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[PATCH v5 00/12] x86/xsaves: Fix XSAVES issues

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  [PATCH v5 00/12] x86/xsaves: Fix XSAVES issues Yu-cheng Yu <yu-cheng.yu@intel.com> - 2016-05-09 23:00 +0200
    [PATCH v5 03/13] x86/xsaves: Keep init_fpstate.xsave.header.xfeatures as zero for init optimization Yu-cheng Yu <yu-cheng.yu@intel.com> - 2016-05-09 23:00 +0200

#1397399 — [PATCH v5 00/12] x86/xsaves: Fix XSAVES issues

XSAVES is a kernel-mode instruction. It offers a compacted format and
memory-write optimization. These patches fix issues in the first
implementation. They are intended for discussion and getting feedback
before actually getting applied.

Changes since Version 4:

Patch 4 - Introduce a new check to copy registers directly to signal
          frame: Simplify the check for compacted format.

Patch 7 - Fix PTRACE frames for XSAVES: If PTRACE attempts to set
          any disabled xstate, return failure; using_compacted_format()
          is used when appropriate.

New additions:

Patch 10 - Fix __fp_restore_sig() for xsaves: it was doing direct
           copying from user mode standard format to kernel mode,
           which could be in compacted format. Fix it by restoring
           directly to registers.

Patch 11 - Add WARN_ON_FPU() when a disabled xstate component is
           requested for a compacted format.

Patch 12 - Fix fpstate_init() for XSAVES: xcomp_bv[63] must be set
           for XSAVES.

Yu-cheng Yu (13):
  x86/xsaves: Define and use user_xstate_size for xstate size in signal
    context
  x86/xsaves: Rename xstate_size to kernel_xstate_size to explicitly
    distinguish xstate size in kernel from user space
  x86/xsaves: Keep init_fpstate.xsave.header.xfeatures as zero for init
    optimization
  x86/xsaves: Introduce a new check that allows correct xstates copy
    from kernel to user directly
  x86/xsaves: Align xstate components according to CPUID
  x86/xsaves: Supervisor state component offset
  x86/xsaves: Fix PTRACE frames for XSAVES
  x86/xsaves: Fix XSTATE component offset print out
  x86/xsaves: Fix xstate_offsets, xstate_sizes for non-extended states
  x86/xsaves: Fix __fpu_restore_sig() for XSAVES
  x86/xsaves: Add WARN_ON_FPU() when a disabled xstate component offset
    is requested for a compacted format
  x86/xsaves: Fix fpstate_init() for XSAVES
  x86/xsaves: Re-enable XSAVES

 arch/x86/include/asm/fpu/types.h  |   1 +
 arch/x86/include/asm/fpu/xstate.h |  10 +-
 arch/x86/include/asm/processor.h  |   3 +-
 arch/x86/kernel/fpu/core.c        |   9 +-
 arch/x86/kernel/fpu/init.c        |  32 +--
 arch/x86/kernel/fpu/regset.c      |  56 ++++--
 arch/x86/kernel/fpu/signal.c      |  42 +++-
 arch/x86/kernel/fpu/xstate.c      | 408 ++++++++++++++++++++++++++++++--------
 8 files changed, 420 insertions(+), 141 deletions(-)

-- 
1.9.1

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#1397400 — [PATCH v5 03/13] x86/xsaves: Keep init_fpstate.xsave.header.xfeatures as zero for init optimization

Keep init_fpstate.xsave.header.xfeatures as zero for init optimization.
This is important for init optimization that is implemented in processor.
If a bit corresponding to an xstate in xstate_bv is 0, it means the
xstate is in init status and will not be read from memory to the processor
during XRSTOR/XRSTORS instruction. This largely impacts context switch
performance.

Signed-off-by: Fenghua Yu <fenghua.yu@intel.com>
Signed-off-by: Yu-cheng Yu <yu-cheng.yu@intel.com>
Reviewed-by: Dave Hansen <dave.hansen@intel.com>
---
 arch/x86/kernel/fpu/xstate.c | 6 ++----
 1 file changed, 2 insertions(+), 4 deletions(-)

diff --git a/arch/x86/kernel/fpu/xstate.c b/arch/x86/kernel/fpu/xstate.c
index 20c6631..170c164 100644
--- a/arch/x86/kernel/fpu/xstate.c
+++ b/arch/x86/kernel/fpu/xstate.c
@@ -324,13 +324,11 @@ static void __init setup_init_fpu_buf(void)
 	setup_xstate_features();
 	print_xstate_features();
 
-	if (cpu_has_xsaves) {
+	if (cpu_has_xsaves)
 		init_fpstate.xsave.header.xcomp_bv = (u64)1 << 63 | xfeatures_mask;
-		init_fpstate.xsave.header.xfeatures = xfeatures_mask;
-	}
 
 	/*
-	 * Init all the features state with header_bv being 0x0
+	 * Init all the features state with header.xfeatures being 0x0
 	 */
 	copy_kernel_to_xregs_booting(&init_fpstate.xsave);
 
-- 
1.9.1

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