Commit 921ebd8f authored by Andrew Waterman's avatar Andrew Waterman Committed by Palmer Dabbelt

RISC-V: Allow userspace to flush the instruction cache

Despite RISC-V having a direct 'fence.i' instruction available to
userspace (which we can't trap!), that's not actually viable when
running on Linux because the kernel might schedule a process on another
hart.  There is no way for userspace to handle this without invoking the
kernel (as it doesn't know the thread->hart mappings), so we've defined
a RISC-V specific system call to flush the instruction cache.

This patch adds both a system call and a VDSO entry.  If possible, we'd
like to avoid having the system call be considered part of the
user-facing ABI and instead restrict that to the VDSO entry -- both just
in general to avoid having additional user-visible ABI to maintain, and
because we'd prefer that users just call the VDSO entry because there
might be a better way to do this in the future (ie, one that doesn't
require entering the kernel).
Signed-off-by: 's avatarAndrew Waterman <andrew@sifive.com>
Signed-off-by: 's avatarPalmer Dabbelt <palmer@sifive.com>
parent 08f051ed
......@@ -52,4 +52,10 @@ void flush_icache_mm(struct mm_struct *mm, bool local);
#endif /* CONFIG_SMP */
/*
* Bits in sys_riscv_flush_icache()'s flags argument.
*/
#define SYS_RISCV_FLUSH_ICACHE_LOCAL 1UL
#define SYS_RISCV_FLUSH_ICACHE_ALL (SYS_RISCV_FLUSH_ICACHE_LOCAL)
#endif /* _ASM_RISCV_CACHEFLUSH_H */
/*
* Copyright (C) 2017 SiFive
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License version 2 as
* published by the Free Software Foundation.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program. If not, see <http://www.gnu.org/licenses/>.
*/
#ifndef _ASM_RISCV_VDSO_SYSCALLS_H
#define _ASM_RISCV_VDSO_SYSCALLS_H
#ifdef CONFIG_SMP
/* These syscalls are only used by the vDSO and are not in the uapi. */
#define __NR_riscv_flush_icache (__NR_arch_specific_syscall + 15)
__SYSCALL(__NR_riscv_flush_icache, sys_riscv_flush_icache)
#endif
#endif /* _ASM_RISCV_VDSO_H */
......@@ -38,4 +38,8 @@ struct vdso_data {
(void __user *)((unsigned long)(base) + __vdso_##name); \
})
#ifdef CONFIG_SMP
asmlinkage long sys_riscv_flush_icache(uintptr_t, uintptr_t, uintptr_t);
#endif
#endif /* _ASM_RISCV_VDSO_H */
......@@ -16,6 +16,7 @@
#include <linux/syscalls.h>
#include <asm/cmpxchg.h>
#include <asm/unistd.h>
#include <asm/cacheflush.h>
static long riscv_sys_mmap(unsigned long addr, unsigned long len,
unsigned long prot, unsigned long flags,
......@@ -47,3 +48,34 @@ SYSCALL_DEFINE6(mmap2, unsigned long, addr, unsigned long, len,
return riscv_sys_mmap(addr, len, prot, flags, fd, offset, 12);
}
#endif /* !CONFIG_64BIT */
#ifdef CONFIG_SMP
/*
* Allows the instruction cache to be flushed from userspace. Despite RISC-V
* having a direct 'fence.i' instruction available to userspace (which we
* can't trap!), that's not actually viable when running on Linux because the
* kernel might schedule a process on another hart. There is no way for
* userspace to handle this without invoking the kernel (as it doesn't know the
* thread->hart mappings), so we've defined a RISC-V specific system call to
* flush the instruction cache.
*
* sys_riscv_flush_icache() is defined to flush the instruction cache over an
* address range, with the flush applying to either all threads or just the
* caller. We don't currently do anything with the address range, that's just
* in there for forwards compatibility.
*/
SYSCALL_DEFINE3(riscv_flush_icache, uintptr_t, start, uintptr_t, end,
uintptr_t, flags)
{
struct mm_struct *mm = current->mm;
bool local = (flags & SYS_RISCV_FLUSH_ICACHE_LOCAL) != 0;
/* Check the reserved flags. */
if (unlikely(flags & !SYS_RISCV_FLUSH_ICACHE_ALL))
return -EINVAL;
flush_icache_mm(mm, local);
return 0;
}
#endif
......@@ -15,6 +15,7 @@
#include <linux/linkage.h>
#include <linux/syscalls.h>
#include <asm-generic/syscalls.h>
#include <asm/vdso.h>
#undef __SYSCALL
#define __SYSCALL(nr, call) [nr] = (call),
......@@ -22,4 +23,5 @@
void *sys_call_table[__NR_syscalls] = {
[0 ... __NR_syscalls - 1] = sys_ni_syscall,
#include <asm/unistd.h>
#include <asm/vdso-syscalls.h>
};
......@@ -6,6 +6,7 @@ vdso-syms += gettimeofday
vdso-syms += clock_gettime
vdso-syms += clock_getres
vdso-syms += getcpu
vdso-syms += flush_icache
# Files to link into the vdso
obj-vdso = $(patsubst %, %.o, $(vdso-syms))
......
/*
* Copyright (C) 2017 SiFive
*
* This program is free software; you can redistribute it and/or
* modify it under the terms of the GNU General Public License
* as published by the Free Software Foundation, version 2.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*/
#include <linux/linkage.h>
#include <asm/unistd.h>
#include <asm/vdso-syscalls.h>
.text
/* int __vdso_flush_icache(void *start, void *end, unsigned long flags); */
ENTRY(__vdso_flush_icache)
.cfi_startproc
#ifdef CONFIG_SMP
li a7, __NR_riscv_flush_icache
ecall
#else
fence.i
li a0, 0
#endif
ret
.cfi_endproc
ENDPROC(__vdso_flush_icache)
......@@ -74,6 +74,7 @@ VERSION
__vdso_clock_gettime;
__vdso_clock_getres;
__vdso_getcpu;
__vdso_flush_icache;
local: *;
};
}
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