backport new FPU register copy helpers

This allows us to fix the ZFS SIMD patch for 5.0 kernel way easier.

Signed-off-by: Thomas Lamprecht <[email protected]>

patches/kernel/0007-x86-fpu-backport-copy_kernel_to_XYZ_err-helpers.patch

@@ -0,0 +1,103 @@
+From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
+From: Thomas Lamprecht <[email protected]>
+Date: Wed, 3 Apr 2019 18:41:50 +0200
+Subject: [PATCH] x86/fpu: backport copy_kernel_to_XYZ_err helpers
+MIME-Version: 1.0
+Content-Type: text/plain; charset=UTF-8
+Content-Transfer-Encoding: 8bit
+
+partial cherry-pick from upstream 5.2 "86/fpu: Restore from kernel
+memory on the 64-bit path too"
+commit 926b21f37b072ae4c117052de45a975c6d468fec
+Author: Sebastian Andrzej Siewior <[email protected]>
+
+Namely, only backport the added helpers, none of the semantic changes.
+
+relevant parts of the original commit message:
+> In order to avoid that mess, copy the FPU state from userland, validate
+> it and then load it. The copy_kernel_…() helpers are basically just
+> like the old helpers except that they operate on kernel memory and the
+> fault handler just sets the error value and the caller handles it.
+
+Link: https://lkml.kernel.org/r/[email protected]
+(partial cherry picked from commit 926b21f37b072ae4c117052de45a975c6d468fec)
+Signed-off-by: Thomas Lamprecht <[email protected]>
+---
+ arch/x86/include/asm/fpu/internal.h | 43 +++++++++++++++++++++++++++++
+ 1 file changed, 43 insertions(+)
+
+diff --git a/arch/x86/include/asm/fpu/internal.h b/arch/x86/include/asm/fpu/internal.h
+index fa2c93cb42a2..f3193ab0a2fb 100644
+--- a/arch/x86/include/asm/fpu/internal.h
++++ b/arch/x86/include/asm/fpu/internal.h
+@@ -122,6 +122,21 @@ extern void fpstate_sanitize_xstate(struct fpu *fpu);
+ 	err;								\
+ })
+ 
++#define kernel_insn_err(insn, output, input...)				\
++({									\
++	int err;							\
++	asm volatile("1:" #insn "\n\t"					\
++		     "2:\n"						\
++		     ".section .fixup,\"ax\"\n"				\
++		     "3:  movl $-1,%[err]\n"				\
++		     "    jmp  2b\n"					\
++		     ".previous\n"					\
++		     _ASM_EXTABLE(1b, 3b)				\
++		     : [err] "=r" (err), output				\
++		     : "0"(0), input);					\
++	err;								\
++})
++
+ #define kernel_insn(insn, output, input...)				\
+ 	asm volatile("1:" #insn "\n\t"					\
+ 		     "2:\n"						\
+@@ -158,6 +173,14 @@ static inline void copy_kernel_to_fxregs(struct fxregs_state *fx)
+ 	}
+ }
+ 
++static inline int copy_kernel_to_fxregs_err(struct fxregs_state *fx)
++{
++	if (IS_ENABLED(CONFIG_X86_32))
++		return kernel_insn_err(fxrstor %[fx], "=m" (*fx), [fx] "m" (*fx));
++	else
++		return kernel_insn_err(fxrstorq %[fx], "=m" (*fx), [fx] "m" (*fx));
++}
++
+ static inline int copy_user_to_fxregs(struct fxregs_state __user *fx)
+ {
+ 	if (IS_ENABLED(CONFIG_X86_32))
+@@ -175,6 +198,11 @@ static inline void copy_kernel_to_fregs(struct fregs_state *fx)
+ 	kernel_insn(frstor %[fx], "=m" (*fx), [fx] "m" (*fx));
+ }
+ 
++static inline int copy_kernel_to_fregs_err(struct fregs_state *fx)
++{
++	return kernel_insn_err(frstor %[fx], "=m" (*fx), [fx] "m" (*fx));
++}
++
+ static inline int copy_user_to_fregs(struct fregs_state __user *fx)
+ {
+ 	return user_insn(frstor %[fx], "=m" (*fx), [fx] "m" (*fx));
+@@ -400,6 +428,21 @@ static inline int copy_user_to_xregs(struct xregs_state __user *buf, u64 mask)
+ 	return err;
+ }
+ 
++/*
++ * Restore xstate from kernel space xsave area, return an error code instead of
++ * an exception.
++ */
++static inline int copy_kernel_to_xregs_err(struct xregs_state *xstate, u64 mask)
++{
++	u32 lmask = mask;
++	u32 hmask = mask >> 32;
++	int err;
++
++	XSTATE_OP(XRSTOR, xstate, lmask, hmask, err);
++
++	return err;
++}
++
+ /*
+  * These must be called with preempt disabled. Returns
+  * 'true' if the FPU state is still intact and we can