Re: [PATCH 1/2] kvm-unit-tests: Add a func to run instruction in emulator

[Gleb Natapov <gleb@redhat.com>]

On Thu, Jun 20, 2013 at 10:29:42AM +0200, Paolo Bonzini wrote:
> Il 19/06/2013 18:03, Gleb Natapov ha scritto:
> > On Wed, Jun 19, 2013 at 11:07:18PM +0800, 李春奇 <Arthur Chunqi Li> wrote:
> >> Hi Gleb,
> >> This version can set %rsp before trapping into emulator, because
> >> insn_page and alt_insn_page is statically defined and their relative
> >> position to (save) is fixed during execution.
> >>
> > The position of the code is not fixed during execution since you execute
> > it from a virtual address obtained dynamically by vmap() and the address
> > is definitely different from the one the code was compiled for, but if
> > you look at the code that compile actually produce you will see that it
> > uses absolute address to access "save" and this is why it works. I
> > wounder why compiler decided to use absolute address this time, Paolo?
> 
> Because he's using assembly with operands that he wrote himself.  Before
> he was using "m" and the compiler decided to express the memory operand
> as "save(%rip)".
> 
> The assembler then emits different opcodes (of course) and also
> different relocations.  In the current code, it tells the linker to
> place an absolute address.  In the previous one, it tells the linker to
> place a delta from %rip.
> 
Heh, make sense. OK, so we will go with that. Will comment on the patch
itself.

