Re: [RFC PATCH v4 06/36] i386/tdx: Get tdx_capabilities via KVM_TDX_CAPABILITIES

[Xiaoyao Li]

On 5/23/2022 4:45 PM, Gerd Hoffmann wrote:
>    Hi,
>
> > +    do {
> > +        size = sizeof(struct kvm_tdx_capabilities) +
> > +               max_ent * sizeof(struct kvm_tdx_cpuid_config);
> > +        caps = g_malloc0(size);
> > +        caps->nr_cpuid_configs = max_ent;
> > +
> > +        r = tdx_platform_ioctl(KVM_TDX_CAPABILITIES, 0, caps);
> > +        if (r == -E2BIG) {
> > +            g_free(caps);
> > +            max_ent *= 2;
> > +        } else if (r < 0) {
> > +            error_report("KVM_TDX_CAPABILITIES failed: %s\n", strerror(-r));
> > +            exit(1);
> > +        }
> > +    }
> > +    while (r == -E2BIG);
>
> This should have a limit for the number of loop runs.

Actually, this logic is copied from get_supported_cpuid().

Anyway, I can put a maximum limit as 256 (it should be large enough) or 
maybe re-use KVM_MAX_CPUID_ENTRIES. When it gets hit, we know we need to 
update QEMU to fit with TDX on new platform.

> take care,
>    Gerd