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. :/ Thanks Laszlo
