kernel.git/arch/s390/kernel/entry.S, branch linux-5.13.y

s390: clear pt_regs::flags on irq entry

2021-06-21T09:19:18Z

The current irq entry code doesn't initialize pt_regs::flags. On exit to user mode arch_do_signal_or_restart() tests whether PIF_SYSCALL is set, which might yield wrong results. Fix this by clearing pt_regs::flags in the entry.S irq handler code. Reported-by: Heiko Carstens Signed-off-by: Sven Schnelle Reviewed-by: Heiko Carstens Fixes: 56e62a737028 ("s390: convert to generic entry") Cc: # 5.12 Signed-off-by: Vasily Gorbik

s390/mcck: fix invalid KVM guest condition check

2021-06-07T10:12:03Z

Wrong condition check is used to decide if a machine check hit while in KVM guest. As result of this check the instruction following the SIE critical section might be considered as still in KVM guest and _CIF_MCCK_GUEST CPU flag mistakenly set as result. Fixes: c929500d7a5a ("s390/nmi: s390: New low level handling for machine check happening in guest") Cc: Signed-off-by: Alexander Gordeev Reviewed-by: Christian Borntraeger Signed-off-by: Heiko Carstens Signed-off-by: Vasily Gorbik

s390/mcck: fix calculation of SIE critical section size

2021-06-07T10:12:03Z

The size of SIE critical section is calculated wrongly as result of a missed subtraction in commit 0b0ed657fe00 ("s390: remove critical section cleanup from entry.S") Fixes: 0b0ed657fe00 ("s390: remove critical section cleanup from entry.S") Cc: Signed-off-by: Alexander Gordeev Reviewed-by: Christian Borntraeger Signed-off-by: Heiko Carstens Signed-off-by: Vasily Gorbik

s390/entry: save the caller of psw_idle

2021-04-12T10:44:31Z

Currently psw_idle does not allocate a stack frame and does not save its r14 and r15 into the save area. Even though this is valid from call ABI point of view, because psw_idle does not make any calls explicitly, in reality psw_idle is an entry point for controlled transition into serving interrupts. So, in practice, psw_idle stack frame is analyzed during stack unwinding. Depending on build options that r14 slot in the save area of psw_idle might either contain a value saved by previous sibling call or complete garbage. [task 0000038000003c28] do_ext_irq+0xd6/0x160 [task 0000038000003c78] ext_int_handler+0xba/0xe8 [task *0000038000003dd8] psw_idle_exit+0x0/0x8 <-- pt_regs ([task 0000038000003dd8] 0x0) [task 0000038000003e10] default_idle_call+0x42/0x148 [task 0000038000003e30] do_idle+0xce/0x160 [task 0000038000003e70] cpu_startup_entry+0x36/0x40 [task 0000038000003ea0] arch_call_rest_init+0x76/0x80 So, to make a stacktrace nicer and actually point for the real caller of psw_idle in this frequently occurring case, make psw_idle save its r14. [task 0000038000003c28] do_ext_irq+0xd6/0x160 [task 0000038000003c78] ext_int_handler+0xba/0xe8 [task *0000038000003dd8] psw_idle_exit+0x0/0x6 <-- pt_regs ([task 0000038000003dd8] arch_cpu_idle+0x3c/0xd0) [task 0000038000003e10] default_idle_call+0x42/0x148 [task 0000038000003e30] do_idle+0xce/0x160 [task 0000038000003e70] cpu_startup_entry+0x36/0x40 [task 0000038000003ea0] arch_call_rest_init+0x76/0x80 Reviewed-by: Sven Schnelle Signed-off-by: Vasily Gorbik Signed-off-by: Heiko Carstens

s390/entry: avoid setting up backchain in ext|io handlers

2021-04-12T10:44:30Z

Currently when interrupt arrives to cpu while in kernel context INT_HANDLER macro (used for ext_int_handler and io_int_handler) allocates new stack frame and pt_regs on the kernel stack and sets up the backchain to jump over the pt_regs to the frame which has been interrupted. This is not ideal to two reasons: 1. This hides the fact that kernel stack contains interrupt frame in it and hence breaks arch_stack_walk_reliable(), which needs to know that to guarantee "reliability" and checks that there are no pt_regs on the way. 2. It breaks the backchain unwinder logic, which assumes that the next stack frame after an interrupt frame is reliable, while it is not. In some cases (when r14 contains garbage) this leads to early unwinding termination with an error, instead of marking frame as unreliable and continuing. To address that, only set backchain to 0. Fixes: 56e62a737028 ("s390: convert to generic entry") Reviewed-by: Sven Schnelle Signed-off-by: Vasily Gorbik Signed-off-by: Heiko Carstens

s390: split cleanup_sie

2021-02-13T16:17:53Z

The current code uses the address in %r11 to figure out whether it was called from the machine check handler or from a normal interrupt handler. Instead of doing this implicit logic (which is mostly a leftover from the old critical cleanup approach) just add a second label and use that. Signed-off-by: Sven Schnelle Reviewed-by: Heiko Carstens Signed-off-by: Vasily Gorbik

s390: use r13 in cleanup_sie as temp register

2021-02-13T16:17:53Z

Instead of thrashing r11 which is normally our pointer to struct pt_regs on the stack, use r13 as temporary register in the BR_EX macro. r13 is already used in cleanup_sie, so no need to thrash another register. Signed-off-by: Sven Schnelle Reviewed-by: Heiko Carstens Signed-off-by: Vasily Gorbik

s390: fix kernel asce loading when sie is interrupted

2021-02-13T16:17:53Z

If a machine check is coming in during sie, the PU saves the control registers to the machine check save area. Afterwards mcck_int_handler is called, which loads __LC_KERNEL_ASCE into %cr1. Later the code restores %cr1 from the machine check area, but that is wrong when SIE was interrupted because the machine check area still contains the gmap asce. Instead it should return with either __KERNEL_ASCE in %cr1 when interrupted in SIE or the previous %cr1 content saved in the machine check save area. Fixes: 87d598634521 ("s390/mm: remove set_fs / rework address space handling") Signed-off-by: Sven Schnelle Cc: # v5.8+ Reviewed-by: Heiko Carstens Signed-off-by: Vasily Gorbik

s390: add stack for machine check handler

2021-02-13T16:17:53Z

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: 0b0ed657fe00 ("s390: remove critical section cleanup from entry.S") Signed-off-by: Sven Schnelle Cc: # v5.8+ Reviewed-by: Heiko Carstens Signed-off-by: Vasily Gorbik

s390: open code SWITCH_KERNEL macro

2021-02-13T16:17:53Z

This is a preparation patch for two later bugfixes. In the past both int_handler and machine check handler used SWITCH_KERNEL to switch to the kernel stack. However, SWITCH_KERNEL doesn't work properly in machine check context. So instead of adding more complexity to this macro, just remove it. Signed-off-by: Sven Schnelle Cc: # v5.8+ Reviewed-by: Heiko Carstens Signed-off-by: Vasily Gorbik