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From: Borislav Petkov <bp@alien8.de>
To: "Kuppuswamy,
	Sathyanarayanan"  <sathyanarayanan.kuppuswamy@linux.intel.com>
Cc: Thomas Gleixner <tglx@linutronix.de>,
	Ingo Molnar <mingo@redhat.com>,
	x86@kernel.org, Paolo Bonzini <pbonzini@redhat.com>,
	David Hildenbrand <david@redhat.com>,
	Andrea Arcangeli <aarcange@redhat.com>,
	Josh Poimboeuf <jpoimboe@redhat.com>,
	Juergen Gross <jgross@suse.com>, Deep Shah <sdeep@vmware.com>,
	VMware Inc <pv-drivers@vmware.com>,
	Vitaly Kuznetsov <vkuznets@redhat.com>,
	Wanpeng Li <wanpengli@tencent.com>,
	Jim Mattson <jmattson@google.com>, Joerg Roedel <joro@8bytes.org>,
	Peter H Anvin <hpa@zytor.com>,
	Dave Hansen <dave.hansen@intel.com>,
	Tony Luck <tony.luck@intel.com>,
	Dan Williams <dan.j.williams@intel.com>,
	Andi Kleen <ak@linux.intel.com>,
	Kirill Shutemov <kirill.shutemov@linux.intel.com>,
	Sean Christopherson <seanjc@google.com>,
	Kuppuswamy Sathyanarayanan <knsathya@kernel.org>,
	linux-kernel@vger.kernel.org
Subject: Re: [PATCH v8 03/11] x86/cpufeatures: Add TDX Guest CPU feature
Date: Wed, 6 Oct 2021 18:20:41 +0200	[thread overview]
Message-ID: <YV3M2cqqMTkC/rUK@zn.tnic> (raw)
In-Reply-To: <328cc0e7-89e7-a1b2-f798-fe758c2c1f4e@linux.intel.com>

On Wed, Oct 06, 2021 at 08:43:48AM -0700, Kuppuswamy, Sathyanarayanan wrote:
> Yes. But, Joerg Roedel in his review recommended using variable
> similar to sme_me_mask to avoid function call in Intel platform in
> cc_platform_has().

That would normally make sense if this were a fast path. But I don't see
that being one. Besides, the subsequent runs will be the function call +
a couple of instructions:

# arch/x86/kernel/tdx.c:22: 	if (tdx_guest >= 0)
	movl	tdx_guest(%rip), %eax	# tdx_guest,
	testl	%eax, %eax	#
	jns	.L11	#,

...

.L11:
# arch/x86/kernel/tdx.c:23: 		return tdx_guest;
	setne	%al	#, <retval>
# arch/x86/kernel/tdx.c:35: }
	ret

which is not the end of the world.

And it if it is really used in a fast path, then we can do a static
branch etc.

Thx.

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette

  reply	other threads:[~2021-10-06 16:20 UTC|newest]

