accel/tcg: Split out handle_sigsegv_accerr_write

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.

accel/tcg/user-exec.c

@@ -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();
 }

include/exec/exec-all.h

@@ -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