On 03/03/20 14:02, Vitaly Kuznetsov wrote:
> Right you are,
>
> a big hammer like
>
> diff --git a/arch/x86/include/asm/kvm_emulate.h b/arch/x86/include/asm/kvm_emulate.h
> index 2a8f2bd..52c9bce 100644
> --- a/arch/x86/include/asm/kvm_emulate.h
> +++ b/arch/x86/include/asm/kvm_emulate.h
> @@ -324,14 +324,6 @@ struct x86_emulate_ctxt {
> */
>
> /* current opcode length in bytes */
> - u8 opcode_len;
> - u8 b;
> - u8 intercept;
> - u8 op_bytes;
> - u8 ad_bytes;
> - struct operand src;
> - struct operand src2;
> - struct operand dst;
> union {
> int (*execute)(struct x86_emulate_ctxt *ctxt);
> fastop_t fop;
> @@ -343,6 +335,14 @@ struct x86_emulate_ctxt {
> * or elsewhere
> */
> bool rip_relative;
> + u8 opcode_len;
> + u8 b;
> + u8 intercept;
> + u8 op_bytes;
> + u8 ad_bytes;
> + struct operand src;
> + struct operand src2;
> + struct operand dst;
> u8 rex_prefix;
> u8 lock_prefix;
> u8 rep_prefix;
>
> seems to make the issue go away. (For those wondering why fielf
> shuffling makes a difference: init_decode_cache() clears
> [rip_relative, modrm) range) How did this even work before...
> (I'm still looking at the code, stay tuned...)
On AMD, probably because all these instructions were normally trapped by L1.
Of these, however, most need not be zeroed again. op_bytes, ad_bytes,
opcode_len and b are initialized by x86_decode_insn, and dst/src/src2
also by decode_operand. So only intercept is affected, adding
"ctxt->intercept = x86_intercept_none" should be enough.
Paolo
