Groups | Search | Server Info | Keyboard shortcuts | Login | Register [http] [https] [nntp] [nntps]

Groups > linux.kernel > #1321982

[PATCH 02/31] x86, fpu: add placeholder for Processor Trace XSAVE state

Show all headers | View raw

From: Dave Hansen <dave.hansen@linux.intel.com>

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 <dave.hansen@linux.intel.com>
Reviewed-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Andi Kleen <ak@linux.intel.com>
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	2016-01-28 15:52:17.216259779 -0800
+++ b/arch/x86/include/asm/fpu/types.h	2016-01-28 15:52:17.220259963 -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	2016-01-28 15:52:17.217259825 -0800
+++ b/arch/x86/kernel/fpu/xstate.c	2016-01-28 15:52:17.221260009 -0800
@@ -13,6 +13,11 @@
 
 #include <asm/tlbflush.h>
 
+/*
+ * 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);
 	}
_

Back to linux.kernel | Previous | Next — Previous in thread | Next in thread | Find similar | Unroll thread

Thread

[PATCH 00/31] x86: Memory Protection Keys (v9) Dave Hansen <dave@sr71.net> - 2016-01-29 19:20 +0100
  [PATCH 21/31] x86, pkeys: dump PKRU with other kernel registers Dave Hansen <dave@sr71.net> - 2016-01-29 19:20 +0100
  [PATCH 26/31] x86, pkeys: add arch_validate_pkey() Dave Hansen <dave@sr71.net> - 2016-01-29 19:20 +0100
  [PATCH 29/31] x86, pkeys: allow kernel to modify user pkey rights register Dave Hansen <dave@sr71.net> - 2016-01-29 19:20 +0100
  [PATCH 03/31] x86, pkeys: Add Kconfig option Dave Hansen <dave@sr71.net> - 2016-01-29 19:20 +0100
  [PATCH 09/31] x86, pkeys: store protection in high VMA flags Dave Hansen <dave@sr71.net> - 2016-01-29 19:20 +0100
  [PATCH 05/31] x86, pkeys: define new CR4 bit Dave Hansen <dave@sr71.net> - 2016-01-29 19:30 +0100
  [PATCH 23/31] x86, pkeys: add Kconfig prompt to existing config option Dave Hansen <dave@sr71.net> - 2016-01-29 19:30 +0100
  [PATCH 12/31] signals, pkeys: notify userspace about protection key faults Dave Hansen <dave@sr71.net> - 2016-01-29 19:30 +0100
  [PATCH 24/31] x86, pkeys: actually enable Memory Protection Keys in CPU Dave Hansen <dave@sr71.net> - 2016-01-29 19:30 +0100
  [PATCH 15/31] mm: factor out VMA fault permission checking Dave Hansen <dave@sr71.net> - 2016-01-29 19:30 +0100
  [PATCH 20/31] x86, pkeys: differentiate instruction fetches Dave Hansen <dave@sr71.net> - 2016-01-29 19:30 +0100
  [PATCH 18/31] mm: do not enforce PKEY permissions on "foreign" mm access Dave Hansen <dave@sr71.net> - 2016-01-29 19:30 +0100
  [PATCH 08/31] x86, pkeys: new page fault error code bit: PF_PK Dave Hansen <dave@sr71.net> - 2016-01-29 19:30 +0100
  [PATCH 14/31] x86, pkeys: add functions to fetch PKRU Dave Hansen <dave@sr71.net> - 2016-01-29 19:30 +0100
  [PATCH 04/31] x86, pkeys: cpuid bit definition Dave Hansen <dave@sr71.net> - 2016-01-29 19:30 +0100
  [PATCH 10/31] x86, pkeys: arch-specific protection bits Dave Hansen <dave@sr71.net> - 2016-01-29 19:30 +0100
  [PATCH 13/31] x86, pkeys: fill in pkey field in siginfo Dave Hansen <dave@sr71.net> - 2016-01-29 19:30 +0100
  [PATCH 25/31] mm, multi-arch: pass a protection key in to calc_vm_flag_bits() Dave Hansen <dave@sr71.net> - 2016-01-29 19:30 +0100
  [PATCH 17/31] x86, pkeys: check VMAs and PTEs for protection keys Dave Hansen <dave@sr71.net> - 2016-01-29 19:30 +0100
  [PATCH 07/31] x86, pkeys: PTE bits for storing protection key Dave Hansen <dave@sr71.net> - 2016-01-29 19:30 +0100
  [PATCH 02/31] x86, fpu: add placeholder for Processor Trace XSAVE state Dave Hansen <dave@sr71.net> - 2016-01-29 19:30 +0100
  [PATCH 16/31] x86, mm: simplify get_user_pages() PTE bit handling Dave Hansen <dave@sr71.net> - 2016-01-29 19:30 +0100
  [PATCH 11/31] x86, pkeys: pass VMA down in to fault signal generation code Dave Hansen <dave@sr71.net> - 2016-01-29 19:30 +0100
  [PATCH 22/31] x86, pkeys: dump pkey from VMA in /proc/pid/smaps Dave Hansen <dave@sr71.net> - 2016-01-29 19:30 +0100
    Re: [PATCH 22/31] x86, pkeys: dump pkey from VMA in /proc/pid/smaps Vlastimil Babka <vbabka@suse.cz> - 2016-02-02 17:20 +0100
      Re: [PATCH 22/31] x86, pkeys: dump pkey from VMA in /proc/pid/smaps Dave Hansen <dave@sr71.net> - 2016-02-02 20:10 +0100
  [PATCH 06/31] x86, pkeys: add PKRU xsave fields and data structure(s) Dave Hansen <dave@sr71.net> - 2016-01-29 19:30 +0100

csiph-web