Re: [PATCH RFC 0/2] x86/fpu: avoid "xstate_fault" in xsave_user/xrestore_user

[Borislav Petkov <bp@suse.de>]

On Tue, Mar 17, 2015 at 11:00:46AM +0100, Quentin Casasnovas wrote:
> Fair point, but AFAIUI we can't do check_insn(XSAVES) alone as of today,
> and the "..." in your "check_isns(XSAVEOPT, ...)" code above would still
> need to contain the outputs operands.

I think we can do this (see diff the end of this mail).

It still explodes my guest with:

[    2.940379] Freeing unused kernel memory: 2860K (ffffffff81a39000 - ffffffff81d04000)
[    2.980722] Kernel panic - not syncing: Attempted to kill init! exitcode=0x0000000b
[    2.980722] 
[    2.984096] CPU: 1 PID: 1 Comm: init Not tainted 4.0.0-rc3+ #22
[    2.984096] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.7.5-20140531_083030-gandalf 04/01/2014
[    2.984096]  ffff88007bcf0000 ffff88007bcfbc58 ffffffff81675eb9 0000000000000001
[    2.984096]  ffffffff818a9ae8 ffff88007bcfbcd8 ffffffff816745be ffff88007bcf0000
[    2.984096]  0000000000000010 ffff88007bcfbce8 ffff88007bcfbc88 ffff88007bfcc0b0
[    2.984096] Call Trace:
[    2.984096]  [<ffffffff81675eb9>] dump_stack+0x4f/0x7b
[    2.984096]  [<ffffffff816745be>] panic+0xc0/0x1dc
[    2.984096]  [<ffffffff81056143>] do_exit+0xc13/0xc50
[    2.984096]  [<ffffffff810574a4>] do_group_exit+0x54/0xe0
[    2.984096]  [<ffffffff81065526>] get_signal+0x266/0xab0
[    2.984096]  [<ffffffff81002523>] do_signal+0x33/0xba0
[    2.984096]  [<ffffffff8109c88e>] ? put_lock_stats.isra.19+0xe/0x30
[    2.984096]  [<ffffffff8167dd81>] ? _raw_spin_unlock_irqrestore+0x41/0x80
[    2.984096]  [<ffffffff8167dd8b>] ? _raw_spin_unlock_irqrestore+0x4b/0x80
[    2.984096]  [<ffffffff8167f9f1>] ? retint_signal+0x11/0x90
[    2.984096]  [<ffffffff810030f5>] do_notify_resume+0x65/0x80
[    2.984096]  [<ffffffff8167fa26>] retint_signal+0x46/0x90
[    2.984096] Kernel Offset: disabled
[    2.984096] ---[ end Kernel panic - not syncing: Attempted to kill init! exitcode=0x0000000b

because, AFAICT and from debugging so far, we call xrstor_state() without a
previous xsave_state() in that path:

[    3.304551] Freeing unused kernel memory: 2860K (ffffffff81a39000 - ffffffff81d04000)
[    3.346556] traps: xrstor_state
[    3.350418] CPU: 1 PID: 1 Comm: init Not tainted 4.0.0-rc3+ #21
[    3.350418] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.7.5-20140531_083030-gandalf 04/01/2014
[    3.350418]  ffff88007b454000 ffff88007bcfbf18 ffffffff81676079 0000000000000000
[    3.350418]  ffff88007bcf0000 ffff88007bcfbf38 ffffffff810038b6 0000000000000000
[    3.350418]  00007f6b95ba91c8 ffff88007bcfbf48 ffffffff81004433 00007ffeecd31bb0
[    3.350418] Call Trace:
[    3.350418]  [<ffffffff81676079>] dump_stack+0x4f/0x7b
[    3.350418]  [<ffffffff810038b6>] math_state_restore+0xa6/0x220
[    3.350418]  [<ffffffff81004433>] do_device_not_available+0x23/0x30
[    3.350418]  [<ffffffff81680865>] device_not_available+0x15/0x20

so I need to sort that one out first.

But including the fault exception table in the macro is already an
improvement IMO.

Thanks.

---
diff --git a/arch/x86/include/asm/xsave.h b/arch/x86/include/asm/xsave.h
index c9a6d68b8d62..0d0cc053c7cc 100644
--- a/arch/x86/include/asm/xsave.h
+++ b/arch/x86/include/asm/xsave.h
@@ -67,6 +67,51 @@ extern int init_fpu(struct task_struct *child);
 			_ASM_EXTABLE(1b, 3b)		\
 			: [err] "=r" (err)
 
