On Sun, Jun 9, 2013 at 10:09 PM, Gleb Natapov <gleb@xxxxxxxxxx> wrote:
> On Sun, Jun 09, 2013 at 09:22:27PM +0800, 李春奇 <Arthur Chunqi Li> wrote:
>> On Sun, Jun 9, 2013 at 8:49 PM, Gleb Natapov <gleb@xxxxxxxxxx> wrote:
>> > On Sun, Jun 09, 2013 at 08:44:32PM +0800, 李春奇 <Arthur Chunqi Li> wrote:
>> >> On Sun, Jun 9, 2013 at 7:07 PM, Gleb Natapov <gleb@xxxxxxxxxx> wrote:
>> >> > On Fri, Jun 07, 2013 at 10:31:38AM +0800, Arthur Chunqi Li wrote:
>> >> >> Add a function trap_emulator to run an instruction in emulator.
>> >> >> Set inregs first (%rax, %rsp, %rbp, %rflags have special usage and
>> >> >> cannot set in inregs), put instruction codec in alt_insn and call
>> >> >> func with alt_insn_length. Get results in outregs.
>> >> >>
>> >> > Why %rax, %rsp, %rbp, %rflags cannot be set in inregs?
>> >> >
>> >> > %rax because trapping instruction uses it? Use one that does not use
>> >> > register at all: MOV r/m32, imm32
>> >> I don't know why set %rax before call alt_insn_page can cause error. I
>> >> use "xchg %%rax, 0+%[save]" before "call *%1" and the %rcx is not set
>> >> correctly.
>> > We better find this out :)
>> I found that before calling alt_insn_page, address of "mem" is saved
>> to %rax, why?
> Because instruction that we use to trigger vmexit is mov %eax, (%rax) so
> MMOI address mem is loaded into %rax before jumping into it.
I think this is why changing %rax will cause error. If we use mov
%eax, (%rax) to trigger vmexit, and %rax is changed before calling
alt_insn_page, codes in alt_insn_page will not be executed and return
directly.
I changed the codes which trigger vmexit to "mov %eax, (%r8)" and set
"mem" to %r8 before calling alt_insn_page, it runs OK.
Besides, I also don't know if changed %rflags may cause some
unpredictable actions, so now we just treat it with no error :)
>
>> >
>> >> >
>> >> > %rsp and %rbp because of ret on instruction page? Use the same trick
>> >> > realmode.c test uses: have the code that sets/saves registers in
>> >> > insn_page/alt_insn_page itself and copy the instruction you want to test
>> >> > into the page itself instead of doing call.
>> >> I don't know how instructions between calling insn_page and
>> >> alt_insn_page are executed (function install_page and some other
>> >> instructions before call *%1". If these insns are executed after
>> >> insn_page is called, changes before the trapping instruction may
>> >> affect the executing of these instructions.
>> >>
>> > Not sure what do you mean here.
>> >
>> >> >
>> >> > Not sure what is so special about %rflags.
>> >> >
>> >> >> Signed-off-by: Arthur Chunqi Li <yzt356@xxxxxxxxx>
>> >> >> ---
>> >> >> x86/emulator.c | 67 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++
>> >> >> 1 file changed, 67 insertions(+)
>> >> >> mode change 100644 => 100755 x86/emulator.c
>> >> >>
>> >> >> diff --git a/x86/emulator.c b/x86/emulator.c
>> >> >> old mode 100644
>> >> >> new mode 100755
>> >> >> index 96576e5..770e8f7
>> >> >> --- a/x86/emulator.c
>> >> >> +++ b/x86/emulator.c
>> >> >> @@ -11,6 +11,13 @@ int fails, tests;
>> >> >>
>> >> >> static int exceptions;
>> >> >>
>> >> >> +struct regs {
>> >> >> + u64 rax, rbx, rcx, rdx;
>> >> >> + u64 rsi, rdi, rsp, rbp;
>> >> >> + u64 rip, rflags;
>> >> >> +};
>> >> >> +static struct regs inregs, outregs;
>> >> >> +
