[patch 0/3] x86: xsaveopt kernel enabling patches

[patch 0/3] x86: xsaveopt kernel enabling patches

[Suresh Siddha]

AVX Programming Reference (June, 2010 version) located at
http://software.intel.com/en-us/avx/ refers to the optimized
extended state save instruction "xsaveopt".

xsaveopt is similar to xsave and incorporates optimizations specifically
targeted for speeding up context switch save, like:
a. if a state is in an INIT state, the instruction may clear the corresponding
   bit in the xheader.bv with out writing the actual state in to the memory.
b. if the state hasn't been modified since the last xrstor, the instruction
   may not write out the state to the save area.

Following patches enable the use of xsaveopt for context switch save/restore
of the extended state.

Signed-off-by: Suresh Siddha <suresh.b.siddha@intel.com>

[patch 1/3] x86: track the offset, size of features state in the xsave layout

[Suresh Siddha]

[-- Attachment #1: xstate_feature_offset_size.patch --]
[-- Type: text/plain, Size: 1652 bytes --]

Subleaves of the cpuid vector 0xd provides the offset and size of different
feature state that are managed by the xsave/xrstor. Track this for the upcoming
usage during signal handling.

Signed-off-by: Suresh Siddha <suresh.b.siddha@intel.com>
---
 arch/x86/kernel/xsave.c |   29 +++++++++++++++++++++++++++++
 1 file changed, 29 insertions(+)

Index: tip/arch/x86/kernel/xsave.c
===================================================================
--- tip.orig/arch/x86/kernel/xsave.c
+++ tip/arch/x86/kernel/xsave.c
@@ -21,6 +21,8 @@ struct _fpx_sw_bytes fx_sw_reserved;
 struct _fpx_sw_bytes fx_sw_reserved_ia32;
 #endif
 
+static unsigned int *xstate_offsets, *xstate_sizes, xstate_features;
+
 /*
  * Check for the presence of extended state information in the
  * user fpstate pointer in the sigcontext.
@@ -294,12 +296,39 @@ void __cpuinit xsave_init(void)
 }
 
 /*
+ * Record the offsets and sizes of different state managed by the xsave
+ * memory layout.
+ */
+static void setup_xstate_features(void)
+{
+	int eax, ebx, ecx, edx, leaf = 0x2;
+
+	xstate_features = fls64(pcntxt_mask);
+	xstate_offsets = alloc_bootmem(xstate_features * sizeof(int));
+	xstate_sizes = alloc_bootmem(xstate_features * sizeof(int));
+
+	do {
+		cpuid_count(0xd, leaf, &eax, &ebx, &ecx, &edx);
+
+		if (eax == 0)
+			break;
+
+		xstate_offsets[leaf] = ebx;
+		xstate_sizes[leaf] = eax;
+
+		leaf++;
+	} while (1);
+}
+
+/*
  * setup the xstate image representing the init state
  */
 static void __init setup_xstate_init(void)
 {
 	init_xstate_buf = alloc_bootmem(xstate_size);
 	init_xstate_buf->i387.mxcsr = MXCSR_DEFAULT;
+
+	setup_xstate_features();
 }
 
 /*

[patch 2/3] x86: sync xsave memory layout with its header for user handling

[Suresh Siddha]

[-- Attachment #1: fix_signal_handling_with_xsaveopt_init_optimization.patch --]
[-- Type: text/plain, Size: 6988 bytes --]

With xsaveopt, if a processor implementation discern that a processor state
component is in its initialized state it may modify the corresponding bit in
the xsave_hdr.xstate_bv as '0', with out modifying the corresponding memory
layout. Hence wHile presenting the xstate information to the user, we always
ensure that the memory layout of a feature will be in the init state if the
corresponding header bit is zero. This ensures the consistency and avoids the
condition of the user seeing some some stale state in the memory layout during
signal handling, debugging etc.

