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). > 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. Thanks, Haozhong > In order to verify if my laptop was indeed capable of LCME, I read the > IA32_MCG_CAP MSR as well: > > # insmod ./rdmsr.ko msr=0x00000179 > MSR 0x179 on CPU 0: 0xc09 > > "MCG_LMCE_P" is bit 27 (value 0x8000000). So, apparently, I was wrong; > my laptop does not support LMCE, and it's not surprising the BIOS > doesn't set the LCME bit in the feature control MSR :) > > Anyway I think you should be able to use the kernel module for > experimenting with MSRs on other hosts. > > Thanks > Laszlo >
