[PATCH v1 07/21] target/i386: add BQL to do_interrupt and cpu_exec_interrupt

[Robert Foley]

This is part of a series of changes to remove the implied BQL
from the common code of cpu_handle_interrupt and
cpu_handle_exception.  As part of removing the implied BQL
from the common code, we are pushing the BQL holding
down into the per-arch implementation functions of
do_interrupt and cpu_exec_interrupt.

The purpose of this set of changes is to set the groundwork
so that an arch could move towards removing
the BQL from the cpu_handle_interrupt/exception paths.

This approach was suggested by Paolo Bonzini.
For reference, here are two key posts in the discussion, explaining
the reasoning/benefits of this approach.
https://lists.gnu.org/archive/html/qemu-devel/2020-07/msg08731.html
https://lists.gnu.org/archive/html/qemu-devel/2020-08/msg00044.html

Signed-off-by: Robert Foley <robert.foley@linaro.org>
---
 target/i386/seg_helper.c | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/target/i386/seg_helper.c b/target/i386/seg_helper.c
index 818f65f35f..114d4a0d24 100644
--- a/target/i386/seg_helper.c
+++ b/target/i386/seg_helper.c
@@ -1284,7 +1284,7 @@ void x86_cpu_do_interrupt(CPUState *cs)
 {
     X86CPU *cpu = X86_CPU(cs);
     CPUX86State *env = &cpu->env;
-
+    qemu_mutex_lock_iothread();
 #if defined(CONFIG_USER_ONLY)
     /* if user mode only, we simulate a fake exception
        which will be handled outside the cpu execution
@@ -1308,6 +1308,7 @@ void x86_cpu_do_interrupt(CPUState *cs)
         env->old_exception = -1;
     }
 #endif
+    qemu_mutex_unlock_iothread();
 }
 
 void do_interrupt_x86_hardirq(CPUX86State *env, int intno, int is_hw)
@@ -1320,9 +1321,10 @@ bool x86_cpu_exec_interrupt(CPUState *cs, int 
interrupt_request)
     X86CPU *cpu = X86_CPU(cs);
     CPUX86State *env = &cpu->env;
     int intno;
-
+    qemu_mutex_lock_iothread();
     interrupt_request = x86_cpu_pending_interrupt(cs, interrupt_request);
     if (!interrupt_request) {
+        qemu_mutex_unlock_iothread();
         return false;
     }
 
@@ -1377,6 +1379,7 @@ bool x86_cpu_exec_interrupt(CPUState *cs, int 
interrupt_request)
     }
 
     /* Ensure that no TB jump will be modified as the program flow was 
changed.  */
+    qemu_mutex_unlock_iothread();
     return true;
 }
 
-- 
2.17.1