x86/mce: Drop copyin special case for #MC

mainline inclusion
from mainline-v5.16-rc1
commit 69065847
category: bugfix
bugzilla: https://gitee.com/openeuler/intel-kernel/issues/I5HAC1
CVE: NA

Intel-SIG: commit 69065847 x86/mce: Drop copyin special case for #MC.
Backport for MCA recovery enhancing & bug fix.

--------------------------------

Fixes to the iterator code to handle faults that are not on page
boundaries mean that the special case for machine check during copy from
user is no longer needed.

For a full list of those fixes, see the output of:

  git log --oneline v5.14 ^v5.13 -- lib/iov_iter.c

Intel-SIG: commit 69065847 x86/mce: Drop copyin special case for #MC.
backport for MCA recovery enhance and bug fix.
Signed-off-by: NTony Luck <tony.luck@intel.com>
Signed-off-by: NBorislav Petkov <bp@suse.de>
Link: https://lkml.kernel.org/r/20210818002942.1607544-4-tony.luck@intel.comSigned-off-by: NYouquan Song <youquan.song@intel.com>
Signed-off-by: NJason Zeng <jason.zeng@intel.com>

arch/x86/lib/copy_user_64.S

@@ -234,24 +234,11 @@ EXPORT_SYMBOL(copy_user_enhanced_fast_string)
  */
 SYM_CODE_START_LOCAL(.Lcopy_user_handle_tail)
 	movl %edx,%ecx
-	cmp $X86_TRAP_MC,%eax		/* check if X86_TRAP_MC */
-	je 3f
 1:	rep movsb
 2:	mov %ecx,%eax
 	ASM_CLAC
 	ret
 
-	/*
-	 * Return zero to pretend that this copy succeeded. This
-	 * is counter-intuitive, but needed to prevent the code
-	 * in lib/iov_iter.c from retrying and running back into
-	 * the poison cache line again. The machine check handler
-	 * will ensure that a SIGBUS is sent to the task.
-	 */
-3:	xorl %eax,%eax
-	ASM_CLAC
-	ret
-
 	_ASM_EXTABLE_CPY(1b, 2b)
 SYM_CODE_END(.Lcopy_user_handle_tail)