> Paolo
> 
> >> In this way, test case of test_mmx_movq_mf needs to pre-define its own
> >> stack, this change is in the next patch.
> >>
> >> In this version, insn_ram is initially mapped to insn_page and them
> >> each call to insn_page/alt_insn_page are all via insn_ram. This trick
> >> runs well but I don't know why my previous version causes error.
> >>
> > Because previous version tried to use install_page() on a large page
> > mapped region and the function does not know how to handle that.
> > 
> >> Arthur.
> >> On Wed, Jun 19, 2013 at 11:00 PM, Arthur Chunqi Li <yzt356@gmail.com> wrote:
> >>> Add a function trap_emulator to run an instruction in emulator.
> >>> Set inregs first (%rax is invalid because it is used as return
> >>> address), put instruction codec in alt_insn and call func with
> >>> alt_insn_length. Get results in outregs.
> >>>
> >>> Signed-off-by: Arthur Chunqi Li <yzt356@gmail.com>
> >>> ---
> >>>  x86/emulator.c |  110 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++
> >>>  1 file changed, 110 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..48d45c8
> >>> --- a/x86/emulator.c
> >>> +++ b/x86/emulator.c
> >>> @@ -11,6 +11,15 @@ int fails, tests;
> >>>
> >>>  static int exceptions;
> >>>
> >>> +struct regs {
> >>> +       u64 rax, rbx, rcx, rdx;
> >>> +       u64 rsi, rdi, rsp, rbp;
> >>> +       u64 r8, r9, r10, r11;
> >>> +       u64 r12, r13, r14, r15;
> >>> +       u64 rip, rflags;
> >>> +};
> >>> +struct regs inregs, outregs, save;
> >>> +
> >>>  void report(const char *name, int result)
> >>>  {
> >>>         ++tests;
> >>> @@ -685,6 +694,107 @@ static void test_shld_shrd(u32 *mem)
> >>>      report("shrd (cl)", *mem == ((0x12345678 >> 3) | (5u << 29)));
> >>>  }
> >>>
> >>> +#define INSN_SAVE                      \
> >>> +       "ret\n\t"                               \
> >>> +       "pushf\n\t"                     \
> >>> +       "push 136+save \n\t"            \
> >>> +       "popf \n\t"                     \
> >>> +       "xchg %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"               \
> >>> +       "xchg %rsp, 48+save \n\t"               \
> >>> +       "xchg %rbp, 56+save \n\t"               \
> >>> +       "xchg %r8, 64+save \n\t"                \
> >>> +       "xchg %r9, 72+save \n\t"                \
> >>> +       "xchg %r10, 80+save \n\t"               \
> >>> +       "xchg %r11, 88+save \n\t"               \
> >>> +       "xchg %r12, 96+save \n\t"               \
> >>> +       "xchg %r13, 104+save \n\t"              \
> >>> +       "xchg %r14, 112+save \n\t"              \
> >>> +       "xchg %r15, 120+save \n\t"              \
> >>> +
> >>> +#define INSN_RESTORE                   \
> >>> +       "xchg %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"               \
> >>> +       "xchg %rsp, 48+save \n\t"               \
> >>> +       "xchg %rbp, 56+save \n\t"               \
> >>> +       "xchg %r8, 64+save \n\t"                \
> >>> +       "xchg %r9, 72+save \n\t"                \
> >>> +       "xchg %r10, 80+save \n\t"               \
> >>> +       "xchg %r11, 88+save \n\t"               \
> >>> +       "xchg %r12, 96+save \n\t"               \
> >>> +       "xchg %r13, 104+save \n\t"              \
> >>> +       "xchg %r14, 112+save \n\t"              \
> >>> +       "xchg %r15, 120+save \n\t"              \
> >>> +       "pushf \n\t"                    \
> >>> +       "pop 136+save \n\t"             \
> >>> +       "popf \n\t"                     \
> >>> +       "ret \n\t"                              \
> >>> +
> >>> +#define INSN_TRAP                      \
> >>> +       "in  (%dx),%al\n\t"                     \
> >>> +       ". = . + 31\n\t"                        \
> >>> +
> >>> +asm(
> >>> +       ".align 4096\n\t"
> >>> +       "insn_page:\n\t"
> >>> +       INSN_SAVE
> >>> +       "test_insn:\n\t"
> >>> +       INSN_TRAP
> >>> +       "test_insn_end:\n\t"
> >>> +       INSN_RESTORE
> >>> +       "insn_page_end:\n\t"
> >>> +       ".align 4096\n\t"
> >>> +
> >>> +       "alt_insn_page:\n\t"
> >>> +       INSN_SAVE
> >>> +       "alt_test_insn:\n\t"
> >>> +       INSN_TRAP
> >>> +       "alt_test_insn_end:\n\t"
> >>> +       INSN_RESTORE
> >>> +       "alt_insn_page_end:\n\t"
> >>> +       ".align 4096\n\t"
> >>> +);
> >>> +
> >>> +static void trap_emulator(uint64_t *mem, uint8_t* alt_insn, int alt_insn_length)
> >>> +{
> >>> +       ulong *cr3 = (ulong *)read_cr3();
> >>> +       void *insn_ram;
> >>> +       int i;
> >>> +       extern u8 insn_page[], test_insn[], test_insn_end[];
> >>> +       extern u8 alt_insn_page[], alt_test_insn[];
> >>> +
> >>> +       insn_ram = vmap(virt_to_phys(insn_page), 4096);
> >>> +       for (i=1; i<test_insn_end - test_insn; i++)
> >>> +               alt_test_insn[i] = test_insn[i] = 0x90; // nop
> >>> +       for (i=0; i<alt_insn_length; i++)
> >>> +               alt_test_insn[i] = alt_insn[i];
> >>> +       for(;i<test_insn_end - test_insn; i++)
> >>> +               alt_test_insn[i] = 0x90; // nop
> >>> +       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));
> >>> +       install_page(cr3, virt_to_phys(alt_insn_page), insn_ram);
> >>> +       // Trap, let hypervisor emulate at alt_insn_page
> >>> +       asm volatile("call *%0": : "r"(insn_ram+1));
> >>> +
> >>> +       outregs = save;
> >>> +}
> >>> +
> >>>  static void advance_rip_by_3_and_note_exception(struct ex_regs *regs)
> >>>  {
> >>>      ++exceptions;
> >>> --
> >>> 1.7.9.5
> >>>
> >>
> >>
> >>
> >> --
> >> Arthur Chunqi Li
> >> Department of Computer Science
> >> School of EECS
> >> Peking University
> >> Beijing, China
> > 
> > --
> > 			Gleb.
> > --
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> > 

--
			Gleb.