>> >> >> void report(const char *name, int result)
>> >> >> {
>> >> >> ++tests;
>> >> >> @@ -685,6 +692,66 @@ static void test_shld_shrd(u32 *mem)
>> >> >> report("shrd (cl)", *mem == ((0x12345678 >> 3) | (5u << 29)));
>> >> >> }
>> >> >>
>> >> >> +static void trap_emulator(uint64_t *mem, uint8_t *insn_page,
>> >> >> + uint8_t *alt_insn_page, void *insn_ram,
>> >> >> + uint8_t *alt_insn, int alt_insn_length)
>> >> >> +{
>> >> >> + ulong *cr3 = (ulong *)read_cr3();
>> >> >> + int i;
>> >> >> + static struct regs save;
>> >> >> +
>> >> >> + // Pad with RET instructions
>> >> >> + memset(insn_page, 0xc3, 4096);
>> >> >> + memset(alt_insn_page, 0xc3, 4096);
>> >> >> +
>> >> >> + // Place a trapping instruction in the page to trigger a VMEXIT
>> >> >> + insn_page[0] = 0x89; // mov %eax, (%rax)
>> >> >> + insn_page[1] = 0x00;
>> >> >> + insn_page[2] = 0x90; // nop
>> >> >> + insn_page[3] = 0xc3; // ret
>> >> >> +
>> >> >> + // Place the instruction we want the hypervisor to see in the alternate page
>> >> >> + for (i=0; i<alt_insn_length; i++)
>> >> >> + alt_insn_page[i] = alt_insn[i];
>> >> >> + save = inregs;
>> >> >> +
>> >> >> + // Load the code TLB with insn_page, but point the page tables at
>> >> >> + // alt_insn_page (and keep the data TLB clear, for AMD decode assist).
>> >> >> + // This will make the CPU trap on the insn_page instruction but the
>> >> >> + // hypervisor will see alt_insn_page.
>> >> >> + install_page(cr3, virt_to_phys(insn_page), insn_ram);
>> >> >> + invlpg(insn_ram);
>> >> >> + // Load code TLB
>> >> >> + asm volatile("call *%0" : : "r"(insn_ram + 3));
>> >> >> + install_page(cr3, virt_to_phys(alt_insn_page), insn_ram);
>> >> >> + // Trap, let hypervisor emulate at alt_insn_page
>> >> >> + asm volatile(
>> >> >> + "xchg %%rbx, 8+%[save] \n\t"
>> >> >> + "xchg %%rcx, 16+%[save] \n\t"
>> >> >> + "xchg %%rdx, 24+%[save] \n\t"
>> >> >> + "xchg %%rsi, 32+%[save] \n\t"
>> >> >> + "xchg %%rdi, 40+%[save] \n\t"
>> >> >> +
>> >> >> + "call *%1\n\t"
>> >> >> +
>> >> >> + "mov %%rax, 0+%[save] \n\t"
>> >> >> + "xchg %%rbx, 8+%[save] \n\t"
>> >> >> + "xchg %%rcx, 16+%[save] \n\t"
>> >> >> + "xchg %%rdx, 24+%[save] \n\t"
>> >> >> + "xchg %%rsi, 32+%[save] \n\t"
>> >> >> + "xchg %%rdi, 40+%[save] \n\t"
>> >> >> + "mov %%rsp, 48+%[save] \n\t"
>> >> >> + "mov %%rbp, 56+%[save] \n\t"
>> >> >> + /* Save RFLAGS in outregs*/
>> >> >> + "pushf \n\t"
>> >> >> + "popq 72+%[save] \n\t"
>> >> >> + : [save]"+m"(save)
>> >> >> + : "r"(insn_ram), "a"(mem)
>> >> >> + : "memory", "cc"
>> >> >> + );
>> >> >> + outregs = save;
>> >> >> +}
>> >> >> +
>> >> >> static void advance_rip_by_3_and_note_exception(struct ex_regs *regs)
>> >> >> {
>> >> >> ++exceptions;
>> >> >> --
>> >> >> 1.7.9.5
>> >> >
>> >> > --
>> >> > Gleb.
>> >>
>> >>
>> >>
>> >> --
>> >> Arthur Chunqi Li
>> >> Department of Computer Science
>> >> School of EECS
>> >> Peking University
>> >> Beijing, China
>> >
>> > --
>> > Gleb.
>>
>>
>>
>> --
>> Arthur Chunqi Li
>> Department of Computer Science
>> School of EECS
>> Peking University
>> Beijing, China
>
> --
> Gleb.
--
Arthur Chunqi Li
Department of Computer Science
School of EECS
Peking University
Beijing, China
--
To unsubscribe from this list: send the line "unsubscribe kvm" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
