Re: [PATCH v2 2/3] KVM: emulator: emulate XLAT

Paolo Bonzini
2013-05-09T11:40:38Z

Il 09/05/2013 12:03, Gleb Natapov ha scritto:
> On Thu, May 09, 2013 at 11:32:50AM +0200, Paolo Bonzini wrote:
>> This is used by SGABIOS, KVM breaks with emulate_invalid_guest_state=1.
>> It is just a MOV in disguise, with a funny source address.
>>
>> Reported-by: Jun'ichi Nomura <j-nomura@ce.jp.nec.com>
>> Cc: stable@vger.kernel.org # 3.9
>> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
>> ---
>> arch/x86/kvm/emulate.c | 16 +++++++++++++++-
>> 1 file changed, 15 insertions(+), 1 deletion(-)
>>
>> diff --git a/arch/x86/kvm/emulate.c b/arch/x86/kvm/emulate.c
>> index 709ba03..210bb4e 100644
>> --- a/arch/x86/kvm/emulate.c
>> +++ b/arch/x86/kvm/emulate.c
>> @@ -60,6 +60,7 @@
>> #define OpGS 25ull /* GS */
>> #define OpMem8 26ull /* 8-bit zero extended memory operand */
>> #define OpImm64 27ull /* Sign extended 16/32/64-bit immediate */
>> +#define OpXLat 28ull /* memory at BX/EBX/RBX + zero-extended AL */
>>
>> #define OpBits 5 /* Width of operand field */
>> #define OpMask ((1ull << OpBits) - 1)
>> @@ -99,6 +100,7 @@
>> #define SrcImmUByte (OpImmUByte << SrcShift)
>> #define SrcImmU (OpImmU << SrcShift)
>> #define SrcSI (OpSI << SrcShift)
>> +#define SrcXLat (OpXLat << SrcShift)
>> #define SrcImmFAddr (OpImmFAddr << SrcShift)
>> #define SrcMemFAddr (OpMemFAddr << SrcShift)
>> #define SrcAcc (OpAcc << SrcShift)
>> @@ -3949,7 +3951,8 @@ static const struct opcode opcode_table[256] = {
>> G(Src2One | ByteOp, group2), G(Src2One, group2),
>> G(Src2CL | ByteOp, group2), G(Src2CL, group2),
>> I(DstAcc | SrcImmUByte | No64, em_aam),
>> - I(DstAcc | SrcImmUByte | No64, em_aad), N, N,
>> + I(DstAcc | SrcImmUByte | No64, em_aad), N,
>> + I(DstAcc | SrcXLat | ByteOp, em_mov),
>> /* 0xD8 - 0xDF */
>> N, E(0, &escape_d9), N, E(0, &escape_db), N, E(0, &escape_dd), N, N,
>> /* 0xE0 - 0xE7 */
>> @@ -4207,6 +4210,17 @@ static int decode_operand(struct x86_emulate_ctxt *ctxt, struct operand *op,
>> op->val = 0;
>> op->count = 1;
>> break;
>> + case OpXLat:
> Sigh, obviously this is not reusable by any other instruction. So many
> waisted transistor :(

And a precious op value too, we only have 3 left. :/

>> + op->type = OP_MEM;
>> + op->bytes = (ctxt->d & ByteOp) ? 1 : ctxt->op_bytes;
>> + op->addr.mem.ea =
>> + register_address(ctxt,
>> + reg_read(ctxt, VCPU_REGS_RBX) +
>> + (reg_read(ctxt, VCPU_REGS_RAX) & 0xff));
>> + op->addr.mem.seg = seg_override(ctxt);
>> + op->val = 0;
>> + op->count = 1;
> The count is set only for decoding that is used by string instructions.
> I can drop it while applying.

Thanks!

Paolo

>> + break;
>> case OpImmFAddr:
>> op->type = OP_IMM;
>> op->addr.mem.ea = ctxt->_eip;
>> --
>> 1.8.1.4
>>
>
> --
> Gleb.
>