From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pa0-f47.google.com (mail-pa0-f47.google.com [209.85.220.47]) by kanga.kvack.org (Postfix) with ESMTP id 72858828E4 for ; Fri, 12 Feb 2016 16:02:04 -0500 (EST) Received: by mail-pa0-f47.google.com with SMTP id ho8so52461723pac.2 for ; Fri, 12 Feb 2016 13:02:04 -0800 (PST) Received: from mga14.intel.com (mga14.intel.com. [192.55.52.115]) by mx.google.com with ESMTP id 22si17645213pfq.57.2016.02.12.13.01.59 for ; Fri, 12 Feb 2016 13:01:59 -0800 (PST) Subject: [PATCH 04/33] x86, fpu: add placeholder for Processor Trace XSAVE state From: Dave Hansen Date: Fri, 12 Feb 2016 13:01:58 -0800 References: <20160212210152.9CAD15B0@viggo.jf.intel.com> In-Reply-To: <20160212210152.9CAD15B0@viggo.jf.intel.com> Message-Id: <20160212210158.5E4BCAE2@viggo.jf.intel.com> Sender: owner-linux-mm@kvack.org List-ID: To: linux-kernel@vger.kernel.org Cc: linux-mm@kvack.org, x86@kernel.org, torvalds@linux-foundation.org, Dave Hansen , dave.hansen@linux.intel.com, ak@linux.intel.com, yu-cheng.yu@intel.com, fenghua.yu@intel.com From: Dave Hansen There is an XSAVE state component for Intel Processor Trace (PT). But, we do not currently use it. We add a placeholder in the code for it so it is not a mystery and also so we do not need an explicit enum initialization for Protection Keys in a moment. Why don't we use it? We might end up using this at _some_ point in the future. But, this is a "system" state which requires using the currently unsupported XSAVES feature. Unlike all the other XSAVE states, PT state is also not directly tied to a thread. You might context-switch between threads, but not want to change any of the PT state. Or, you might switch between threads, and *do* want to change PT state, all depending on what is being traced. We currently just manually set some MSRs to do this PT context switching, and it is unclear whether replacing our direct MSR use with XSAVE will be a net win or loss, both in code complexity and performance. Signed-off-by: Dave Hansen Reviewed-by: Thomas Gleixner Cc: Andi Kleen Cc: yu-cheng.yu@intel.com Cc: fenghua.yu@intel.com --- b/arch/x86/include/asm/fpu/types.h | 1 + b/arch/x86/kernel/fpu/xstate.c | 10 ++++++++-- 2 files changed, 9 insertions(+), 2 deletions(-) diff -puN arch/x86/include/asm/fpu/types.h~pt-xstate-bit arch/x86/include/asm/fpu/types.h --- a/arch/x86/include/asm/fpu/types.h~pt-xstate-bit 2016-02-12 10:44:15.475212032 -0800 +++ b/arch/x86/include/asm/fpu/types.h 2016-02-12 10:44:15.479212215 -0800 @@ -108,6 +108,7 @@ enum xfeature { XFEATURE_OPMASK, XFEATURE_ZMM_Hi256, XFEATURE_Hi16_ZMM, + XFEATURE_PT_UNIMPLEMENTED_SO_FAR, XFEATURE_MAX, }; diff -puN arch/x86/kernel/fpu/xstate.c~pt-xstate-bit arch/x86/kernel/fpu/xstate.c --- a/arch/x86/kernel/fpu/xstate.c~pt-xstate-bit 2016-02-12 10:44:15.476212078 -0800 +++ b/arch/x86/kernel/fpu/xstate.c 2016-02-12 10:44:15.480212261 -0800 @@ -13,6 +13,11 @@ #include +/* + * Although we spell it out in here, the Processor Trace + * xfeature is completely unused. We use other mechanisms + * to save/restore PT state in Linux. + */ static const char *xfeature_names[] = { "x87 floating point registers" , @@ -23,7 +28,7 @@ static const char *xfeature_names[] = "AVX-512 opmask" , "AVX-512 Hi256" , "AVX-512 ZMM_Hi256" , - "unknown xstate feature" , + "Processor Trace (unused)" , }; /* @@ -470,7 +475,8 @@ static void check_xstate_against_struct( * numbers. */ if ((nr < XFEATURE_YMM) || - (nr >= XFEATURE_MAX)) { + (nr >= XFEATURE_MAX) || + (nr == XFEATURE_PT_UNIMPLEMENTED_SO_FAR)) { WARN_ONCE(1, "no structure for xstate: %d\n", nr); XSTATE_WARN_ON(1); } _ -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org