Signed-off-by: Suresh Siddha <suresh.b.siddha@intel.com>
---
 arch/x86/include/asm/i387.h  |   14 ++++++
 arch/x86/include/asm/xsave.h |   10 ++++
 arch/x86/kernel/i387.c       |   11 +++++
 arch/x86/kernel/xsave.c      |   89 ++++++++++++++++++++++++++++++++++++++++++-
 4 files changed, 123 insertions(+), 1 deletion(-)

Index: tip-linux-2.6/arch/x86/kernel/xsave.c
===================================================================
--- tip-linux-2.6.orig/arch/x86/kernel/xsave.c
+++ tip-linux-2.6/arch/x86/kernel/xsave.c
@@ -24,6 +24,76 @@ struct _fpx_sw_bytes fx_sw_reserved_ia32
 static unsigned int *xstate_offsets, *xstate_sizes, xstate_features;
 
 /*
+ * If a processor implementation discern that a processor state component is
+ * in its initialized state it may modify the corresponding bit in the
+ * xsave_hdr.xstate_bv as '0', with out modifying the corresponding memory
+ * layout in the case of xsaveopt. While presenting the xstate information to
+ * the user, we always ensure that the memory layout of a feature will be in
+ * the init state if the corresponding header bit is zero. This is to ensure
+ * that the user doesn't see some stale state in the memory layout during
+ * signal handling, debugging etc.
+ */
+void __sanitize_i387_state(struct task_struct *tsk)
+{
+	u64 xstate_bv;
+	int feature_bit = 0x2;
+	struct i387_fxsave_struct *fx = &tsk->thread.fpu.state->fxsave;
+
+	if (!fx)
+		return;
+
+	BUG_ON(task_thread_info(tsk)->status & TS_USEDFPU);
+
+	xstate_bv = tsk->thread.fpu.state->xsave.xsave_hdr.xstate_bv;
+
+	/*
+	 * None of the feature bits are in init state. So nothing else
+	 * to do for us, as the memory layout is upto date.
+	 */
+	if ((xstate_bv & pcntxt_mask) == pcntxt_mask)
+		return;
+
+	/*
+	 * FP is in init state
+	 */
+	if (!(xstate_bv & XSTATE_FP)) {
+		fx->cwd = 0x37f;
+		fx->swd = 0;
+		fx->twd = 0;
+		fx->fop = 0;
+		fx->rip = 0;
+		fx->rdp = 0;
+		memset(&fx->st_space[0], 0, 128);
+	}
+
+	/*
+	 * SSE is in init state
+	 */
+	if (!(xstate_bv & XSTATE_SSE))
+		memset(&fx->xmm_space[0], 0, 256);
+
+	xstate_bv = (pcntxt_mask & ~xstate_bv) >> 2;
+
+	/*
+	 * Update all the other memory layouts for which the corresponding
+	 * header bit is in the init state.
+	 */
+	while (xstate_bv) {
+		if (xstate_bv & 0x1) {
+			int offset = xstate_offsets[feature_bit];
+			int size = xstate_sizes[feature_bit];
+
+			memcpy(((void *) fx) + offset,
+			       ((void *) init_xstate_buf) + offset,
+			       size);
+		}
+
+		xstate_bv >>= 1;
+		feature_bit++;
+	}
+}
+
+/*
  * Check for the presence of extended state information in the
  * user fpstate pointer in the sigcontext.
  */
@@ -104,6 +174,7 @@ int save_i387_xstate(void __user *buf)
 		task_thread_info(tsk)->status &= ~TS_USEDFPU;
 		stts();
 	} else {
+		sanitize_i387_state(tsk);
 		if (__copy_to_user(buf, &tsk->thread.fpu.state->fxsave,
 				   xstate_size))
 			return -1;
@@ -325,10 +396,26 @@ static void setup_xstate_features(void)
  */
 static void __init setup_xstate_init(void)
 {
+	setup_xstate_features();
+
+	/*
+	 * Setup init_xstate_buf to represent the init state of
+	 * all the features managed by the xsave
+	 */
 	init_xstate_buf = alloc_bootmem(xstate_size);
 	init_xstate_buf->i387.mxcsr = MXCSR_DEFAULT;
 
