Re: [Xen-devel] [PATCH] x86/HVM: don't retain emulated insn cache when exiting back to guest

[Julien Grall <julien.grall@xxxxxxxxxx>]

Hi Jan,

I guess I have been CCed because you would like this patch is fixing the 
regression you mentioned on IRC?
Cheers,

On 12/05/2017 04:13 PM, Jan Beulich wrote:
> vio->mmio_retry is being set when a repeated string insn is being split
> up. In that case we'll exit to the guest, expecting immediate re-entry.
> Interruptions, however, may be serviced by the guest before re-entry
> from the repeated string insn. Any emulation needed in the course of
> handling the interruption must not fetch from the internally maintained
> cache.
>
> Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
>
> --- a/xen/arch/x86/hvm/emulate.c
> +++ b/xen/arch/x86/hvm/emulate.c
> @@ -2109,20 +2109,22 @@ static int _hvm_emulate_one(struct hvm_e
>   
>       vio->mmio_retry = 0;
>   
> -    rc = x86_emulate(&hvmemul_ctxt->ctxt, ops);
> -
> -    if ( rc == X86EMUL_OKAY && vio->mmio_retry )
> -        rc = X86EMUL_RETRY;
> -    if ( rc != X86EMUL_RETRY )
> +    switch ( rc = x86_emulate(&hvmemul_ctxt->ctxt, ops) )
>       {
> +    case X86EMUL_OKAY:
> +        if ( vio->mmio_retry )
> +            rc = X86EMUL_RETRY;
> +        /* fall through */
> +    default:
>           vio->mmio_cache_count = 0;
>           vio->mmio_insn_bytes = 0;
> -    }
> -    else
> -    {
> +        break;
> +
> +    case X86EMUL_RETRY:
>           BUILD_BUG_ON(sizeof(vio->mmio_insn) < sizeof(hvmemul_ctxt->insn_buf));
>           vio->mmio_insn_bytes = hvmemul_ctxt->insn_buf_bytes;
>           memcpy(vio->mmio_insn, hvmemul_ctxt->insn_buf, vio->mmio_insn_bytes);
> +        break;
>       }
>   
>       if ( hvmemul_ctxt->ctxt.retire.singlestep )
>
>
>
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