Re: [Qemu-devel] Guest SIGILL when different IO is implemented

[Paolo Bonzini]

On 11/05/2017 14:40, Miltiadis Hatzimihail wrote:
> Thanks Paolo that worked!
> 
> Btw, this line
> 
> ​
> +       GP(SrcMem | DstReg | ModRM | Mov, &pfx_0f_10_0f_11),
> +       GP(SrcReg | DstMem | ModRM | Mov, &pfx_0f_10_0f_11),
> -        N, N, N, N, N, N, N, N,
> +       N, N, N, N, N, N,
> 
> I think it has 2 extra Ns (not removed from your change?).

Oops, you're right.

> Those instructions were not implemented for a reason or is it simply a
> chance of never seeing this issue that I saw?

Never seeing this issue.

>>> The interesting thing is that in the ram case the test is passing, but in
>>> the io is failing. Also, if I try this without KVM, it passes in both cases.
>>
>>Yes, in the RAM case KVM is not invoked at all.
> So for my benefit, does this mean that any RAM transaction is emulated
> by QEMU or does it go through KVM to the bare metal? (and hence, KVM is
> not emulating this?)

The latter.  The don't get any emulation.

Paolo

> 
> ​Milton
> 
> 
> On Thu, May 11, 2017 at 12:51 PM, Paolo Bonzini <address@hidden
> <mailto:address@hidden>> wrote:
> 
> 
> 
>     On 11/05/2017 09:00, Miltiadis Hatzimihail wrote:
>     >
>     > The interesting thing is that in the ram case the test is passing, but 
> in
>     > the io is failing. Also, if I try this without KVM, it passes in both 
> cases.
> 
>     Yes, in the RAM case KVM is not invoked at all.
> 
>     > So I ve done some reading and for the 2 cases above I get:
>     >
>     > - KVM_EXIT_MMIO on memory_region_init_io  (KVM attempts and fails to
>     > emulate MOVSS),
>     > - KVM_EXIT_EXCEPTION on memory_region_init_ram(QEMU emulates MOVSS)
> 
>     No, you don't get any exit for memory_region_init_ram.
> 
>     > Is that right?
>     >
>     > Now the question is, if I want to use the IO instead of a RAM, what's 
> the
>     > best way to solve this?
> 
>     Please try this KVM patch:
> 
>     diff --git a/arch/x86/kvm/emulate.c b/arch/x86/kvm/emulate.c
>     index c25cfaf584e7..53fbd1589d2e 100644
>     --- a/arch/x86/kvm/emulate.c
>     +++ b/arch/x86/kvm/emulate.c
>     @@ -3534,6 +3534,22 @@ static int em_rdpmc(struct x86_emulate_ctxt
>     *ctxt)
>             return X86EMUL_CONTINUE;
>      }
> 
>     +static int em_movss(struct x86_emulate_ctxt *ctxt)
>     +{
>     +       memcpy(ctxt->dst.valptr, ctxt->src.valptr, 4);
>     +       ctxt->op_bytes = 4;
>     +       ctxt->dst.bytes = 4;
>     +       return X86EMUL_CONTINUE;
>     +}
>     +
>     +static int em_movsd(struct x86_emulate_ctxt *ctxt)
>     +{
>     +       memcpy(ctxt->dst.valptr, ctxt->src.valptr, 8);
>     +       ctxt->op_bytes = 8;
>     +       ctxt->dst.bytes = 8;
>     +       return X86EMUL_CONTINUE;
>     +}
>     +
>      static int em_mov(struct x86_emulate_ctxt *ctxt)
>      {
>             memcpy(ctxt->dst.valptr, ctxt->src.valptr,
>     sizeof(ctxt->src.valptr));
>     @@ -4407,6 +4423,11 @@ static int check_perm_out(struct
>     x86_emulate_ctxt *ctxt)
>             I(Mmx, em_mov), I(Sse | Aligned, em_mov), N, I(Sse |
>     Unaligned, em_mov),
>      };
> 
>     +static const struct gprefix pfx_0f_10_0f_11 = {
>     +       I(Sse | Unaligned, em_mov), I(Sse | Unaligned, em_mov),
>     +       I(Sse, em_movsd), I(Sse, em_movss),
>     +};
>     +
>      static const struct instr_dual instr_dual_0f_2b = {
>             I(0, em_mov), N
>      };
>     @@ -4626,6 +4647,8 @@ static int check_perm_out(struct
>     x86_emulate_ctxt *ctxt)
>             DI(ImplicitOps | Priv, invd), DI(ImplicitOps | Priv,
>     wbinvd), N, N,
>             N, D(ImplicitOps | ModRM | SrcMem | NoAccess), N, N,
>             /* 0x10 - 0x1F */
>     ​​
>     +       GP(SrcMem | DstReg | ModRM | Mov, &pfx_0f_10_0f_11),
>     +       GP(SrcReg | DstMem | ModRM | Mov, &pfx_0f_10_0f_11),
>             N, N, N, N, N, N, N, N,
>             D(ImplicitOps | ModRM | SrcMem | NoAccess),
>             N, N, N, N, N, N, D(ImplicitOps | ModRM | SrcMem | NoAccess),
> 
>     Thanks,
> 
>     Paolo
> 
>