Re: [PATCH] gfxboot VMX workaround v2

[Anthony Liguori <anthony@codemonkey.ws>]

Guillaume Thouvenin wrote:
> On Tue, 15 Apr 2008 16:06:43 +0300
> Avi Kivity <avi@qumranet.com> wrote:
>
>   
>>> ...
>>> handle_vmentry_failure: invalid guest state
>>> handle_vmentry_failure: start emulation
>>> handle_vmentry_failure: emulation failed
>>>   
>>>       
>> What instruction failed, exactly?
>>
>>     
>
> I added the code do dump the instruction and it seems that it's the
> emulation of 0xe6 (== out imm8, al) that failed. I made modifications
> to emulate it (see below) and now I have another problem in kvm
> userspace with the following message (and the emulation doesn't work):
>
> enterprise:~ $ kvm_run: Operation not permitted
> enterprise:~ $ kvm_run returned -1
>  
>   
>> You need to load rip as well.
>>     
>
> Ooops, yes. So jump far emulation is now like:
>
> +       case 0xea: /* jmp far */ {
> +               struct kvm_segment kvm_seg;
> +               long int eip;
> +               int ret;
> +
> +               kvm_x86_ops->get_segment(ctxt->vcpu, &kvm_seg, VCPU_SREG_CS); 
> +
> +               ret = load_segment_descriptor(ctxt->vcpu, kvm_seg.selector, 9, VCPU_SREG_CS);
> +               if (ret < 0){
> +                       printk(KERN_INFO "%s: Failed to load CS descriptor\n", __FUNCTION__);
> +                       goto cannot_emulate;
> +               }
> +
> +               switch (c->op_bytes) {
> +               case 2:
> +                       eip = insn_fetch(s16, 2, c->eip);
> +                       break;
> +               case 4:
> +                       eip = insn_fetch(s32, 4, c->eip);
> +                       break;
> +               default:
> +                       DPRINTF("jmp far: Invalid op_bytes\n");
> +                       goto cannot_emulate;
> +               }
> +               printk(KERN_INFO "eip == 0x%lx\n", eip);
> +               c->eip = eip;
> +               break;
> +       }
>
> It seems that the jump to cs:eip works and now I have the following error:
>
> [18535.446917] handle_vmentry_failure: invalid guest state
> [18535.449519] handle_vmentry_failure: start emulation
> [18535.457519] eip == 0x6e18
> [18535.467685] handle_vmentry_failure: emulation of 0xe6 failed
>
> For the emulation of 0xe6 I used the following one that I found in
> nitin's tree:
>   

This doesn't seem right.  You should have been able to break out of the 
emulator long before encountering an out instruction.  The next 
instruction you encounter should be a mov instruction.  Are you sure 
you're updating eip correctly?

Regards,

Anthony Liguori

> +       case 0xe6: /* out imm8, al */
> +       case 0xe7: /* out imm8, ax/eax */ {
> +               struct kvm_io_device *pio_dev;
> +               
> +               pio_dev = vcpu_find_pio_dev(ctxt->vcpu, c->src.val);
> +               kvm_iodevice_write(pio_dev, c->src.val,
> +                               (c->d & ByteOp) ? 1 : c->op_bytes,
> +                               &c->regs[VCPU_REGS_RAX]);
> +               }
> +               break;
>
> I will look closer where is the problem and as you suggested, I will
> display the instruction to be emulated and the register state before
> and after, and compare with the expected state.
>
>
> Thanks for your help,
> Regards,
> Guillaume
>
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