Thread overview: 77+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-10-05  2:51 [PATCH v8 00/11] Add TDX Guest Support (Initial support) Kuppuswamy Sathyanarayanan
2021-10-05  2:51 ` [PATCH v8 01/11] x86/paravirt: Move halt paravirt calls under CONFIG_PARAVIRT Kuppuswamy Sathyanarayanan
2021-10-05 20:13   ` Josh Poimboeuf
2021-10-05  2:51 ` [PATCH v8 02/11] x86/tdx: Introduce INTEL_TDX_GUEST config option Kuppuswamy Sathyanarayanan
2021-10-05  4:53   ` Randy Dunlap
2021-10-05 13:29     ` Sathyanarayanan Kuppuswamy Natarajan
2021-10-05 14:09       ` Dave Hansen
2021-10-05 14:31         ` Sean Christopherson
2021-10-05 14:43         ` Kuppuswamy, Sathyanarayanan
2021-10-05 14:13       ` Borislav Petkov
2021-10-05 14:48         ` Kuppuswamy, Sathyanarayanan
2021-10-05 17:29           ` Borislav Petkov
2021-10-05 20:21             ` Josh Poimboeuf
2021-10-05 20:38               ` Kuppuswamy, Sathyanarayanan
2021-10-05 20:17   ` Josh Poimboeuf
2021-10-05 20:33     ` Sean Christopherson
2021-10-05 20:42       ` Dave Hansen
2021-10-05 20:37     ` Kuppuswamy, Sathyanarayanan
2021-10-05  2:51 ` [PATCH v8 03/11] x86/cpufeatures: Add TDX Guest CPU feature Kuppuswamy Sathyanarayanan
2021-10-05 21:04   ` Josh Poimboeuf
2021-10-05 21:19     ` Borislav Petkov
2021-10-05 21:41     ` Kuppuswamy, Sathyanarayanan
2021-10-06  3:42       ` Josh Poimboeuf
2021-10-06  4:33         ` Kuppuswamy, Sathyanarayanan
2021-10-06  5:03           ` Josh Poimboeuf
2021-10-06 12:47             ` Borislav Petkov
2021-10-06 14:11               ` Josh Poimboeuf
2021-10-06 14:26                 ` Borislav Petkov
2021-10-06 14:25   ` Josh Poimboeuf
2021-10-06 15:26   ` Borislav Petkov
2021-10-06 15:43     ` Kuppuswamy, Sathyanarayanan
2021-10-06 16:20       ` Borislav Petkov [this message]
2021-10-05  2:51 ` [PATCH v8 04/11] x86/tdx: Add Intel ARCH support to cc_platform_has() Kuppuswamy Sathyanarayanan
2021-10-05  4:47   ` Randy Dunlap
2021-10-05 12:29     ` Kuppuswamy, Sathyanarayanan
2021-10-05 21:16   ` Josh Poimboeuf
2021-10-05 21:42     ` Kuppuswamy, Sathyanarayanan
2021-10-06 18:02     ` Borislav Petkov
2021-10-06 18:14       ` Kuppuswamy, Sathyanarayanan
2021-10-05  2:51 ` [PATCH v8 05/11] x86/tdx: Add __tdx_module_call() and __tdx_hypercall() helper functions Kuppuswamy Sathyanarayanan
2021-10-06  5:53   ` Josh Poimboeuf
2021-10-06 16:52     ` Kuppuswamy, Sathyanarayanan
2021-10-07  9:33   ` Borislav Petkov
2021-10-07 16:55     ` Kuppuswamy, Sathyanarayanan
2021-10-05  2:52 ` [PATCH v8 06/11] x86/traps: Add #VE support for TDX guest Kuppuswamy Sathyanarayanan
2021-10-06 18:40   ` Josh Poimboeuf
2021-10-07 17:06   ` Borislav Petkov
2021-10-07 17:22     ` Kuppuswamy, Sathyanarayanan
2021-10-07 17:32       ` Borislav Petkov
2021-10-17 17:15     ` Dave Hansen
2021-10-18 10:53       ` Borislav Petkov
2021-10-18 14:05         ` Dave Hansen
2021-10-18 14:09           ` Borislav Petkov
2021-10-09  3:56   ` Lai Jiangshan
2021-10-11 15:06     ` Sean Christopherson
2021-10-11 16:49       ` Andi Kleen
2021-10-05  2:52 ` [PATCH v8 07/11] x86/tdx: Add HLT " Kuppuswamy Sathyanarayanan
2021-10-06 19:17   ` Josh Poimboeuf
2021-10-07 19:25     ` Kuppuswamy, Sathyanarayanan
2021-10-08 17:31   ` Borislav Petkov
2021-10-08 17:38     ` Kuppuswamy, Sathyanarayanan
2021-10-08 17:59       ` Borislav Petkov
2021-10-05  2:52 ` [PATCH v8 08/11] x86/tdx: Wire up KVM hypercalls Kuppuswamy Sathyanarayanan
2021-10-06 19:34   ` Josh Poimboeuf
2021-10-06 19:40     ` Borislav Petkov
2021-11-05 20:59   ` Sean Christopherson
2021-11-12 16:17     ` Sathyanarayanan Kuppuswamy
2021-10-05  2:52 ` [PATCH v8 09/11] x86/tdx: Add MSR support for TDX guest Kuppuswamy Sathyanarayanan
2021-10-05 23:22   ` Josh Poimboeuf
2021-10-06  0:48     ` Kuppuswamy, Sathyanarayanan
2021-10-06 19:49   ` Josh Poimboeuf
2021-10-08  2:16     ` Kuppuswamy, Sathyanarayanan
2021-10-05  2:52 ` [PATCH v8 10/11] x86/tdx: Don't write CSTAR MSR on Intel Kuppuswamy Sathyanarayanan
2021-10-05  2:52 ` [PATCH v8 11/11] x86/tdx: Handle CPUID via #VE Kuppuswamy Sathyanarayanan
2021-10-06 20:26   ` Josh Poimboeuf
2021-10-08  2:25     ` Kuppuswamy, Sathyanarayanan
2021-10-11 18:16       ` Josh Poimboeuf

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