I found the final reason! The initial use of init_ram is also used by
test_rip_relative(), which will cause conflict. I changed it and
everything runs well.
On Wed, Jun 19, 2013 at 8:32 PM, Gleb Natapov <gleb@xxxxxxxxxx> wrote:
> On Wed, Jun 19, 2013 at 08:30:33PM +0800, 李春奇 <Arthur Chunqi Li> wrote:
>> On Wed, Jun 19, 2013 at 8:26 PM, Gleb Natapov <gleb@xxxxxxxxxx> wrote:
>> > On Wed, Jun 19, 2013 at 08:18:29PM +0800, 李春奇 <Arthur Chunqi Li> wrote:
>> >> On Wed, Jun 19, 2013 at 5:31 PM, Gleb Natapov <gleb@xxxxxxxxxx> wrote:
>> >> > On Wed, Jun 19, 2013 at 09:26:59AM +0800, 李春奇 <Arthur Chunqi Li> wrote:
>> >> >> On Wed, Jun 19, 2013 at 12:44 AM, Gleb Natapov <gleb@xxxxxxxxxx> wrote:
>> >> >> > Send code in a form of a patch.
>> >> >> >
>> >> >> > On Wed, Jun 19, 2013 at 12:14:13AM +0800, 李春奇 <Arthur Chunqi Li> wrote:
>> >> >> >> extern u8 insn_page[], insn_page_end[];
>> >> >> >> extern u8 test_insn[], test_insn_end[];
>> >> >> >> extern u8 alt_insn_page[];
>> >> >> >>
>> >> >> >> asm(
>> >> >> >> ".align 4096\n\t"
>> >> >> >> ".global insn_page\n\t"
>> >> >> >> ".global insn_page_end\n\t"
>> >> >> >> ".global test_insn\n\t"
>> >> >> >> ".global test_insn_end\n\t"
>> >> >> >> "insn_page:\n\t"
>> >> >> >>
>> >> >> >> "ret \n\t"
>> >> >> >>
>> >> >> >> "push %rax; push %rbx\n\t"
>> >> >> >> "push %rcx; push %rdx\n\t"
>> >> >> >> "push %rsi; push %rdi\n\t"
>> >> >> >> "push %rbp\n\t"
>> >> >> >> "push %r8; push %r9\n\t"
>> >> >> >> "push %r10; push %r11\n\t"
>> >> >> >> "push %r12; push %r13\n\t"
>> >> >> >> "push %r14; push %r15\n\t"
>> >> >> >> "pushf\n\t"
>> >> >> >>
>> >> >> >> "push 136+save \n\t"
>> >> >> >> "popf \n\t"
>> >> >> >> "mov 0+save, %rax \n\t"
>> >> >> >> "mov 8+save, %rbx \n\t"
>> >> >> >> "mov 16+save, %rcx \n\t"
>> >> >> >> "mov 24+save, %rdx \n\t"
>> >> >> >> "mov 32+save, %rsi \n\t"
>> >> >> >> "mov 40+save, %rdi \n\t"
>> >> >> >> "mov 56+save, %rbp \n\t"
>> >> >> >> "mov 64+save, %r8 \n\t"
>> >> >> >> "mov 72+save, %r9 \n\t"
>> >> >> >> "mov 80+save, %r10 \n\t"
>> >> >> >> "mov 88+save, %r11 \n\t"
>> >> >> >> "mov 96+save, %r12 \n\t"
>> >> >> >> "mov 104+save, %r13 \n\t"
>> >> >> >> "mov 112+save, %r14 \n\t"
>> >> >> >> "mov 120+save, %r15 \n\t"
>> >> >> >>
>> >> >> >> "test_insn:\n\t"
>> >> >> >> "in (%dx),%al\n\t"
>> >> >> >> ". = . + 31\n\t"
>> >> >> >> "test_insn_end:\n\t"
>> >> >> >>
>> >> >> >> "pushf \n\t"
>> >> >> >> "pop 136+save \n\t"
>> >> >> >> "mov %rax, 0+save \n\t"
>> >> >> >> "mov %rbx, 8+save \n\t"
>> >> >> >> "mov %rcx, 16+save \n\t"
>> >> >> >> "mov %rdx, 24+save \n\t"
>> >> >> >> "mov %rsi, 32+save \n\t"
>> >> >> >> "mov %rdi, 40+save \n\t"
>> >> >> >> "mov %rbp, 56+save \n\t"
>> >> >> >> "mov %r8, 64+save \n\t"
>> >> >> >> "mov %r9, 72+save \n\t"
>> >> >> >> "mov %r10, 80+save \n\t"
>> >> >> >> "mov %r11, 88+save \n\t"
>> >> >> >> "mov %r12, 96+save \n\t"
>> >> >> >> "mov %r13, 104+save \n\t"
>> >> >> >> "mov %r14, 112+save \n\t"
>> >> >> >> "mov %r15, 120+save \n\t"
>> >> >> >> "popf \n\t"
>> >> >> >> "pop %r15; pop %r14 \n\t"
>> >> >> >> "pop %r13; pop %r12 \n\t"
>> >> >> >> "pop %r11; pop %r10 \n\t"
>> >> >> >> "pop %r9; pop %r8 \n\t"
>> >> >> >> "pop %rbp \n\t"
>> >> >> >> "pop %rdi; pop %rsi \n\t"
>> >> >> >> "pop %rdx; pop %rcx \n\t"
>> >> >> >> "pop %rbx; pop %rax \n\t"
>> >> >> >>
>> >> >> >> "ret\n\t"
>> >> >> >> "save:\n\t"
>> >> >> >> ". = . + 256\n\t"
>> >> >> >> ".align 4096\n\t"
>> >> >> >> "alt_insn_page:\n\t"
>> >> >> >> ". = . + 4096\n\t"
