Re: [Xen-devel] [PATCH v3 08/10] tools/libxc: Rework xc_cpuid_apply_policy() to use {get, set}_cpu_policy()

[Jan Beulich <jbeulich@suse.com>]

On 25.09.2019 20:11, Andrew Cooper wrote:
> +int xc_cpuid_apply_policy(xc_interface *xch, uint32_t domid,
> +                          const uint32_t *featureset, unsigned int nr_features)
> +{
> +    int rc;
> +    xc_dominfo_t di;
> +    unsigned int i, nr_leaves, nr_msrs;
> +    xen_cpuid_leaf_t *leaves = NULL;
> +    struct cpuid_policy *p = NULL;
> +    uint32_t err_leaf = -1, err_subleaf = -1, err_msr = -1;
> +
> +    if ( xc_domain_getinfo(xch, domid, 1, &di) != 1 ||
> +         di.domid != domid )
> +    {
> +        ERROR("Failed to obtain d%d info", domid);
> +        rc = -ESRCH;
> +        goto out;
> +    }
> +
> +    rc = xc_get_cpu_policy_size(xch, &nr_leaves, &nr_msrs);
> +    if ( rc )
> +    {
> +        PERROR("Failed to obtain policy info size");
> +        rc = -errno;
> +        goto out;
> +    }
> +
> +    rc = -ENOMEM;
> +    if ( (leaves = calloc(nr_leaves, sizeof(*leaves))) == NULL ||
> +         (p = calloc(1, sizeof(*p))) == NULL )
> +        goto out;
> +
> +    /* Get the domain's default policy. */
> +    nr_msrs = 0;
> +    rc = xc_get_system_cpu_policy(xch, di.hvm ? XEN_SYSCTL_cpu_policy_hvm_default
> +                                              : XEN_SYSCTL_cpu_policy_pv_default,
> +                                  &nr_leaves, leaves, &nr_msrs, NULL);
> +    if ( rc )
> +    {
> +        PERROR("Failed to obtain %s default policy", di.hvm ? "hvm" : "pv");
> +        rc = -errno;
> +        goto out;
> +    }
> +
> +    rc = x86_cpuid_copy_from_buffer(p, leaves, nr_leaves,
> +                                    &err_leaf, &err_subleaf);
> +    if ( rc )
> +    {
> +        ERROR("Failed to deserialise CPUID (err leaf %#x, subleaf %#x) (%d = %s)",
> +              err_leaf, err_subleaf, -rc, strerror(-rc));
> +        goto out;
> +    }
> +
> +    if ( featureset )
> +    {
> +        uint32_t disabled_features[FEATURESET_NR_ENTRIES],
> +            feat[FEATURESET_NR_ENTRIES] = {};
> +        static const uint32_t deep_features[] = INIT_DEEP_FEATURES;
> +        unsigned int i, b;
> +
> +        /*
> +         * The user supplied featureset may be shorter or longer than
> +         * FEATURESET_NR_ENTRIES.  Shorter is fine, and we will zero-extend.
> +         * Longer is fine, so long as it only padded with zeros.
> +         */
> +        unsigned int user_len = min(FEATURESET_NR_ENTRIES + 0u, nr_features);
> +
> +        /* Check for truncated set bits. */
> +        rc = -EOPNOTSUPP;
> +        for ( i = user_len; i < nr_features; ++i )
> +            if ( featureset[i] != 0 )
> +                goto out;
> +
> +        memcpy(feat, featureset, sizeof(*featureset) * user_len);
> +
> +        /* Disable deep dependencies of disabled features. */
> +        for ( i = 0; i < ARRAY_SIZE(disabled_features); ++i )
> +            disabled_features[i] = ~feat[i] & deep_features[i];
> +
> +        for ( b = 0; b < sizeof(disabled_features) * CHAR_BIT; ++b )
> +        {
> +            const uint32_t *dfs;
> +
> +            if ( !test_bit(b, disabled_features) ||
> +                 !(dfs = x86_cpuid_lookup_deep_deps(b)) )
> +                continue;
> +
> +            for ( i = 0; i < ARRAY_SIZE(disabled_features); ++i )
> +            {
> +                feat[i] &= ~dfs[i];
> +                disabled_features[i] &= ~dfs[i];
> +            }
> +        }
> +
> +        cpuid_featureset_to_policy(feat, p);
> +    }
> +
> +    if ( !di.hvm )
> +    {
> +        uint32_t host_featureset[FEATURESET_NR_ENTRIES] = {};
> +        uint32_t len = ARRAY_SIZE(host_featureset);
> +
> +        rc = xc_get_cpu_featureset(xch, XEN_SYSCTL_cpu_featureset_host,
> +                                   &len, host_featureset);
> +        if ( rc )
> +        {
> +            /* Tolerate "buffer too small", as we've got the bits we need. */
> +            if ( errno == ENOBUFS )
> +                rc = 0;
> +            else
> +            {
> +                PERROR("Failed to obtain host featureset");
> +                rc = -errno;
> +                goto out;
> +            }
> +        }
> +
> +        /*
> +         * On hardware without CPUID Faulting, PV guests see real topology.
> +         * As a consequence, they also need to see the host htt/cmp fields.
> +         */
> +        p->basic.htt       = test_bit(X86_FEATURE_HTT, host_featureset);
> +        p->extd.cmp_legacy = test_bit(X86_FEATURE_CMP_LEGACY, host_featureset);
> +    }
> +    else
> +    {
> +        /*
> +         * Topology for HVM guests is entirely controlled by Xen.  For now, we
> +         * hardcode APIC_ID = vcpu_id * 2 to give the illusion of no SMT.
> +         */
> +        p->basic.htt = true;
> +        p->extd.cmp_legacy = false;
> +
> +        /*
> +         * EBX[23:16] is Maximum Logical Processors Per Package.
> +         * Update to reflect vLAPIC_ID = vCPU_ID * 2, but make sure to avoid
> +         * overflow.
> +         */
> +        if ( !(p->basic.lppp & 0x80) )
> +            p->basic.lppp *= 2;