+#define XSTATE_OP(op, st, lmask, hmask, err)				\
+	asm volatile("1:" op "\n\t"					\
+		     "2:\n\t"						\
+		     ".pushsection .fixup,\"ax\"\n\t"			\
+		     "3: movl $-1,%[err]\n\t"				\
+		     "jmp 2b\n\t"					\
+		     ".popsection\n\t"					\
+		     _ASM_EXTABLE(1b, 3b)				\
+		     : [err] "=r" (err)					\
+		     : "D" (st), "m" (*st), "a" (lmask), "d" (hmask)	\
+		     : "memory")
+
+/*
+ * 661 and alt_end_marker labels below are defined in ALTERNATIVE*
+ * and we're reusing  them here so as not to clutter this macro
+ * unnecessarily.
+ */
+#define XSTATE_XSAVE(st, lmask, hmask, err)				\
+	asm volatile(ALTERNATIVE_2(XSAVE,				\
+				   XSAVEOPT, X86_FEATURE_XSAVEOPT,	\
+				   XSAVES,   X86_FEATURE_XSAVES)	\
+		     "\n"						\
+		     ".pushsection .fixup,\"ax\"\n"			\
+		     "3: movl $-1, %[err]\n"				\
+		     "jmp " alt_end_marker "b\n"			\
+		     ".popsection\n"					\
+		     _ASM_EXTABLE(661b, 3b)				\
+		     : [err] "=r" (err)					\
+		     : "D" (st), "a" (lmask), "d" (hmask)		\
+		     : "memory")
+
+#define XSTATE_XRESTORE(st, lmask, hmask, err)				\
+	asm volatile(ALTERNATIVE(XRSTOR,				\
+				 XRSTORS, X86_FEATURE_XSAVES)		\
+		     "\n"						\
+		     ".pushsection .fixup,\"ax\"\n"			\
+		     "3: movl $-1, %[err]\n"				\
+		     "jmp 663b\n"					\
+		     ".popsection\n"					\
+		     _ASM_EXTABLE(661b, 3b)				\
+		     : [err] "=r" (err)					\
+		     : "D" (st), "m" (*st), "a" (lmask), "d" (hmask)	\
+		     : "memory")
+
+
 /*
  * This function is called only during boot time when x86 caps are not set
  * up and alternative can not be used yet.
@@ -77,20 +122,11 @@ static inline int xsave_state_booting(struct xsave_struct *fx, u64 mask)
 	u32 hmask = mask >> 32;
 	int err = 0;
 
-	WARN_ON(system_state != SYSTEM_BOOTING);
-
-	if (boot_cpu_has(X86_FEATURE_XSAVES))
-		asm volatile("1:"XSAVES"\n\t"
-			"2:\n\t"
-			     xstate_fault
-			: "D" (fx), "m" (*fx), "a" (lmask), "d" (hmask)
-			:   "memory");
+	if (static_cpu_has_safe(X86_FEATURE_XSAVES))
+		XSTATE_OP(XSAVES, fx, lmask, hmask, err);
 	else
-		asm volatile("1:"XSAVE"\n\t"
-			"2:\n\t"
-			     xstate_fault
-			: "D" (fx), "m" (*fx), "a" (lmask), "d" (hmask)
-			:   "memory");
+		XSTATE_OP(XSAVE, fx, lmask, hmask, err);
+
 	return err;
 }
 
@@ -104,20 +140,12 @@ static inline int xrstor_state_booting(struct xsave_struct *fx, u64 mask)
 	u32 hmask = mask >> 32;
 	int err = 0;
 
-	WARN_ON(system_state != SYSTEM_BOOTING);
+       WARN_ON(system_state != SYSTEM_BOOTING);
 
-	if (boot_cpu_has(X86_FEATURE_XSAVES))
-		asm volatile("1:"XRSTORS"\n\t"
-			"2:\n\t"
-			     xstate_fault
-			: "D" (fx), "m" (*fx), "a" (lmask), "d" (hmask)
-			:   "memory");
+	if (static_cpu_has_safe(X86_FEATURE_XSAVES))
+		XSTATE_OP(XRSTORS, fx, lmask, hmask, err);
 	else
-		asm volatile("1:"XRSTOR"\n\t"
-			"2:\n\t"
-			     xstate_fault
-			: "D" (fx), "m" (*fx), "a" (lmask), "d" (hmask)
-			:   "memory");
+		XSTATE_OP(XRSTOR, fx, lmask, hmask, err);
 	return err;
 }
 
@@ -141,18 +169,7 @@ static inline int xsave_state(struct xsave_struct *fx, u64 mask)
 	 *
 	 * If none of xsaves and xsaveopt is enabled, use xsave.
 	 */
-	alternative_input_2(
-		"1:"XSAVE,
-		XSAVEOPT,
-		X86_FEATURE_XSAVEOPT,
-		XSAVES,
-		X86_FEATURE_XSAVES,
-		[fx] "D" (fx), "a" (lmask), "d" (hmask) :
-		"memory");
-	asm volatile("2:\n\t"
-		     xstate_fault
-		     : "0" (0)
-		     : "memory");
+	XSTATE_XSAVE(fx, lmask, hmask, err);
 
 	return err;
 }
@@ -170,17 +187,7 @@ static inline int xrstor_state(struct xsave_struct *fx, u64 mask)
 	 * Use xrstors to restore context if it is enabled. xrstors supports
 	 * compacted format of xsave area which is not supported by xrstor.
 	 */
-	alternative_input(
-		"1: " XRSTOR,
-		XRSTORS,
-		X86_FEATURE_XSAVES,
-		"D" (fx), "m" (*fx), "a" (lmask), "d" (hmask)
-		: "memory");
-
-	asm volatile("2:\n"
-		     xstate_fault
-		     : "0" (0)
-		     : "memory");
+	XSTATE_XRESTORE(fx, lmask, hmask, err);
 
 	return err;
 }

-- 
Regards/Gruss,
    Boris.

ECO tip #101: Trim your mails when you reply.
--