linux-kernel - Re: [PATCH v5 04/22] x86/virt/tdx: Prevent ACPI CPU hotplug and ACPI memory hotplug

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Date:   Fri, 24 Jun 2022 23:21:59 +1200
From:   Kai Huang <kai.huang@...el.com>
To:     Chao Gao <chao.gao@...el.com>
Cc:     linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
        seanjc@...gle.com, pbonzini@...hat.com, dave.hansen@...el.com,
        len.brown@...el.com, tony.luck@...el.com,
        rafael.j.wysocki@...el.com, reinette.chatre@...el.com,
        dan.j.williams@...el.com, peterz@...radead.org, ak@...ux.intel.com,
        kirill.shutemov@...ux.intel.com,
        sathyanarayanan.kuppuswamy@...ux.intel.com,
        isaku.yamahata@...el.com, thomas.lendacky@....com,
        Tianyu.Lan@...rosoft.com
Subject: Re: [PATCH v5 04/22] x86/virt/tdx: Prevent ACPI CPU hotplug and
 ACPI memory hotplug

On Fri, 2022-06-24 at 09:41 +0800, Chao Gao wrote:
> On Wed, Jun 22, 2022 at 11:16:07PM +1200, Kai Huang wrote:
> > -static bool intel_cc_platform_has(enum cc_attr attr)
> > +#ifdef CONFIG_INTEL_TDX_GUEST
> > +static bool intel_tdx_guest_has(enum cc_attr attr)
> > {
> > 	switch (attr) {
> > 	case CC_ATTR_GUEST_UNROLL_STRING_IO:
> > @@ -28,6 +31,33 @@ static bool intel_cc_platform_has(enum cc_attr attr)
> > 		return false;
> > 	}
> > }
> > +#endif
> > +
> > +#ifdef CONFIG_INTEL_TDX_HOST
> > +static bool intel_tdx_host_has(enum cc_attr attr)
> > +{
> > +	switch (attr) {
> > +	case CC_ATTR_ACPI_CPU_HOTPLUG_DISABLED:
> > +	case CC_ATTR_ACPI_MEMORY_HOTPLUG_DISABLED:
> > +		return true;
> > +	default:
> > +		return false;
> > +	}
> > +}
> > +#endif
> > +
> > +static bool intel_cc_platform_has(enum cc_attr attr)
> > +{
> > +#ifdef CONFIG_INTEL_TDX_GUEST
> > +	if (boot_cpu_has(X86_FEATURE_TDX_GUEST))
> > +		return intel_tdx_guest_has(attr);
> > +#endif
> > +#ifdef CONFIG_INTEL_TDX_HOST
> > +	if (platform_tdx_enabled())
> > +		return intel_tdx_host_has(attr);
> > +#endif
> > +	return false;
> > +}
> 
> how about:
> 
> static bool intel_cc_platform_has(enum cc_attr attr)
> {
> 	switch (attr) {
> 	/* attributes applied to TDX guest only */
> 	case CC_ATTR_GUEST_UNROLL_STRING_IO:
> 	...
> 		return boot_cpu_has(X86_FEATURE_TDX_GUEST);
> 
> 	/* attributes applied to TDX host only */
> 	case CC_ATTR_ACPI_CPU_HOTPLUG_DISABLED:
> 	case CC_ATTR_ACPI_MEMORY_HOTPLUG_DISABLED:
> 		return platform_tdx_enabled();
> 
> 	default:
> 		return false;
> 	}
> }
> 
> so that we can get rid of #ifdef/endif.

Personally I don't quite like this way.  To me having separate function for host
and guest is more clear and more flexible.  And I don't think having
#ifdef/endif has any problem.  I would like to leave to maintainers.

-- 
Thanks,
-Kai