I think you want to start the comment with "Leaf 1 EBX[23:16] ...",
as p->basic covers all basic leaves.

Additionally, while using masking instead of a relational operator
is correct here, ...

> +        switch ( p->x86_vendor )
> +        {
> +        case X86_VENDOR_INTEL:
> +            for ( i = 0; (p->cache.subleaf[i].type &&
> +                          i < ARRAY_SIZE(p->cache.raw)); ++i )
> +            {
> +                p->cache.subleaf[i].cores_per_package =
> +                    (p->cache.subleaf[i].cores_per_package << 1) | 1;
> +                p->cache.subleaf[i].threads_per_cache = 0;
> +            }
> +            break;
> +
> +        case X86_VENDOR_AMD:
> +        case X86_VENDOR_HYGON:
> +            /*
> +             * ECX[15:12] is ApicIdCoreSize.
> +             * ECX[7:0] is NumberOfCores (minus one).
> +             * Update to reflect vLAPIC_ID = vCPU_ID * 2.  But avoid
> +             * - overflow,
> +             * - going out of sync with leaf 1 EBX[23:16],
> +             * - incrementing ApicIdCoreSize when it's zero (which changes the
> +             *   meaning of bits 7:0).
> +             */
> +            if ( !(p->extd.nc & 0x80) )

... it isn't here, i.e. this isn't a correct transformation of the
recent change for Rome): If the value is 0x7f here, the value in
leaf 1 would be 0x80. An adjustment, however, needs to be done
either to both leaves, or to none of them, to keep the values in
sufficient sync (and I think you'd break Rome again otherwise, as
p->extd.nc _is_ 0x7f there). Hence the "(regs[2] & 0xffu) < 0x7fu"
check in my recent patch.

Like above I think you want to name the (extended) leaf in the
comment, as p->extd similarly covers all extended leaves.

Jan

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