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https://git.kernel.org/pub/scm/linux/kernel/git/chenhuacai/linux-loongson
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8b72f5a97b
Reduce system call overhead time (round trip time for invoking a non-existent system call) by 25%. With the removal of set_fs() [1] lazy control register handling was removed in order to keep kernel entry and exit simple. However this made system calls slower. With the conversion to generic entry [2] and numerous follow up changes which simplified the entry code significantly, adding support for lazy asce handling doesn't add much complexity to the entry code anymore. In particular this means: - On kernel entry the primary asce is not modified and contains the user asce - Kernel accesses which require secondary-space mode (for example futex operations) are surrounded by enable_sacf_uaccess() and disable_sacf_uaccess() calls. enable_sacf_uaccess() sets the primary asce to kernel asce so that the sacf instruction can be used to switch to secondary-space mode. The primary asce is changed back to user asce with disable_sacf_uaccess(). The state of the control register which contains the primary asce is reflected with a new TIF_ASCE_PRIMARY bit. This is required on context switch so that the correct asce is restored for the scheduled in process. In result address spaces are now setup like this: CPU running in | %cr1 ASCE | %cr7 ASCE | %cr13 ASCE -----------------------------|-----------|-----------|----------- user space | user | user | kernel kernel (no sacf) | user | user | kernel kernel (during sacf uaccess) | kernel | user | kernel kernel (kvm guest execution) | guest | user | kernel In result cr1 control register content is not changed except for: - futex system calls - legacy s390 PCI system calls - the kvm specific cmpxchg_user_key() uaccess helper This leads to faster system call execution. [1]87d5986345("s390/mm: remove set_fs / rework address space handling") [2]56e62a7370("s390: convert to generic entry") Reviewed-by: Alexander Gordeev <agordeev@linux.ibm.com> Signed-off-by: Heiko Carstens <hca@linux.ibm.com>
103 lines
2.8 KiB
C
103 lines
2.8 KiB
C
/* SPDX-License-Identifier: GPL-2.0 */
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#ifndef _ASM_S390_FUTEX_H
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#define _ASM_S390_FUTEX_H
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#include <linux/instrumented.h>
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#include <linux/uaccess.h>
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#include <linux/futex.h>
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#include <asm/asm-extable.h>
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#include <asm/mmu_context.h>
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#include <asm/errno.h>
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#define FUTEX_OP_FUNC(name, insn) \
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static uaccess_kmsan_or_inline int \
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__futex_atomic_##name(int oparg, int *old, u32 __user *uaddr) \
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{ \
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bool sacf_flag; \
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int rc, new; \
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\
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instrument_copy_from_user_before(old, uaddr, sizeof(*old)); \
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sacf_flag = enable_sacf_uaccess(); \
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asm_inline volatile( \
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" sacf 256\n" \
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"0: l %[old],%[uaddr]\n" \
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"1:"insn \
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"2: cs %[old],%[new],%[uaddr]\n" \
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"3: jl 1b\n" \
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" lhi %[rc],0\n" \
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"4: sacf 768\n" \
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EX_TABLE_UA_FAULT(0b, 4b, %[rc]) \
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EX_TABLE_UA_FAULT(1b, 4b, %[rc]) \
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EX_TABLE_UA_FAULT(2b, 4b, %[rc]) \
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EX_TABLE_UA_FAULT(3b, 4b, %[rc]) \
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: [rc] "=d" (rc), [old] "=&d" (*old), \
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[new] "=&d" (new), [uaddr] "+Q" (*uaddr) \
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: [oparg] "d" (oparg) \
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: "cc"); \
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disable_sacf_uaccess(sacf_flag); \
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if (!rc) \
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instrument_copy_from_user_after(old, uaddr, sizeof(*old), 0); \
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return rc; \
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}
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FUTEX_OP_FUNC(set, "lr %[new],%[oparg]\n")
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FUTEX_OP_FUNC(add, "lr %[new],%[old]\n ar %[new],%[oparg]\n")
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FUTEX_OP_FUNC(or, "lr %[new],%[old]\n or %[new],%[oparg]\n")
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FUTEX_OP_FUNC(and, "lr %[new],%[old]\n nr %[new],%[oparg]\n")
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FUTEX_OP_FUNC(xor, "lr %[new],%[old]\n xr %[new],%[oparg]\n")
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static inline
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int arch_futex_atomic_op_inuser(int op, int oparg, int *oval, u32 __user *uaddr)
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{
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int old, rc;
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switch (op) {
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case FUTEX_OP_SET:
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rc = __futex_atomic_set(oparg, &old, uaddr);
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break;
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case FUTEX_OP_ADD:
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rc = __futex_atomic_add(oparg, &old, uaddr);
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break;
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case FUTEX_OP_OR:
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rc = __futex_atomic_or(oparg, &old, uaddr);
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break;
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case FUTEX_OP_ANDN:
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rc = __futex_atomic_and(~oparg, &old, uaddr);
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break;
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case FUTEX_OP_XOR:
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rc = __futex_atomic_xor(oparg, &old, uaddr);
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break;
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default:
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rc = -ENOSYS;
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}
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if (!rc)
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*oval = old;
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return rc;
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}
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static uaccess_kmsan_or_inline
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int futex_atomic_cmpxchg_inatomic(u32 *uval, u32 __user *uaddr, u32 oldval, u32 newval)
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{
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bool sacf_flag;
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int rc;
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instrument_copy_from_user_before(uval, uaddr, sizeof(*uval));
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sacf_flag = enable_sacf_uaccess();
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asm_inline volatile(
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" sacf 256\n"
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"0: cs %[old],%[new],%[uaddr]\n"
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"1: lhi %[rc],0\n"
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"2: sacf 768\n"
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EX_TABLE_UA_FAULT(0b, 2b, %[rc])
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EX_TABLE_UA_FAULT(1b, 2b, %[rc])
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: [rc] "=d" (rc), [old] "+d" (oldval), [uaddr] "+Q" (*uaddr)
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: [new] "d" (newval)
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: "cc", "memory");
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disable_sacf_uaccess(sacf_flag);
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*uval = oldval;
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instrument_copy_from_user_after(uval, uaddr, sizeof(*uval), 0);
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return rc;
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}
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#endif /* _ASM_S390_FUTEX_H */
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