Subject: Re: [PATCH v3 5/7] KVM: PPC: reimplements LOAD_VSX/STORE_VSX instruction mmio emulation with analyse_intr() input

From: Simon Guo <[email-masked]>
Date: Wed, 23 May 2018 11:06:46 +0800

Hi Paul,
On Tue, May 22, 2018 at 07:41:51PM +1000, Paul Mackerras wrote:
> On Mon, May 21, 2018 at 01:24:24PM +0800, [email-masked] wrote:
> > From: Simon Guo <[email-masked]>
> > 
> > This patch reimplements LOAD_VSX/STORE_VSX instruction MMIO emulation with
> > analyse_intr() input. It utilizes VSX_FPCONV/VSX_SPLAT/SIGNEXT exported
> > by analyse_instr() and handle accordingly.
> > 
> > When emulating VSX store, the VSX reg will need to be flushed so that
> > the right reg val can be retrieved before writing to IO MEM.
> 
> When I tested this patch set with the MMIO emulation test program I
> have, I got a host crash on the first test that used a VSX instruction
> with a register number >= 32, that is, a VMX register.  The crash was
> that it hit the BUG() at line 1193 of arch/powerpc/kvm/powerpc.c.
> 
> The reason it hit the BUG() is that vcpu->arch.io_gpr was 0xa3.
> What's happening here is that analyse_instr gives a register numbers
> in the range 32 - 63 for VSX instructions which access VMX registers.
> When 35 is ORed with 0x80 (KVM_MMIO_REG_VSX) we get 0xa3.
> 
> The old code didn't pass the high bit of the register number to
> kvmppc_handle_vsx_load/store, but instead passed it via the
> vcpu->arch.mmio_vsx_tx_sx_enabled field.  With your patch set we still
> set and use that field, so the patch below on top of your patches is
> the quick fix.  Ideally we would get rid of that field and just use
> the high (0x20) bit of the register number instead, but that can be
> cleaned up later.
> 
> If you like, I will fold the patch below into this patch and push the
> series to my kvm-ppc-next branch.
> 
> Paul.
Sorry my test missed this kind of cases. Please go ahead to fold the patch
as you suggested.  Thanks for point it out.

If you like, I can do the clean up work. If I understand correctly,
we need to expand io_gpr to u16 from u8 so that reg number can use 
6 bits and leave room for other reg flag bits.

BR,
- Simon

> ---
> diff --git a/arch/powerpc/kvm/emulate_loadstore.c b/arch/powerpc/kvm/emulate_loadstore.c
> index 0165fcd..afde788 100644
> --- a/arch/powerpc/kvm/emulate_loadstore.c
> +++ b/arch/powerpc/kvm/emulate_loadstore.c
> @@ -242,8 +242,8 @@ int kvmppc_emulate_loadstore(struct kvm_vcpu *vcpu)
>  			}
>  
>  			emulated = kvmppc_handle_vsx_load(run, vcpu,
> -					KVM_MMIO_REG_VSX|op.reg, io_size_each,
> -					1, op.type & SIGNEXT);
> +					KVM_MMIO_REG_VSX | (op.reg & 0x1f),
> +					io_size_each, 1, op.type & SIGNEXT);
>  			break;
>  		}
>  #endif
> @@ -363,7 +363,7 @@ int kvmppc_emulate_loadstore(struct kvm_vcpu *vcpu)
>  			}
>  
>  			emulated = kvmppc_handle_vsx_store(run, vcpu,
> -					op.reg, io_size_each, 1);
> +					op.reg & 0x1f, io_size_each, 1);
>  			break;
>  		}
>  #endif