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

Gleb Natapov
2013-05-09T10:03:20Z

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 :(

> + 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.

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

--
Gleb.