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

[Gleb Natapov <gleb@redhat.com>]

On Wed, Jun 19, 2013 at 11:00:56PM +0800, Arthur Chunqi Li 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 			\
No need for all the defines. Put all the code into insn_page, allocate
alt_insn_page dynamically and copy the code there by memcpy.

> +	"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"			\
If you will do ".skip 31, 0x90\n\t" instead you can drop loop
that inserts nops bellow.

> +
> +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.
I prefer all the comments to be changed to /**/ style while we are at it.

> +	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

--
			Gleb.