Sven Schnelle b61b159512 s390: add stack for machine check handler ... The previous code used the normal kernel stack for machine checks. This is problematic when a machine check interrupts a system call or interrupt handler right at the beginning where registers are set up. Assume system_call is interrupted at the first instruction and a machine check is triggered. The machine check handler is called, checks the PSW to see whether it is coming from user space, notices that it is already in kernel mode but %r15 still contains the user space stack. This would lead to a kernel crash. There are basically two ways of fixing that: Either using the 'critical cleanup' approach which compares the address in the PSW to see whether it is already at a point where the stack has been set up, or use an extra stack for the machine check handler. For simplicity, we will go with the second approach and allocate an extra stack. This adds some memory overhead for large systems, but usually large system have plenty of memory so this isn't really a concern. But it keeps the mchk stack setup simple and less error prone. Fixes: 0b0ed657fe ("s390: remove critical section cleanup from entry.S") Signed-off-by: Sven Schnelle <svens@linux.ibm.com> Cc: <stable@kernel.org> # v5.8+ Reviewed-by: Heiko Carstens <hca@linux.ibm.com> Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>		2021-02-13 17:17:53 +01:00
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asm	s390: add stack for machine check handler	2021-02-13 17:17:53 +01:00
uapi/asm	s390: convert to generic entry	2021-01-19 12:29:26 +01:00