linux-kernel - Re: [RFC PATCH] clocksource: hyper-v: Enable the tsc

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Date: Tue, 28 May 2024 12:16:05 +0300
From: "kirill.shutemov@...ux.intel.com" <kirill.shutemov@...ux.intel.com>
To: Dexuan Cui <decui@...rosoft.com>
Cc: Dave Hansen <dave.hansen@...el.com>, "x86@...nel.org" <x86@...nel.org>, 
	"linux-coco@...ts.linux.dev" <linux-coco@...ts.linux.dev>, "bp@...en8.de" <bp@...en8.de>, 
	"dave.hansen@...ux.intel.com" <dave.hansen@...ux.intel.com>, Haiyang Zhang <haiyangz@...rosoft.com>, 
	"hpa@...or.com" <hpa@...or.com>, KY Srinivasan <kys@...rosoft.com>, 
	"luto@...nel.org" <luto@...nel.org>, "mingo@...hat.com" <mingo@...hat.com>, 
	"peterz@...radead.org" <peterz@...radead.org>, 
	"sathyanarayanan.kuppuswamy@...ux.intel.com" <sathyanarayanan.kuppuswamy@...ux.intel.com>, "tglx@...utronix.de" <tglx@...utronix.de>, 
	"wei.liu@...nel.org" <wei.liu@...nel.org>, jason <jason@...c4.com>, 
	"mhklinux@...look.com" <mhklinux@...look.com>, "thomas.lendacky@....com" <thomas.lendacky@....com>, 
	"tytso@....edu" <tytso@....edu>, "ardb@...nel.org" <ardb@...nel.org>, 
	"linux-hyperv@...r.kernel.org" <linux-hyperv@...r.kernel.org>, "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>, 
	Tianyu Lan <Tianyu.Lan@...rosoft.com>
Subject: Re: [RFC PATCH] clocksource: hyper-v: Enable the tsc_page for a TDX
 VM in TD mode

On Fri, May 24, 2024 at 08:45:42AM +0000, Dexuan Cui wrote:
> > From: Dave Hansen <dave.hansen@...el.com>
> > Sent: Thursday, May 23, 2024 7:26 AM
> > [...]
> > On 5/22/24 19:24, Dexuan Cui wrote:
> > ...
> > > +static bool noinstr intel_cc_platform_td_l2(enum cc_attr attr)
> > > +{
> > > +	switch (attr) {
> > > +	case CC_ATTR_GUEST_MEM_ENCRYPT:
> > > +	case CC_ATTR_MEM_ENCRYPT:
> > > +		return true;
> > > +	default:
> > > +		return false;
> > > +	}
> > > +}
> > > +
> > >  static bool noinstr intel_cc_platform_has(enum cc_attr attr)
> > >  {
> > > +	if (tdx_partitioned_td_l2)
> > > +		return intel_cc_platform_td_l2(attr);
> > > +
> > >  	switch (attr) {
> > >  	case CC_ATTR_GUEST_UNROLL_STRING_IO:
> > >  	case CC_ATTR_HOTPLUG_DISABLED:
> > 
> > On its face, this _looks_ rather troubling.  It just hijacks all of the
> > attributes.  It totally bifurcates the code.  Anything that gets added
> > to intel_cc_platform_has() now needs to be considered for addition to
> > intel_cc_platform_td_l2().
> 
> Maybe the bifurcation is necessary?

I would like to keep the same code paths for all TDX guests level, if
possible.

> TD mode is different from
> Partitioned TD mode (L2), after all. Another reason for the bifurcation
> is:  currently online/offline'ing is disallowed for a TD VM, but actually
> Hyper-V is able to support CPU online/offline'ing for a TD VM in
> Partitioned TD mode (L2) -- how can we allow online/offline'ing for such
> a VM?

This is going to be fixed by kexec patchset. It was wrong to block offline
based on TDX enumeration. It has to be stopped for MADT wake up method, if
reset vector is not supported.


-- 
  Kiryl Shutsemau / Kirill A. Shutemov