Re: [Xen-devel] [PATCH v5 5/8] x86/hvm: Introduce hvm_save_cpu_msrs_one func

[Paul Durrant <Paul.Durrant@xxxxxxxxxx>]

> -----Original Message-----
> From: Alexandru Isaila [mailto:aisaila@xxxxxxxxxxxxxxx]
> Sent: 29 May 2018 15:59
> To: xen-devel@xxxxxxxxxxxxx
> Cc: Ian Jackson <Ian.Jackson@xxxxxxxxxx>; Wei Liu <wei.liu2@xxxxxxxxxx>;
> jbeulich@xxxxxxxx; Andrew Cooper <Andrew.Cooper3@xxxxxxxxxx>; Paul
> Durrant <Paul.Durrant@xxxxxxxxxx>; Alexandru Isaila
> <aisaila@xxxxxxxxxxxxxxx>
> Subject: [PATCH v5 5/8] x86/hvm: Introduce hvm_save_cpu_msrs_one func
> 
> This is used to save data from a single instance.
> 
> Signed-off-by: Alexandru Isaila <aisaila@xxxxxxxxxxxxxxx>
> ---
>  xen/arch/x86/hvm/hvm.c | 59 ++++++++++++++++++++++++++++-----------
> -----------
>  1 file changed, 33 insertions(+), 26 deletions(-)
> 
> diff --git a/xen/arch/x86/hvm/hvm.c b/xen/arch/x86/hvm/hvm.c
> index e8ecabf..4a22283 100644
> --- a/xen/arch/x86/hvm/hvm.c
> +++ b/xen/arch/x86/hvm/hvm.c
> @@ -1354,6 +1354,38 @@ static const uint32_t msrs_to_send[] = {
>  };
>  static unsigned int __read_mostly msr_count_max =
> ARRAY_SIZE(msrs_to_send);
> 
> +static int hvm_save_cpu_msrs_one(struct vcpu *v, struct hvm_msr *ctxt)
> +{
> +    unsigned int i;
> +
> +    for ( i = 0; i < ARRAY_SIZE(msrs_to_send); ++i )
> +    {
> +        uint64_t val;
> +        int rc = guest_rdmsr(v, msrs_to_send[i], &val);
> +
> +        /*
> +         * It is the programmers responsibility to ensure that
> +         * msrs_to_send[] contain generally-read/write MSRs.
> +         * X86EMUL_EXCEPTION here implies a missing feature, and that the
> +         * guest doesn't have access to the MSR.
> +         */
> +        if ( rc == X86EMUL_EXCEPTION )
> +            continue;
> +
> +        if ( rc != X86EMUL_OKAY )
> +        {
> +            ASSERT_UNREACHABLE();
> +            return -ENXIO;
> +        }
> +
> +        if ( !val )
> +           continue; /* Skip empty MSRs. */
> +        ctxt->msr[ctxt->count].index = msrs_to_send[i];
> +        ctxt->msr[ctxt->count++].val = val;
> +    }
> +    return 0;
> +}
> +
>  static int hvm_save_cpu_msrs(struct domain *d, hvm_domain_context_t
> *h)
>  {
>      struct vcpu *v;
> @@ -1370,32 +1402,7 @@ static int hvm_save_cpu_msrs(struct domain *d,
> hvm_domain_context_t *h)
>          ctxt = (struct hvm_msr *)&h->data[h->cur];
>          ctxt->count = 0;
> 
> -        for ( i = 0; i < ARRAY_SIZE(msrs_to_send); ++i )
> -        {
> -            uint64_t val;
> -            int rc = guest_rdmsr(v, msrs_to_send[i], &val);
> -
> -            /*
> -             * It is the programmers responsibility to ensure that
> -             * msrs_to_send[] contain generally-read/write MSRs.
> -             * X86EMUL_EXCEPTION here implies a missing feature, and that the
> -             * guest doesn't have access to the MSR.
> -             */
> -            if ( rc == X86EMUL_EXCEPTION )
> -                continue;
> -
> -            if ( rc != X86EMUL_OKAY )
> -            {
> -                ASSERT_UNREACHABLE();
> -                return -ENXIO;
> -            }
> -
> -            if ( !val )
> -                continue; /* Skip empty MSRs. */
> -
> -            ctxt->msr[ctxt->count].index = msrs_to_send[i];
> -            ctxt->msr[ctxt->count++].val = val;
> -        }
> +        hvm_save_cpu_msrs_one(v, ctxt);

No check for the return value here means you're not going to propagate a 
potential -ENXIO.

  Paul

> 
>          if ( hvm_funcs.save_msr )
>              hvm_funcs.save_msr(v, ctxt);
> --
> 2.7.4


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