[Xen-devel] Re: problem in using MSR in the hypervisor

[Long Wang <longwang.longwang@xxxxxxxxx>]

I added code in the hypervisor to manipulate MSR. Here is my code in
emulate_privileged_op() in the Xen hypervisor:

....
       // for WRMSR
       case MSR_P4_IQ_PERFCTR0:
       case MSR_P4_IQ_CCCR0:
       case MSR_P4_CRU_ESCR0:
       case MSR_P4_IQ_PERFCTR2:
       case MSR_P4_IQ_CCCR2:
       case MSR_P4_CRU_ESCR1:
           wrmsr_safe(regs->ecx, eax, edx);
           break;
......
       // for RDMSR
       case MSR_P4_IQ_PERFCTR0:
       case MSR_P4_IQ_CCCR0:
       case MSR_P4_CRU_ESCR0:
       case MSR_P4_IQ_PERFCTR2:
       case MSR_P4_IQ_CCCR2:
       case MSR_P4_CRU_ESCR1:
               printk("the_cs = 0x%x\n", the_cs);
               __asm__ volatile(
                         "mov %%cs, %0\n"
                         :"=r"(the_cs)
                         :
               );
               printk("the_cs = 0x%x\n", the_cs);
               rdmsr_safe(regs->ecx, regs->eax, regs->edx);
           break;


The wrmsr_safe() and rdmsr_safe() trigger a general protection fault,
and the value read from the msr is 0. But I printed out the cs
descriptor, and found the CPL is 0. Why there is a general protection
fault here? How can I fix this?


thanks,
long

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