linux-kernel - RE: [PATCH v6 2/5] x86/cpufeatures: Add X86_FEATURE_SGX

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Message-ID: <DM8PR11MB5750B00C4B5D5ECB6FD7BBFDE798A@DM8PR11MB5750.namprd11.prod.outlook.com>
Date: Fri, 23 May 2025 06:35:11 +0000
From: "Reshetova, Elena" <elena.reshetova@...el.com>
To: "Huang, Kai" <kai.huang@...el.com>, "Hansen, Dave" <dave.hansen@...el.com>
CC: "Raynor, Scott" <scott.raynor@...el.com>, "seanjc@...gle.com"
	<seanjc@...gle.com>, "mingo@...nel.org" <mingo@...nel.org>, "Scarlata,
 Vincent R" <vincent.r.scarlata@...el.com>, "x86@...nel.org" <x86@...nel.org>,
	"jarkko@...nel.org" <jarkko@...nel.org>, "Annapurve, Vishal"
	<vannapurve@...gle.com>, "linux-kernel@...r.kernel.org"
	<linux-kernel@...r.kernel.org>, "Mallick, Asit K" <asit.k.mallick@...el.com>,
	"Aktas, Erdem" <erdemaktas@...gle.com>, "Cai, Chong" <chongc@...gle.com>,
	"bondarn@...gle.com" <bondarn@...gle.com>, "linux-sgx@...r.kernel.org"
	<linux-sgx@...r.kernel.org>, "dionnaglaze@...gle.com"
	<dionnaglaze@...gle.com>
Subject: RE: [PATCH v6 2/5] x86/cpufeatures: Add X86_FEATURE_SGX_EUPDATESVN
 feature flag

> -----Original Message-----
> From: Huang, Kai <kai.huang@...el.com>
> Sent: Friday, May 23, 2025 3:18 AM
> To: Reshetova, Elena <elena.reshetova@...el.com>; Hansen, Dave
> <dave.hansen@...el.com>
> Cc: Raynor, Scott <scott.raynor@...el.com>; seanjc@...gle.com;
> mingo@...nel.org; Scarlata, Vincent R <vincent.r.scarlata@...el.com>;
> x86@...nel.org; jarkko@...nel.org; Annapurve, Vishal
> <vannapurve@...gle.com>; linux-kernel@...r.kernel.org; Mallick, Asit K
> <asit.k.mallick@...el.com>; Aktas, Erdem <erdemaktas@...gle.com>; Cai,
> Chong <chongc@...gle.com>; bondarn@...gle.com; linux-
> sgx@...r.kernel.org; dionnaglaze@...gle.com
> Subject: Re: [PATCH v6 2/5] x86/cpufeatures: Add
> X86_FEATURE_SGX_EUPDATESVN feature flag
> 
> On Thu, 2025-05-22 at 12:21 +0300, Elena Reshetova wrote:
> > --- a/tools/arch/x86/include/asm/cpufeatures.h
> > +++ b/tools/arch/x86/include/asm/cpufeatures.h
> > @@ -481,6 +481,7 @@
> >  #define X86_FEATURE_AMD_HTR_CORES	(21*32+ 6) /* Heterogeneous
> Core Topology */
> >  #define X86_FEATURE_AMD_WORKLOAD_CLASS	(21*32+ 7) /*
> Workload Classification */
> >  #define X86_FEATURE_PREFER_YMM		(21*32+ 8) /* Avoid ZMM
> registers due to downclocking */
> > +#define X86_FEATURE_SGX_EUPDATESVN	(21*32+11) /* Support for
> ENCLS[EUPDATESVN] instruction */
> 
> [Sorry for not mentioning in the previous version.]
> 
> Nit:
> 
> I am not sure we need to change tool headers.
> 
> Per commit
> 
>   f6d9883f8e68 ("tools/include: Sync x86 headers with the kernel sources")
> 
> .. and tools/include/uapi/README:
> 
>   ...
> 
>   What we are doing now is a third option:
> 
>    - A software-enforced copy-on-write mechanism of kernel headers to
>      tooling, driven by non-fatal warnings on the tooling side build when
>      kernel headers get modified:
> 
>       Warning: Kernel ABI header differences:
>         diff -u tools/include/uapi/drm/i915_drm.h include/uapi/drm/i915_drm.h
>         diff -u tools/include/uapi/linux/fs.h include/uapi/linux/fs.h
>         diff -u tools/include/uapi/linux/kvm.h include/uapi/linux/kvm.h
>         ...
> 
>      The tooling policy is to always pick up the kernel side headers as-is,
>      and integate them into the tooling build. The warnings above serve as a
>      notification to tooling maintainers that there's changes on the kernel
>      side.
> 
>   We've been using this for many years now, and it might seem hacky, but
>   works surprisingly well.
> 
> .. I interpret the updating to tools headers is not mandatory (unless building
> tools fails w/o the new feature bit definition which I believe isn't the case of
> SGX_UPDATESVN).  The tools maintainers will eventually do the sync.
> 
> But on the other hand, modifying tools headers in this patch also reduces
> tools
> maintainer's effort in the future.
> 
> That being said, I am unclear with the rule here.  Perhaps Dave/Ingo can help
> to
> clarify.


Thank you Kai! I am also not sure what is the rule since I have checked before
and different patches to x86/cpufeatures.c do it differently (some do the
updates to tools and some don't).
I also would like to hear suggestions from Dave and Ingo on this.

Best Regards,
Elena.