Merge tag 'x86_cpu_for_v6.1_rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

Pull x86 cpu updates from Borislav Petkov:

 - Print the CPU number at segfault time.

   The number printed is not always accurate (preemption is enabled at
   that time) but the print string contains "likely" and after a lot of
   back'n'forth on this, this was the consensus that was reached. See
   thread at [1].

 - After a *lot* of testing and polishing, finally the clear_user()
   improvements to inline REP; STOSB by default

Link: https://lore.kernel.org/r/5d62c1d0-7425-d5bb-ecb5-1dc3b4d7d245@intel.com [1]

* tag 'x86_cpu_for_v6.1_rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
  x86/mm: Print likely CPU at segfault time
  x86/clear_user: Make it faster

1 files changed, 138 insertions, 0 deletions

diff --git a/arch/x86/lib/clear_page_64.S b/arch/x86/lib/clear_page_64.S
index fe59b8ac4fcc..ecbfb4dd3b01 100644
--- a/arch/x86/lib/clear_page_64.S
+++ b/arch/x86/lib/clear_page_64.S
@@ -1,5 +1,6 @@
 /* SPDX-License-Identifier: GPL-2.0-only */
 #include <linux/linkage.h>
+#include <asm/asm.h>
 #include <asm/export.h>
 
 /*
@@ -50,3 +51,140 @@ SYM_FUNC_START(clear_page_erms)
 	RET
 SYM_FUNC_END(clear_page_erms)
 EXPORT_SYMBOL_GPL(clear_page_erms)
+
+/*
+ * Default clear user-space.
+ * Input:
+ * rdi destination
+ * rcx count
+ *
+ * Output:
+ * rcx: uncleared bytes or 0 if successful.
+ */
+SYM_FUNC_START(clear_user_original)
+	/*
+	 * Copy only the lower 32 bits of size as that is enough to handle the rest bytes,
+	 * i.e., no need for a 'q' suffix and thus a REX prefix.
+	 */
+	mov %ecx,%eax
+	shr $3,%rcx
+	jz .Lrest_bytes
+
+	# do the qwords first
+	.p2align 4
+.Lqwords:
+	movq $0,(%rdi)
+	lea 8(%rdi),%rdi
+	dec %rcx
+	jnz .Lqwords
+
+.Lrest_bytes:
+	and $7,  %eax
+	jz .Lexit
+
+	# now do the rest bytes
+.Lbytes:
+	movb $0,(%rdi)
+	inc %rdi
+	dec %eax
+	jnz .Lbytes
+
+.Lexit:
+	/*
+	 * %rax still needs to be cleared in the exception case because this function is called
+	 * from inline asm and the compiler expects %rax to be zero when exiting the inline asm,
+	 * in case it might reuse it somewhere.
+	 */
+        xor %eax,%eax
+        RET
+
+.Lqwords_exception:
+        # convert remaining qwords back into bytes to return to caller
+        shl $3, %rcx
+        and $7, %eax
+        add %rax,%rcx
+        jmp .Lexit
+
+.Lbytes_exception:
+        mov %eax,%ecx
+        jmp .Lexit
+
+        _ASM_EXTABLE_UA(.Lqwords, .Lqwords_exception)
+        _ASM_EXTABLE_UA(.Lbytes, .Lbytes_exception)
+SYM_FUNC_END(clear_user_original)
+EXPORT_SYMBOL(clear_user_original)
+
+/*
+ * Alternative clear user-space when CPU feature X86_FEATURE_REP_GOOD is
+ * present.
+ * Input:
+ * rdi destination
+ * rcx count
+ *
+ * Output:
+ * rcx: uncleared bytes or 0 if successful.
+ */
+SYM_FUNC_START(clear_user_rep_good)
+	# call the original thing for less than a cacheline
+	cmp $64, %rcx
+	jb clear_user_original
+
+.Lprep:
+	# copy lower 32-bits for rest bytes
+	mov %ecx, %edx
+	shr $3, %rcx
+	jz .Lrep_good_rest_bytes
+
+.Lrep_good_qwords:
+	rep stosq
+
+.Lrep_good_rest_bytes:
+	and $7, %edx
+	jz .Lrep_good_exit
+
+.Lrep_good_bytes:
+	mov %edx, %ecx
+	rep stosb
+
+.Lrep_good_exit:
+	# see .Lexit comment above
+	xor %eax, %eax
+	RET
+
+.Lrep_good_qwords_exception:
+	# convert remaining qwords back into bytes to return to caller
+	shl $3, %rcx
+	and $7, %edx
+	add %rdx, %rcx
+	jmp .Lrep_good_exit
+
+	_ASM_EXTABLE_UA(.Lrep_good_qwords, .Lrep_good_qwords_exception)
+	_ASM_EXTABLE_UA(.Lrep_good_bytes, .Lrep_good_exit)
+SYM_FUNC_END(clear_user_rep_good)
+EXPORT_SYMBOL(clear_user_rep_good)
+
+/*
+ * Alternative clear user-space when CPU feature X86_FEATURE_ERMS is present.
+ * Input:
+ * rdi destination
+ * rcx count
+ *
+ * Output:
+ * rcx: uncleared bytes or 0 if successful.
+ *
+ */
+SYM_FUNC_START(clear_user_erms)
+	# call the original thing for less than a cacheline
+	cmp $64, %rcx
+	jb clear_user_original
+
+.Lerms_bytes:
+	rep stosb
+
+.Lerms_exit:
+	xorl %eax,%eax
+	RET
+
+	_ASM_EXTABLE_UA(.Lerms_bytes, .Lerms_exit)
+SYM_FUNC_END(clear_user_erms)
+EXPORT_SYMBOL(clear_user_erms)