Il 24/07/2013 10:48, Arthur Chunqi Li ha scritto:
> So as what Gleb said, what about the following codes:
>
> static int vmx_run2()
> {
> u32 eax;
> bool ret;
>
> asm volatile(
> "mov %%rsp, %%rsi\n\t"
> "mov %2, %%edi\n\t"
> "call vmcs_write\n\t"
> "vmlaunch\n\t"
> "setbe %0\n\t"
> "jne 4f\n\t"
setbe doesn't set the flags, so you need jbe here (and then you can have
a "mov $1, %0" at label 4 instead of using setbe).
>
> "vmx_return:\n\t"
> SAVE_GPR_C
> "call exit_handler\n\t"
> "cmp %3, %%eax\n\t"
> "je 2f\n\t"
> "cmp %4, %%eax\n\t"
> "je 1f\n\t"
> "jmp 3f\n\t"
>
> /* VMX_TEST_RESUME */
> "1:\n\t"
> LOAD_GPR_C
> "vmresume\n\t"
You need a SAVE_GPR_C here. Then it is better to put the jbe at the
vmx_return label:
... do vmlaunch or vmreturn as Jan said ...
vmx_return:
SAVE_GPR_C
jbe 4f
call exit_handler
etc.
Here is the relevant code from KVM that Jan was referring to:
"jne 1f \n\t"
__ex(ASM_VMX_VMLAUNCH) "\n\t"
"jmp 2f \n\t"
"1: " __ex(ASM_VMX_VMRESUME) "\n\t"
"2: "
I'd prefer to have a "jbe vmx_return; ud2" after the vmlaunch/vmresume,
in order to test that the hypervisor respects HOST_RIP.
Paolo
> "setbe %0\n\t"
> "jne 4f\n\t"
> /* VMX_TEST_VMEXIT */
> "2:\n\t"
> "mov $0, %1\n\t"
> "jmp 5f\n\t"
> /* undefined ret from exit_handler */
> "3:\n\t"
> "mov $2, %1\n\t"
> "jmp 5f\n\t"
> /* vmlaunch/vmresume failed, exit */
> "4:\n\t"
> "mov $1, %1\n\t"
> "5:\n\t"
> : "=r"(ret), "=r"(eax)
> : "i"(HOST_RSP), "i"(VMX_TEST_VMEXIT),
> "i"(VMX_TEST_RESUME)
> : "rax", "rbx", "rdi", "rsi",
> "r8", "r9", "r10", "r11", "r12", "r13", "r14", "r15",
> "memory", "cc"
> );
> switch (eax) {
> case 0:
> return 0;
> case 1:
> printf("%s : vmenter failed.\n", __func__);
> break;
> default:
> printf("%s : unhandled ret from exit_handler.\n", __func__);
> break;
> }
> return 1;
> }
>
> On Wed, Jul 24, 2013 at 2:48 PM, Paolo Bonzini <[email protected]> wrote:
>> Il 24/07/2013 08:46, Arthur Chunqi Li ha scritto:
>>> On Wed, Jul 24, 2013 at 2:40 PM, Paolo Bonzini <[email protected]> wrote:
>>>> Il 24/07/2013 08:11, Arthur Chunqi Li ha scritto:
>>>>>
>>>>> static int vmx_run()
>>>>> {
>>>>> u32 eax;
>>>>> bool ret;
>>>>>
>>>>> vmcs_write(HOST_RSP, get_rsp());
>>>>> ret = vmlaunch();
>>>>
>>>> The compiler can still change rsp between here...
>>>>
>>>>> while (!ret) {
>>>>> asm volatile(
>>>>> "vmx_return:\n\t"
>>>>
>>>> ... and here.
>>>>
>>>> If you want to write it in C, the only thing that can be after
>>>> vmlaunch/vmresume is "exit()". Else it has to be asm.
>>> Actually, you mean we need to write all the codes in asm to avoid
>>> changing to rsp, right?
>>
>> Not necessarily all the code. It is also ok to use setjmp/longjmp with
>> a small asm trampoline, because this method won't care about the exact
>> rsp values that are used. But if you want to do as Gleb said, and put
>> vmx_return just after vmlaunch, it has to be all asm as in KVM's
>> arch/x86/kvm/vmx.c.
>>
>> Paolo
>
>
>
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