>> >> >> >> );
>> >> >> >>
>> >> >> >>
>> >> >> >> static void mk_insn_page(uint8_t *alt_insn_page,
>> >> >> >> uint8_t *alt_insn, int alt_insn_length)
>> >> >> >> {
>> >> >> >> int i, emul_offset;
>> >> >> >> for (i=1; i<test_insn_end - test_insn; i++)
>> >> >> >> test_insn[i] = 0x90; // nop
>> >> >> > Why? Gcc should pad it with nops.
>> >> >> >
>> >> >> >> emul_offset = test_insn - insn_page;
>> >> >> >> for (i=0; i<alt_insn_length; i++)
>> >> >> >> alt_insn_page[i+emul_offset] = alt_insn[i];
>> >> >> >> }
>> >> >> >>
>> >> >> >> static void trap_emulator(uint64_t *mem, uint8_t* alt_insn, int alt_insn_length)
>> >> >> >> {
>> >> >> >> ulong *cr3 = (ulong *)read_cr3();
>> >> >> >> int save_offset = (u8 *)(&save) - insn_page;
>> >> >> >>
>> >> >> >> memset(alt_insn_page, 0x90, 4096);
>> >> >> > alt_insn_page should contains the same instruction as insn_page except
>> >> >> > between test_insn and test_insn_end. I do not know how you expect it to
>> >> >> > work otherwise.
>> >> >> In my oponion, only codes between test_insn and test_insn_end in
>> >> >> alt_insn_page need to be set, insn_page will be executed in the guest,
>> >> >> and when trapping into emulator OS will load alt_insn_page (because of
>> >> >> invlpg(insn_page)), then return to guest with executing insn_page
>> >> >> (from TLB).
>> >> > While before trap the code will likely be executed from insn_page,
>> >> > but after the trap it is very optimistic to assume that tlb cache
>> >> > will still contain this virtual address since host will execute quite a
>> >> > lot of code and can even schedule in the middle, so the TLB will not
>> >> > contain the address and your test will crash. Even the code before test
>> >> > instruction can be executed from alt_insn_page if guest is scheduled out
>> >> > after invlpg() and before it executes every instruction until trapping
>> >> > one. In your case the test will crash too instead of yielding false positive.
>> >> >
>> >> >> I don't know if this is right, but I use this trick in my
>> >> >> previous patch and it runs well.
>> >> > Your previous patches always had c3 (ret) after tested instruction on
>> >> > alt_insn_page.
>> >> >
>> >> >> I use "trace-cmd record -e kvm" to
>> >> >> trace it and found instructions in alt_insn_page are not executed, so
>> >> >> I suppose that alt_insn_page is not loaded to the right place.
>> >> > Do you see "in" instruction emulated? Anyway current code is incorrect
>> >> > since current install_page() implementation cannot handle large pages
>> >> > and the code is backed up by large pages. You can fix install_page() to
>> >> > check for that and break large page into small one before installing a
>> >> > page.
>> >> Here I have two questions.
>> >> 1. There's another function called "install_large_page", can it be
>> >> used to our occasion? I found that this function is not used at all.
>> > It is used when initial page tables are created.
>> > See lib/x86/vm.c:setup_mmu_range()
>> >
>> >> 2. Why will current version runs well? Do pages allocated dynamically
>> >> are automatically aligned to 2MB (large page size)?
>> >>
>> > No, they are 4K pages.
>> Thus why dynamically creating insn_page and alt_insn_page with
>> alloc_page() can get the right result?
> Probably.
>
> --
> Gleb.
--
Arthur Chunqi Li
Department of Computer Science
School of EECS
Peking University
Beijing, China
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