUTSIDE_SMX). > >> > >> FEATURE_CONTROL_LMCE is not set at all. (I didn't do any S3 cycles in my > >> current laptopt boot.) > >> > >> My CPU is i7-4810MQ. It's a pretty modern laptop, so I think it is > >> capable of LMCE, hardware-wise (if LMCE is hw-dependent, to begin with). > >> > > > > LMCE is supported only by server CPUs (Skylake-EX or later) and not > > available on desktop CPUs. > > > > For test in guest, you could follow what I added in "How to verify?" > > https://github.com/tianocore/edk2/issues/97. > > Great, apparently I can't even read. Those steps are in the first > comment. :/ >
I supposed every modification in github issues would trigger mail notifications to others, but apparently it does not. I'll take care in the future. Haozhong
