s390: Revert support for DCACHE_WORD_ACCESS

load_unaligned_zeropad() reads eight bytes from unaligned addresses and may
cross page boundaries. It handles exceptions which may happen if reading
from the second page results in an exception.

For pages which are donated to the Ultravisor for secure execution purposes
the do_secure_storage_access() exception handler however does not handle
such exceptions correctly. Such an exception may result in an endless
exception loop which will never be resolved.

An attempt to fix this [1] turned out to be not sufficient. For now revert
load_unaligned_zeropad() until this problem has been resolved in a proper
way.

Note that the implementation of load_unaligned_zeropad() itself is
correct. The revert is just a temporary workaround until there is complete
fix for secure storage access exceptions.

[1] commit b00be77302d7 ("s390/mm: Add missing secure storage access fixups for donated memory")

Fixes: 802ba53eefc5 ("s390: add support for DCACHE_WORD_ACCESS")
Cc: stable@vger.kernel.org
Acked-by: Christian Borntraeger <borntraeger@linux.ibm.com>
Signed-off-by: Heiko Carstens <hca@linux.ibm.com>
Signed-off-by: Alexander Gordeev <agordeev@linux.ibm.com>

diff --git a/arch/s390/Kconfig b/arch/s390/Kconfig
index fe5eeba..33988cc 100644 (file)
--- a/arch/s390/Kconfig
+++ b/arch/s390/Kconfig
@@ -166,7 +166,6 @@ config S390
        select ARCH_WANTS_THP_SWAP
        select BUILDTIME_TABLE_SORT
        select CLONE_BACKWARDS2
-       select DCACHE_WORD_ACCESS if !KMSAN
        select DYNAMIC_FTRACE if FUNCTION_TRACER
        select FUNCTION_ALIGNMENT_8B if CC_IS_GCC
        select FUNCTION_ALIGNMENT_16B if !CC_IS_GCC

diff --git a/arch/s390/include/asm/asm-extable.h b/arch/s390/include/asm/asm-extable.h
index d23ea0c..99748c2 100644 (file)
--- a/arch/s390/include/asm/asm-extable.h
+++ b/arch/s390/include/asm/asm-extable.h
@@ -12,7 +12,6 @@
 #define EX_TYPE_UA_FAULT       3
 #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_TYPE_UA_MVCOS_TO    9
 #define EX_TYPE_UA_MVCOS_FROM  10
@@ -80,9 +79,6 @@
 #define EX_TABLE_UA_LOAD_REGPAIR(_fault, _target, _regerr, _regzero)   \
        __EX_TABLE(__ex_table, _fault, _target, EX_TYPE_UA_LOAD_REGPAIR, _regerr, _regzero, 0)
 
-#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)
 

diff --git a/arch/s390/include/asm/word-at-a-time.h b/arch/s390/include/asm/word-at-a-time.h
index eaa19de..e928703 100644 (file)
--- a/arch/s390/include/asm/word-at-a-time.h
+++ b/arch/s390/include/asm/word-at-a-time.h
@@ -4,7 +4,6 @@
 
 #include <linux/bitops.h>
 #include <linux/wordpart.h>
-#include <asm/asm-extable.h>
 #include <asm/bitsperlong.h>
 
 struct word_at_a_time {
@@ -41,25 +40,4 @@ static inline unsigned long zero_bytemask(unsigned long data)
        return ~1UL << data;
 }
 
-/*
- * Load an unaligned word from kernel space.
- *
- * In the (very unlikely) case of the word being a page-crosser
- * and the next page not being mapped, take the exception and
- * return zeroes in the non-existing part.
- */
-static inline unsigned long load_unaligned_zeropad(const void *addr)
-{
-       unsigned long data;
-
-       asm_inline volatile(
-               "0:     lg      %[data],0(%[addr])\n"
-               "1:     nopr    %%r7\n"
-               EX_TABLE_ZEROPAD(0b, 1b, %[data], %[addr])
-               EX_TABLE_ZEROPAD(1b, 1b, %[data], %[addr])
-               : [data] "=d" (data)
-               : [addr] "a" (addr), "m" (*(unsigned long *)addr));
-       return data;
-}
-
 #endif /* _ASM_WORD_AT_A_TIME_H */

diff --git a/arch/s390/mm/extable.c b/arch/s390/mm/extable.c
index 7498e85..063b434 100644 (file)
--- a/arch/s390/mm/extable.c
+++ b/arch/s390/mm/extable.c
@@ -50,22 +50,6 @@ static bool ex_handler_ua_load_reg(const struct exception_table_entry *ex,
        return true;
 }
 
-static bool ex_handler_zeropad(const struct exception_table_entry *ex, struct pt_regs *regs)
-{
-       unsigned int reg_addr = FIELD_GET(EX_DATA_REG_ADDR, ex->data);
-       unsigned int reg_data = FIELD_GET(EX_DATA_REG_ERR, ex->data);
-       unsigned long data, addr, offset;
-
-       addr = regs->gprs[reg_addr];
-       offset = addr & (sizeof(unsigned long) - 1);
-       addr &= ~(sizeof(unsigned long) - 1);
-       data = *(unsigned long *)addr;
-       data <<= BITS_PER_BYTE * offset;
-       regs->gprs[reg_data] = data;
-       regs->psw.addr = extable_fixup(ex);
-       return true;
-}
-
 static bool ex_handler_fpc(const struct exception_table_entry *ex, struct pt_regs *regs)
 {
        fpu_sfpc(0);
@@ -134,8 +118,6 @@ bool fixup_exception(struct pt_regs *regs)
                return ex_handler_ua_load_reg(ex, false, regs);
        case EX_TYPE_UA_LOAD_REGPAIR:
                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);
        case EX_TYPE_UA_MVCOS_TO: