Il 03/06/2013 12:25, Gleb Natapov ha scritto:
> On Thu, May 30, 2013 at 05:34:21PM +0200, Paolo Bonzini wrote:
>> Il 30/05/2013 16:35, Paolo Bonzini ha scritto:
>>> The x86-64 extended low-byte registers were fetched correctly from reg,
>>> but not from mod/rm.
>>>
>>> This fixes another bug in the boot of RHEL5.9 64-bit, but it is still
>>> not enough.
>>
>> Well, it is enough but it takes 2 minutes to reach the point where
>> hardware virtualization is used. It is doing a lot of stuff in
>> emulation mode because FS and GS have leftovers from the A20 test:
>>
>> FS =0000 0000000000000000 0000ffff 00009300 DPL=0 DS16 [-WA]
>> GS =ffff 00000000000ffff0 0000ffff 00009300 DPL=0 DS16 [-WA]
>>
>> 0x00000000000113be: in $0x92,%al
>> 0x00000000000113c0: or $0x2,%al
>> 0x00000000000113c2: out %al,$0x92
>> 0x00000000000113c4: xor %ax,%ax
>> 0x00000000000113c6: mov %ax,%fs
>> 0x00000000000113c8: dec %ax
>> 0x00000000000113c9: mov %ax,%gs
>> 0x00000000000113cb: inc %ax
>> 0x00000000000113cc: mov %ax,%fs:0x200
>> 0x00000000000113d0: cmp %gs:0x210,%ax
>> 0x00000000000113d5: je 0x113cb
>>
> This is 16 bit code that sets them up. So 32bit transition code does not
> reload them?
Yes. It does this:
movw $1, %ax # protected mode (PE) bit
lmsw %ax # This is it!
jmp flush_instr
flush_instr:
xorw %bx, %bx # Flag to indicate a boot
xorl %esi, %esi # Pointer to real-mode code
movw %cs, %si
subw $DELTA_INITSEG, %si
shll $4, %esi # Convert to 32-bit pointer
.byte 0x66, 0xea # prefix + jmpi-opcode
code32: .long 0x1000 # will be set to 0x100000
# for big kernels
.word __KERNEL_CS
which jumps to boot/compressed/head.S:
startup_32:
cld
cli
movl $(__KERNEL_DS), %eax
movl %eax, %ds
movl %eax, %es
movl %eax, %ss
and totally ignores fs/gs. Much later there is this (in kernel/head.S):
/*
* We don't really need to load %fs or %gs, but load them anyway
* to kill any stale realmode selectors. This allows execution
* under VT hardware.
*/
movl %eax,%fs
movl %eax,%gs
but the whole decompression is run under emulation.
Paolo
>> The DPL < RPL test fails. Any ideas? Should we introduce a new
>> intermediate value for emulate_invalid_guest_state (0=none, 1=some, 2=full)?
>>
>> Paolo
>>
>>> Cc: gnatapov@xxxxxxxxxx
>>> Cc: kvm@xxxxxxxxxxxxxxx
>>> Cc: <stable@xxxxxxxxxxxxxxx> # 3.9
>>> Signed-off-by: Paolo Bonzini <pbonzini@xxxxxxxxxx>
>>> ---
>>> arch/x86/kvm/emulate.c | 5 ++++-
>>> 1 file changed, 4 insertions(+), 1 deletion(-)
>>>
>>> diff --git a/arch/x86/kvm/emulate.c b/arch/x86/kvm/emulate.c
>>> index aa68106..028b34f 100644
>>> --- a/arch/x86/kvm/emulate.c
>>> +++ b/arch/x86/kvm/emulate.c
>>> @@ -1239,9 +1239,12 @@ static int decode_modrm(struct x86_emulate_ctxt *ctxt,
>>> ctxt->modrm_seg = VCPU_SREG_DS;
>>>
>>> if (ctxt->modrm_mod == 3) {
>>> + int highbyte_regs = ctxt->rex_prefix == 0;
>>> +
>>> op->type = OP_REG;
>>> op->bytes = (ctxt->d & ByteOp) ? 1 : ctxt->op_bytes;
>>> - op->addr.reg = decode_register(ctxt, ctxt->modrm_rm, ctxt->d & ByteOp);
>>> + op->addr.reg = decode_register(ctxt, ctxt->modrm_rm,
>>> + highbyte_regs && (ctxt->d & ByteOp));
>>> if (ctxt->d & Sse) {
>>> op->type = OP_XMM;
>>> op->bytes = 16;
>>>
>
> --
> Gleb.
>
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