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linux-user/arm: Implement __kernel_cmpxchg with host atomics 

The existing implementation using start/end_exclusive
does not provide atomicity across processes.

Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
Message-Id: <20220323005839.94327-3-richard.henderson@linaro.org>
Signed-off-by: Laurent Vivier <laurent@vivier.eu>
This commit is contained in:
Richard Henderson 2022-03-22 17:58:38 -07:00 committed by Laurent Vivier
parent 6e05e7047c
commit 7f4f0d9ea8
1 changed files with 62 additions and 25 deletions
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87
linux-user/arm/cpu_loop.c
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@ -75,7 +75,67 @@
put_user_u16(__x, (gaddr)); \
})
/* Commpage handling -- there is no commpage for AArch64 */
/*
* Similar to code in accel/tcg/user-exec.c, but outside the execution loop.
* Must be called with mmap_lock.
* 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.
*/
static void *atomic_mmu_lookup(CPUArchState *env, uint32_t addr, int size)
{
int need_flags = PAGE_READ | PAGE_WRITE_ORG | PAGE_VALID;
int page_flags;
/* Enforce guest required alignment. */
if (unlikely(addr & (size - 1))) {
force_sig_fault(TARGET_SIGBUS, TARGET_BUS_ADRALN, addr);
return NULL;
}
page_flags = page_get_flags(addr);
if (unlikely((page_flags & need_flags) != need_flags)) {
force_sig_fault(TARGET_SIGSEGV,
page_flags & PAGE_VALID ?
TARGET_SEGV_ACCERR : TARGET_SEGV_MAPERR, addr);
return NULL;
}
return g2h(env_cpu(env), addr);
}
/*
* See the Linux kernel's Documentation/arm/kernel_user_helpers.rst
* Input:
* r0 = oldval
* r1 = newval
* r2 = pointer to target value
*
* Output:
* r0 = 0 if *ptr was changed, non-0 if no exchange happened
* C set if *ptr was changed, clear if no exchange happened
*/
static void arm_kernel_cmpxchg32_helper(CPUARMState *env)
{
uint32_t oldval, newval, val, addr, cpsr, *host_addr;
oldval = env->regs[0];
newval = env->regs[1];
addr = env->regs[2];
mmap_lock();
host_addr = atomic_mmu_lookup(env, addr, 4);
if (!host_addr) {
mmap_unlock();
return;
}
val = qatomic_cmpxchg__nocheck(host_addr, oldval, newval);
mmap_unlock();
cpsr = (val == oldval) * CPSR_C;
cpsr_write(env, cpsr, CPSR_C, CPSRWriteByInstr);
env->regs[0] = cpsr ? 0 : -1;
}
/*
* See the Linux kernel's Documentation/arm/kernel_user_helpers.txt
@ -153,36 +213,13 @@ static int
do_kernel_trap(CPUARMState *env)
{
uint32_t addr;
uint32_t cpsr;
uint32_t val;
switch (env->regs[15]) {
case 0xffff0fa0: /* __kernel_memory_barrier */
smp_mb();
break;
case 0xffff0fc0: /* __kernel_cmpxchg */
/* 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[2];
/* FIXME: This should SEGV if the access fails. */
if (get_user_u32(val, addr))
val = ~env->regs[0];
if (val == env->regs[0]) {
val = env->regs[1];
/* FIXME: Check for segfaults. */
put_user_u32(val, addr);
env->regs[0] = 0;
cpsr |= CPSR_C;
} else {
env->regs[0] = -1;
cpsr &= ~CPSR_C;
}
cpsr_write(env, cpsr, CPSR_C, CPSRWriteByInstr);
end_exclusive();
arm_kernel_cmpxchg32_helper(env);
break;
case 0xffff0fe0: /* __kernel_get_tls */
env->regs[0] = cpu_get_tls(env);