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s390/fpu: Add fpc exception handler / remove fixup section again

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The fixup section was added again by mistake when test_fp_ctl() was
removed. The reason for the removal of the fixup section is described in
commit 484a8ed8b7 ("s390/extable: add dedicated uaccess handler").
Remove it again for the same reason.

Add an exception handler which handles exceptions when the floating point
control register is attempted to be set to invalid values. The exception
handler sets the floating point control register to zero and continues
execution at the specified address.

The new sfpc inline assembly is open-coded to make back porting a bit
easier.

Fixes: 702644249d ("s390/fpu: get rid of test_fp_ctl()")
Cc: stable@vger.kernel.org
Reviewed-by: Alexander Gordeev <agordeev@linux.ibm.com>
Signed-off-by: Heiko Carstens <hca@linux.ibm.com>
Signed-off-by: Alexander Gordeev <agordeev@linux.ibm.com>
This commit is contained in:
Heiko Carstens 2025-01-10 11:52:17 +01:00 committed by Alexander Gordeev
parent f684b7954e
commit ae02615b7f
4 changed files with 17 additions and 12 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

4
arch/s390/include/asm/asm-extable.h
View File

@ -14,6 +14,7 @@
#define EX_TYPE_UA_LOAD_REG 5
#define EX_TYPE_UA_LOAD_REGPAIR 6
#define EX_TYPE_ZEROPAD 7
#define EX_TYPE_FPC 8
#define EX_DATA_REG_ERR_SHIFT 0
#define EX_DATA_REG_ERR GENMASK(3, 0)
@ -84,4 +85,7 @@
#define EX_TABLE_ZEROPAD(_fault, _target, _regdata, _regaddr) \
__EX_TABLE(__ex_table, _fault, _target, EX_TYPE_ZEROPAD, _regdata, _regaddr, 0)
#define EX_TABLE_FPC(_fault, _target) \
__EX_TABLE(__ex_table, _fault, _target, EX_TYPE_FPC, __stringify(%%r0), __stringify(%%r0), 0)
#endif /* __ASM_EXTABLE_H */

15
arch/s390/include/asm/fpu-insn.h
View File

@ -100,19 +100,12 @@ static __always_inline void fpu_lfpc(unsigned int *fpc)
*/
static inline void fpu_lfpc_safe(unsigned int *fpc)
{
u32 tmp;
instrument_read(fpc, sizeof(*fpc));
asm_inline volatile(
"0: lfpc %[fpc]\n"
"1: nopr %%r7\n"
".pushsection .fixup, \"ax\"\n"
"2: lghi %[tmp],0\n"
" sfpc %[tmp]\n"
" jg 1b\n"
".popsection\n"
EX_TABLE(1b, 2b)
: [tmp] "=d" (tmp)
" lfpc %[fpc]\n"
"0: nopr %%r7\n"
EX_TABLE_FPC(0b, 0b)
:
: [fpc] "Q" (*fpc)
: "memory");
}

1
arch/s390/kernel/vmlinux.lds.S
View File

@ -52,7 +52,6 @@ SECTIONS
SOFTIRQENTRY_TEXT
FTRACE_HOTPATCH_TRAMPOLINES_TEXT
*(.text.*_indirect_*)
*(.fixup)
*(.gnu.warning)
. = ALIGN(PAGE_SIZE);
_etext = .; /* End of text section */

9
arch/s390/mm/extable.c
View File

@ -77,6 +77,13 @@ static bool ex_handler_zeropad(const struct exception_table_entry *ex, struct pt
return true;
}
static bool ex_handler_fpc(const struct exception_table_entry *ex, struct pt_regs *regs)
{
asm volatile("sfpc %[val]\n" : : [val] "d" (0));
regs->psw.addr = extable_fixup(ex);
return true;
}
bool fixup_exception(struct pt_regs *regs)
{
const struct exception_table_entry *ex;
@ -99,6 +106,8 @@ bool fixup_exception(struct pt_regs *regs)
return ex_handler_ua_load_reg(ex, true, regs);
case EX_TYPE_ZEROPAD:
return ex_handler_zeropad(ex, regs);
case EX_TYPE_FPC:
return ex_handler_fpc(ex, regs);
}
panic("invalid exception table entry");
}