Re: [Xen-devel] [PATCH v5 4/7] X86: generic MSRs save/restore

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 13.12.13 at 08:50, "Liu, Jinsong" <jinsong.liu@xxxxxxxxx> wrote:

Please get your reply quoting fixed.

> --- a/xen/arch/x86/hvm/hvm.c
> +++ b/xen/arch/x86/hvm/hvm.c
> @@ -1127,10 +1127,110 @@ static int hvm_load_cpu_xsave_states(str
>      return 0;
>  }
>  
> -/* We need variable length data chunk for xsave area, hence customized
> - * declaration other than HVM_REGISTER_SAVE_RESTORE.
> +#define HVM_CPU_MSR_SIZE(cnt) offsetof(struct hvm_msr, msr[cnt])
> +static unsigned int __read_mostly msr_count_max;
> +
> +static int hvm_save_cpu_msrs(struct domain *d, hvm_domain_context_t *h)
> +{
> +    struct vcpu *v;
> +
> +    if ( !msr_count_max )
> +        return 0;
> 
> ASSERT( msr_count_mas ); ?

Right. Left from before the registration was made conditional.

> +
> +    for_each_vcpu ( d, v )
> +    {
> +        struct hvm_msr *ctxt;
> +        unsigned int i;
> +
> +        if ( _hvm_init_entry(h, CPU_MSR_CODE, v->vcpu_id,
> +                             HVM_CPU_MSR_SIZE(msr_count_max)) )
> +            return 1;
> +        ctxt = (struct hvm_msr *)&h->data[h->cur];
> +        ctxt->count = 0;
> +
> +        if ( hvm_funcs.save_msr )
> +            hvm_funcs.save_msr(v, ctxt);
> +
> +        for ( i = 0; i < ctxt->count; ++i )
> +            ctxt->msr[i]._rsvd = 0;
> 
> What _rsvd for? seems not used at the patches.

See XSA-77 and
http://lists.xenproject.org/archives/html/xen-devel/2013-12/msg01522.html 
- avoid leaking hypervisor data.

> +static int hvm_load_cpu_msrs(struct domain *d, hvm_domain_context_t *h)
> +{
> +    unsigned int i, vcpuid = hvm_load_instance(h);
> +    struct vcpu *v;
> +    const struct hvm_save_descriptor *desc;
> +    const struct hvm_msr *ctxt;
> +    int err = 0;
> +
> +    if ( vcpuid >= d->max_vcpus || (v = d->vcpu[vcpuid]) == NULL )
> +    {
> +        dprintk(XENLOG_G_ERR, "HVM restore: dom%d has no vcpu%u\n",
> +                d->domain_id, vcpuid);
> +        return -EINVAL;
> +    }
> +
> +    /* Customized checking for entry since our entry is of variable length */
> +    desc = (struct hvm_save_descriptor *)&h->data[h->cur];
> +    if ( sizeof (*desc) > h->size - h->cur)
> +    {
> +        printk(XENLOG_G_WARNING
> +               "HVM%d.%d restore: not enough data left to read MSR 
> descriptor\n",
> +               d->domain_id, vcpuid);
> +        return -ENODATA;
> +    }
> +    if ( desc->length + sizeof (*desc) > h->size - h->cur)
> +    {
> +        printk(XENLOG_G_WARNING
> +               "HVM%d.%d restore: not enough data left to read %u MSR 
> bytes\n",
> +               d->domain_id, vcpuid, desc->length);
> +        return -ENODATA;
> +    }
> +    if ( desc->length < HVM_CPU_MSR_SIZE(1) )
> +    {
> +        printk(XENLOG_G_WARNING
> +               "HVM%d.%d restore mismatch: MSR length %u < %zu\n",
> +               d->domain_id, vcpuid, desc->length, HVM_CPU_MSR_SIZE(1));
> +        return -EINVAL;
> +    }
> +
> +    h->cur += sizeof(*desc);
> +    ctxt = (struct hvm_msr *)&h->data[h->cur];
> +    h->cur += desc->length;
> +
> +    if ( desc->length != HVM_CPU_MSR_SIZE(ctxt->count) )
> +    {
> +        printk(XENLOG_G_WARNING
> +               "HVM%d.%d restore mismatch: MSR length %u != %zu\n",
> +               d->domain_id, vcpuid, desc->length,
> +               HVM_CPU_MSR_SIZE(ctxt->count));
> +        return -EOPNOTSUPP;
> +    }
> +    /* Checking finished */
> +
> +    for ( i = 0; i < ctxt->count; ++i )
> +    {
> +        if ( hvm_funcs.load_msr )
> +            err = hvm_funcs.load_msr(v, &ctxt->msr[i]);
> +        if ( err )
> +            break;
> +    }
> 
> Is it for vmx/svm specific msrs, or, will extend to generic msrs?
> If these patches are generic save/load mechanism supporting generic msrs and 
> vmx/sve specific msrs, it need update here.

In which way?

But I'll re-write this anyway, so that we don't need to handle MSRs
one by one (leveraging the _rsvd field).

> --- a/xen/include/public/arch-x86/hvm/save.h
> +++ b/xen/include/public/arch-x86/hvm/save.h
> @@ -592,9 +592,21 @@ struct hvm_tsc_adjust {
>  
>  DECLARE_HVM_SAVE_TYPE(TSC_ADJUST, 19, struct hvm_tsc_adjust);
>  
> +
> +struct hvm_msr {
> +    uint32_t count;
> +    struct hvm_one_msr {
> +        uint32_t index;
> +        uint32_t _rsvd;
> +        uint64_t val;
> +    } msr[1 /* variable size */];
> +};
> +
> +#define CPU_MSR_CODE  16
> +
> 
> It's incorrect, conflict with CPU_XSAVE_CODE and panic when 
> hvm_register_savevm(CPU_MSR_CODE, ...)
> Why not 20?

Copy-n-paste mistake. Thanks for spotting.

Jan

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