-	setup_xstate_features();
+	clts();
+	/*
+	 * Init all the features state with header_bv being 0x0
+	 */
+	xrstor_state(init_xstate_buf, -1);
+	/*
+	 * Dump the init state again. This is to identify the init state
+	 * of any feature which is not represented by all zero's.
+	 */
+	xsave_state(init_xstate_buf, -1);
+	stts();
 }
 
 /*
Index: tip-linux-2.6/arch/x86/kernel/i387.c
===================================================================
--- tip-linux-2.6.orig/arch/x86/kernel/i387.c
+++ tip-linux-2.6/arch/x86/kernel/i387.c
@@ -190,6 +190,8 @@ int xfpregs_get(struct task_struct *targ
 	if (ret)
 		return ret;
 
+	sanitize_i387_state(target);
+
 	return user_regset_copyout(&pos, &count, &kbuf, &ubuf,
 				   &target->thread.fpu.state->fxsave, 0, -1);
 }
@@ -207,6 +209,8 @@ int xfpregs_set(struct task_struct *targ
 	if (ret)
 		return ret;
 
+	sanitize_i387_state(target);
+
 	ret = user_regset_copyin(&pos, &count, &kbuf, &ubuf,
 				 &target->thread.fpu.state->fxsave, 0, -1);
 
@@ -446,6 +450,8 @@ int fpregs_get(struct task_struct *targe
 					   -1);
 	}
 
+	sanitize_i387_state(target);
+
 	if (kbuf && pos == 0 && count == sizeof(env)) {
 		convert_from_fxsr(kbuf, target);
 		return 0;
@@ -467,6 +473,8 @@ int fpregs_set(struct task_struct *targe
 	if (ret)
 		return ret;
 
+	sanitize_i387_state(target);
+
 	if (!HAVE_HWFP)
 		return fpregs_soft_set(target, regset, pos, count, kbuf, ubuf);
 
@@ -533,6 +541,9 @@ static int save_i387_xsave(void __user *
 	struct _fpstate_ia32 __user *fx = buf;
 	int err = 0;
 
+
+	sanitize_i387_state(tsk);
+
 	/*
 	 * For legacy compatible, we always set FP/SSE bits in the bit
 	 * vector while saving the state to the user context.
Index: tip-linux-2.6/arch/x86/include/asm/i387.h
===================================================================
--- tip-linux-2.6.orig/arch/x86/include/asm/i387.h
+++ tip-linux-2.6/arch/x86/include/asm/i387.h
@@ -58,11 +58,25 @@ extern int restore_i387_xstate_ia32(void
 
 #define X87_FSW_ES (1 << 7)	/* Exception Summary */
 
+static __always_inline __pure bool use_xsaveopt(void)
+{
+	return 0;
+}
+
 static __always_inline __pure bool use_xsave(void)
 {
 	return static_cpu_has(X86_FEATURE_XSAVE);
 }
 
+extern void __sanitize_i387_state(struct task_struct *);
+
+static inline void sanitize_i387_state(struct task_struct *tsk)
+{
+	if (!use_xsaveopt())
+		return;
+	__sanitize_i387_state(tsk);
+}
+
 #ifdef CONFIG_X86_64
 
 /* Ignore delayed exceptions from user space */
Index: tip-linux-2.6/arch/x86/include/asm/xsave.h
===================================================================
--- tip-linux-2.6.orig/arch/x86/include/asm/xsave.h
+++ tip-linux-2.6/arch/x86/include/asm/xsave.h
@@ -121,6 +121,16 @@ static inline void xrstor_state(struct x
 		     :   "memory");
 }
 
+static inline void xsave_state(struct xsave_struct *fx, u64 mask)
+{
+	u32 lmask = mask;
+	u32 hmask = mask >> 32;
+
+	asm volatile(".byte " REX_PREFIX "0x0f,0xae,0x27\n\t"
+		     : : "D" (fx), "m" (*fx), "a" (lmask), "d" (hmask)
+		     :   "memory");
+}
+
 static inline void fpu_xsave(struct fpu *fpu)
 {
 	/* This, however, we can work around by forcing the compiler to select

