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linux-user/arm: Implement __kernel_cmpxchg64 with host atomics 

If CONFIG_ATOMIC64, we can use a host cmpxchg and provide
atomicity across processes; otherwise we have no choice but
to continue using start/end_exclusive.

Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
Message-Id: <20220323005839.94327-4-richard.henderson@linaro.org>
Signed-off-by: Laurent Vivier <laurent@vivier.eu>
This commit is contained in:
Richard Henderson 2022-03-22 17:58:39 -07:00 committed by Laurent Vivier
parent 7f4f0d9ea8
commit 330ea9d1d8
1 changed files with 38 additions and 41 deletions
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79
linux-user/arm/cpu_loop.c
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@ -138,7 +138,7 @@ static void arm_kernel_cmpxchg32_helper(CPUARMState *env)
}
/*
* See the Linux kernel's Documentation/arm/kernel_user_helpers.txt
* See the Linux kernel's Documentation/arm/kernel_user_helpers.rst
* Input:
* r0 = pointer to oldval
* r1 = pointer to newval
@ -155,57 +155,54 @@ static void arm_kernel_cmpxchg64_helper(CPUARMState *env)
{
uint64_t oldval, newval, val;
uint32_t addr, cpsr;
uint64_t *host_addr;
/* Based on the 32 bit code in do_kernel_trap */
addr = env->regs[0];
if (get_user_u64(oldval, addr)) {
goto segv;
}
/* XXX: This only works between threads, not between processes.
It's probably possible to implement this with native host
operations. However things like ldrex/strex are much harder so
there's not much point trying. */
start_exclusive();
cpsr = cpsr_read(env);
addr = env->regs[1];
if (get_user_u64(newval, addr)) {
goto segv;
}
mmap_lock();
addr = env->regs[2];
if (get_user_u64(oldval, env->regs[0])) {
env->exception.vaddress = env->regs[0];
goto segv;
};
if (get_user_u64(newval, env->regs[1])) {
env->exception.vaddress = env->regs[1];
goto segv;
};
if (get_user_u64(val, addr)) {
env->exception.vaddress = addr;
goto segv;
host_addr = atomic_mmu_lookup(env, addr, 8);
if (!host_addr) {
mmap_unlock();
return;
}
#ifdef CONFIG_ATOMIC64
val = qatomic_cmpxchg__nocheck(host_addr, oldval, newval);
cpsr = (val == oldval) * CPSR_C;
#else
/*
* This only works between threads, not between processes, but since
* the host has no 64-bit cmpxchg, it is the best that we can do.
*/
start_exclusive();
val = *host_addr;
if (val == oldval) {
val = newval;
if (put_user_u64(val, addr)) {
env->exception.vaddress = addr;
goto segv;
};
env->regs[0] = 0;
cpsr |= CPSR_C;
*host_addr = newval;
cpsr = CPSR_C;
} else {
env->regs[0] = -1;
cpsr &= ~CPSR_C;
cpsr = 0;
}
cpsr_write(env, cpsr, CPSR_C, CPSRWriteByInstr);
end_exclusive();
#endif
mmap_unlock();
cpsr_write(env, cpsr, CPSR_C, CPSRWriteByInstr);
env->regs[0] = cpsr ? 0 : -1;
return;
segv:
end_exclusive();
/* We get the PC of the entry address - which is as good as anything,
on a real kernel what you get depends on which mode it uses. */
/* XXX: check env->error_code */
force_sig_fault(TARGET_SIGSEGV, TARGET_SEGV_MAPERR,
env->exception.vaddress);
segv:
force_sig_fault(TARGET_SIGSEGV,
page_get_flags(addr) & PAGE_VALID ?
TARGET_SEGV_ACCERR : TARGET_SEGV_MAPERR, addr);
}
/* Handle a jump to the kernel code page. */