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accel/tcg: Split out handle_sigsegv_accerr_write

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This is the major portion of handle_cpu_signal which is specific
to tcg, handling the page protections for the translations.
Most of the rest will migrate to linux-user/ shortly.

Reviewed-by: Warner Losh <imp@bsdimp.com>
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
---
v2: Pass guest address to handle_sigsegv_accerr_write.
This commit is contained in:
Richard Henderson 2021-09-12 19:47:29 -07:00
parent f920ffdd8e
commit 5e38ba7dde
2 changed files with 72 additions and 41 deletions
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101
accel/tcg/user-exec.c
View file

@ -114,6 +114,52 @@ MMUAccessType adjust_signal_pc(uintptr_t *pc, bool is_write)
return is_write ? MMU_DATA_STORE : MMU_DATA_LOAD;
}
/**
* handle_sigsegv_accerr_write:
* @cpu: the cpu context
* @old_set: the sigset_t from the signal ucontext_t
* @host_pc: the host pc, adjusted for the signal
* @guest_addr: the guest address of the fault
*
* Return true if the write fault has been handled, and should be re-tried.
*
* Note that it is important that we don't call page_unprotect() unless
* this is really a "write to nonwriteable page" fault, because
* page_unprotect() assumes that if it is called for an access to
* a page that's writeable this means we had two threads racing and
* another thread got there first and already made the page writeable;
* so we will retry the access. If we were to call page_unprotect()
* for some other kind of fault that should really be passed to the
* guest, we'd end up in an infinite loop of retrying the faulting access.
*/
bool handle_sigsegv_accerr_write(CPUState *cpu, sigset_t *old_set,
uintptr_t host_pc, abi_ptr guest_addr)
{
switch (page_unprotect(guest_addr, host_pc)) {
case 0:
/*
* Fault not caused by a page marked unwritable to protect
* cached translations, must be the guest binary's problem.
*/
return false;
case 1:
/*
* Fault caused by protection of cached translation; TBs
* invalidated, so resume execution.
*/
return true;
case 2:
/*
* Fault caused by protection of cached translation, and the
* currently executing TB was modified and must be exited immediately.
*/
cpu_exit_tb_from_sighandler(cpu, old_set);
/* NORETURN */
default:
g_assert_not_reached();
}
}
/*
* 'pc' is the host PC at which the exception was raised.
* 'address' is the effective address of the memory exception.
@ -125,8 +171,9 @@ static inline int handle_cpu_signal(uintptr_t pc, siginfo_t *info,
{
CPUState *cpu = current_cpu;
CPUClass *cc;
unsigned long address = (unsigned long)info->si_addr;
unsigned long host_addr = (unsigned long)info->si_addr;
MMUAccessType access_type = adjust_signal_pc(&pc, is_write);
abi_ptr guest_addr;
/* For synchronous signals we expect to be coming from the vCPU
* thread (so current_cpu should be valid) and either from running
@ -143,49 +190,21 @@ static inline int handle_cpu_signal(uintptr_t pc, siginfo_t *info,
#if defined(DEBUG_SIGNAL)
printf("qemu: SIGSEGV pc=0x%08lx address=%08lx w=%d oldset=0x%08lx\n",
pc, address, is_write, *(unsigned long *)old_set);
pc, host_addr, is_write, *(unsigned long *)old_set);
#endif
/* XXX: locking issue */
/* Note that it is important that we don't call page_unprotect() unless
* this is really a "write to nonwriteable page" fault, because
* page_unprotect() assumes that if it is called for an access to
* a page that's writeable this means we had two threads racing and
* another thread got there first and already made the page writeable;
* so we will retry the access. If we were to call page_unprotect()
* for some other kind of fault that should really be passed to the
* guest, we'd end up in an infinite loop of retrying the faulting
* access.
*/
if (is_write && info->si_signo == SIGSEGV && info->si_code == SEGV_ACCERR &&
h2g_valid(address)) {
switch (page_unprotect(h2g(address), pc)) {
case 0:
/* Fault not caused by a page marked unwritable to protect
* cached translations, must be the guest binary's problem.
*/
break;
case 1:
/* Fault caused by protection of cached translation; TBs
* invalidated, so resume execution. Retain helper_retaddr
* for a possible second fault.
*/
return 1;
case 2:
/* Fault caused by protection of cached translation, and the
* currently executing TB was modified and must be exited
* immediately. Clear helper_retaddr for next execution.
*/
cpu_exit_tb_from_sighandler(cpu, old_set);
/* NORETURN */
default:
g_assert_not_reached();
}
}
/* Convert forcefully to guest address space, invalid addresses
are still valid segv ones */
address = h2g_nocheck(address);
guest_addr = h2g_nocheck(host_addr);
/* XXX: locking issue */
if (is_write &&
info->si_signo == SIGSEGV &&
info->si_code == SEGV_ACCERR &&
h2g_valid(host_addr) &&
handle_sigsegv_accerr_write(cpu, old_set, pc, guest_addr)) {
return 1;
}
/*
* There is no way the target can handle this other than raising
@ -194,7 +213,7 @@ static inline int handle_cpu_signal(uintptr_t pc, siginfo_t *info,
sigprocmask(SIG_SETMASK, old_set, NULL);
cc = CPU_GET_CLASS(cpu);
cc->tcg_ops->tlb_fill(cpu, address, 0, access_type,
cc->tcg_ops->tlb_fill(cpu, guest_addr, 0, access_type,
MMU_USER_IDX, false, pc);
g_assert_not_reached();
}

12
include/exec/exec-all.h
View file

@ -673,6 +673,18 @@ static inline tb_page_addr_t get_page_addr_code_hostp(CPUArchState *env,
*/
MMUAccessType adjust_signal_pc(uintptr_t *pc, bool is_write);
/**
* handle_sigsegv_accerr_write:
* @cpu: the cpu context
* @old_set: the sigset_t from the signal ucontext_t
* @host_pc: the host pc, adjusted for the signal
* @host_addr: the host address of the fault
*
* Return true if the write fault has been handled, and should be re-tried.
*/
bool handle_sigsegv_accerr_write(CPUState *cpu, sigset_t *old_set,
uintptr_t host_pc, abi_ptr guest_addr);
/**
* cpu_signal_handler
* @signum: host signal number