[patch 3/3] x86: use xsaveopt in context-switch path when supported

[Suresh Siddha]

[-- Attachment #1: xsaveopt_support.patch --]
[-- Type: text/plain, Size: 5151 bytes --]

xsaveopt is a more optimized form of xsave specifically designed
for the context switch usage. xsaveopt doesn't save the state that's not
modified from the prior xrstor. And if a specific feature state gets
modified to the init state, then xsaveopt just updates the header bit
in the xsave memory layout without updating the corresponding memory
layout.

Signed-off-by: Suresh Siddha <suresh.b.siddha@intel.com>
---
 arch/x86/include/asm/cpufeature.h          |    1 +
 arch/x86/include/asm/i387.h                |    2 +-
 arch/x86/include/asm/xsave.h               |    9 ++++++---
 arch/x86/kernel/cpu/addon_cpuid_features.c |   24 +++++++++++++-----------
 arch/x86/kernel/cpu/common.c               |    8 ++++++++
 5 files changed, 29 insertions(+), 15 deletions(-)

Index: tip/arch/x86/kernel/cpu/addon_cpuid_features.c
===================================================================
--- tip.orig/arch/x86/kernel/cpu/addon_cpuid_features.c
+++ tip/arch/x86/kernel/cpu/addon_cpuid_features.c
@@ -13,6 +13,7 @@ struct cpuid_bit {
 	u16 feature;
 	u8 reg;
 	u8 bit;
+	u32 leaf;
 	u32 level;
 };
 
@@ -30,15 +31,16 @@ void __cpuinit init_scattered_cpuid_feat
 	const struct cpuid_bit *cb;
 
 	static const struct cpuid_bit __cpuinitconst cpuid_bits[] = {
-		{ X86_FEATURE_IDA,   		CR_EAX, 1, 0x00000006 },
-		{ X86_FEATURE_ARAT,  		CR_EAX, 2, 0x00000006 },
-		{ X86_FEATURE_APERFMPERF,	CR_ECX, 0, 0x00000006 },
-		{ X86_FEATURE_EPB,		CR_ECX, 3, 0x00000006 },
-		{ X86_FEATURE_CPB,   		CR_EDX, 9, 0x80000007 },
-		{ X86_FEATURE_NPT,   		CR_EDX, 0, 0x8000000a },
-		{ X86_FEATURE_LBRV,  		CR_EDX, 1, 0x8000000a },
-		{ X86_FEATURE_SVML,  		CR_EDX, 2, 0x8000000a },
-		{ X86_FEATURE_NRIPS, 		CR_EDX, 3, 0x8000000a },
+		{ X86_FEATURE_IDA,		CR_EAX, 1, 0, 0x00000006 },
+		{ X86_FEATURE_ARAT,		CR_EAX, 2, 0, 0x00000006 },
+		{ X86_FEATURE_APERFMPERF,	CR_ECX, 0, 0, 0x00000006 },
+		{ X86_FEATURE_EPB,		CR_ECX, 3, 0, 0x00000006 },
+		{ X86_FEATURE_CPB,		CR_EDX, 9, 0, 0x80000007 },
+		{ X86_FEATURE_NPT,		CR_EDX, 0, 0, 0x8000000a },
+		{ X86_FEATURE_LBRV,		CR_EDX, 1, 0, 0x8000000a },
+		{ X86_FEATURE_SVML,		CR_EDX, 2, 0, 0x8000000a },
+		{ X86_FEATURE_NRIPS,		CR_EDX, 3, 0, 0x8000000a },
+		{ X86_FEATURE_XSAVEOPT,		CR_EAX, 0, 1, 0x0000000d },
 		{ 0, 0, 0, 0 }
 	};
 
