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SubjectRe: [PATCH v5 04/22] x86/virt/tdx: Prevent ACPI CPU hotplug and ACPI memory hotplug
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On Wed, 2022-06-29 at 16:35 +0800, Yuan Yao wrote:
> On Fri, Jun 24, 2022 at 11:21:59PM +1200, Kai Huang wrote:
> > 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.
>
> I see below statement, for you reference:
>
> "Wherever possible, don't use preprocessor conditionals (#if, #ifdef) in .c"
> From Documentation/process/coding-style.rst, 21) Conditional Compilation.
>
> >

This is perhaps a general rule. If you take a look at existing code, you will
immediately find AMD has a #ifdef too:

static bool amd_cc_platform_has(enum cc_attr attr)
{
#ifdef CONFIG_AMD_MEM_ENCRYPT
switch (attr) {
case CC_ATTR_MEM_ENCRYPT:
return sme_me_mask;

case CC_ATTR_HOST_MEM_ENCRYPT:
return sme_me_mask && !(sev_status & MSR_AMD64_SEV_ENABLED);

case CC_ATTR_GUEST_MEM_ENCRYPT:
return sev_status & MSR_AMD64_SEV_ENABLED;

case CC_ATTR_GUEST_STATE_ENCRYPT:
return sev_status & MSR_AMD64_SEV_ES_ENABLED;

/*
* With SEV, the rep string I/O instructions need to be unrolled
* but SEV-ES supports them through the #VC handler.
*/
case CC_ATTR_GUEST_UNROLL_STRING_IO:
return (sev_status & MSR_AMD64_SEV_ENABLED) &&
!(sev_status & MSR_AMD64_SEV_ES_ENABLED);

default:
return false;
}
#else
return false;
#endif
}

So I'll leave to maintainers.

Anyway as Christoph commented I'll give up introducing new CC attributes, so
doesn't matter anymore.

--
Thanks,
-Kai


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