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. 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). 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