@@ -50,8 +52,8 @@ void __cpuinit init_scattered_cpuid_feat
 		    max_level > (cb->level | 0xffff))
 			continue;
 
-		cpuid(cb->level, &regs[CR_EAX], &regs[CR_EBX],
-			&regs[CR_ECX], &regs[CR_EDX]);
+		cpuid_count(cb->level, cb->leaf, &regs[CR_EAX], &regs[CR_EBX],
+			    &regs[CR_ECX], &regs[CR_EDX]);
 
 		if (regs[cb->reg] & (1 << cb->bit))
 			set_cpu_cap(c, cb->feature);
Index: tip/arch/x86/include/asm/cpufeature.h
===================================================================
--- tip.orig/arch/x86/include/asm/cpufeature.h
+++ tip/arch/x86/include/asm/cpufeature.h
@@ -165,6 +165,7 @@
 #define X86_FEATURE_ARAT	(7*32+ 1) /* Always Running APIC Timer */
 #define X86_FEATURE_CPB		(7*32+ 2) /* AMD Core Performance Boost */
 #define X86_FEATURE_EPB		(7*32+ 3) /* IA32_ENERGY_PERF_BIAS support */
+#define X86_FEATURE_XSAVEOPT	(7*32+4) /* "xsaveopt" Optimized Xsave */
 
 /* Virtualization flags: Linux defined, word 8 */
 #define X86_FEATURE_TPR_SHADOW  (8*32+ 0) /* Intel TPR Shadow */
Index: tip/arch/x86/include/asm/xsave.h
===================================================================
--- tip.orig/arch/x86/include/asm/xsave.h
+++ tip/arch/x86/include/asm/xsave.h
@@ -135,8 +135,11 @@ static inline void fpu_xsave(struct fpu 
 {
 	/* This, however, we can work around by forcing the compiler to select
 	   an addressing mode that doesn't require extended registers. */
-	__asm__ __volatile__(".byte " REX_PREFIX "0x0f,0xae,0x27"
-			     : : "D" (&(fpu->state->xsave)),
-				 "a" (-1), "d"(-1) : "memory");
+	alternative_input(
+		".byte " REX_PREFIX "0x0f,0xae,0x27",
+		".byte " REX_PREFIX "0x0f,0xae,0x37",
+		X86_FEATURE_XSAVEOPT,
+		[fx] "D" (&fpu->state->xsave), "a" (-1), "d" (-1) :
+		"memory");
 }
 #endif
Index: tip/arch/x86/kernel/cpu/common.c
===================================================================
--- tip.orig/arch/x86/kernel/cpu/common.c
+++ tip/arch/x86/kernel/cpu/common.c
@@ -140,10 +140,18 @@ EXPORT_PER_CPU_SYMBOL_GPL(gdt_page);
 static int __init x86_xsave_setup(char *s)
 {
 	setup_clear_cpu_cap(X86_FEATURE_XSAVE);
+	setup_clear_cpu_cap(X86_FEATURE_XSAVEOPT);
 	return 1;
 }
 __setup("noxsave", x86_xsave_setup);
 
+static int __init x86_xsaveopt_setup(char *s)
+{
+	setup_clear_cpu_cap(X86_FEATURE_XSAVEOPT);
+	return 1;
+}
+__setup("noxsaveopt", x86_xsaveopt_setup);
+
 #ifdef CONFIG_X86_32
 static int cachesize_override __cpuinitdata = -1;
 static int disable_x86_serial_nr __cpuinitdata = 1;
Index: tip/arch/x86/include/asm/i387.h
===================================================================
--- tip.orig/arch/x86/include/asm/i387.h
+++ tip/arch/x86/include/asm/i387.h
@@ -60,7 +60,7 @@ extern int restore_i387_xstate_ia32(void
 
 static __always_inline __pure bool use_xsaveopt(void)
 {
-	return 0;
+	return static_cpu_has(X86_FEATURE_XSAVEOPT);
 }
 
 static __always_inline __pure bool use_xsave(void)