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Asked: 2026-05-28T07:30:54+00:00

On the s390 architecture virtual kernel and user address spaces are never present at

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On the s390 architecture virtual kernel and user address spaces are never present at the same time, so how does copy_to_user work?

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  1. Editorial Team

    copy_to_user for s390 is implemented here: linux/arch/s390/include/asm/uaceess.h.

    uaccess is the pointer to copy_[to/from]_user actual implementation. It is setted up here (grep uaccess): arch/s390/kernel/setup.c. There are 4 implementations of uaccess, depening from mode:

    uaccess_mvcos_switch, uaccess_pt, uaccess_mvcos and uaccess_std

    For example uaccess_std is here: http://lxr.linux.no/#linux+v3.2.1/arch/s390/lib/uaccess_std.c

    4 *  Standard user space access functions based on mvcp/mvcs and doing
5 *  interesting things in the secondary space mode.

    …

    82 size_t copy_to_user_std(size_t size, void __user *ptr, const void *x)
83 {
84        unsigned long tmp1, tmp2;
85
86        tmp1 = -256UL;
87        asm volatile(
88                "0: mvcs  0(%0,%1),0(%2),%3\n"

    The mvcp/mvcs mechanism is used:
    http://publib.boulder.ibm.com/infocenter/zos/v1r11/topic/com.ibm.zos.r11.ieaa500/iea2a57031.htm

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