mirror of
https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git
synced 2024-08-26 02:39:48 +00:00
s390: Clarify pagefault interrupt
While looking at set_task_state() users I stumbled over the s390 pfault interrupt code. Since Heiko provided a great explanation on how it worked, I figured we ought to preserve this. Also make a few little tweaks to the code to aid in readability and explicitly comment the unusual blocking scheme. Based-on-text-by: Heiko Carstens <heiko.carstens@de.ibm.com> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com> Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
This commit is contained in:
parent
5a3b7b1128
commit
0227f7c42d
1 changed files with 33 additions and 8 deletions
|
@ -631,6 +631,29 @@ void pfault_fini(void)
|
|||
static DEFINE_SPINLOCK(pfault_lock);
|
||||
static LIST_HEAD(pfault_list);
|
||||
|
||||
#define PF_COMPLETE 0x0080
|
||||
|
||||
/*
|
||||
* The mechanism of our pfault code: if Linux is running as guest, runs a user
|
||||
* space process and the user space process accesses a page that the host has
|
||||
* paged out we get a pfault interrupt.
|
||||
*
|
||||
* This allows us, within the guest, to schedule a different process. Without
|
||||
* this mechanism the host would have to suspend the whole virtual cpu until
|
||||
* the page has been paged in.
|
||||
*
|
||||
* So when we get such an interrupt then we set the state of the current task
|
||||
* to uninterruptible and also set the need_resched flag. Both happens within
|
||||
* interrupt context(!). If we later on want to return to user space we
|
||||
* recognize the need_resched flag and then call schedule(). It's not very
|
||||
* obvious how this works...
|
||||
*
|
||||
* Of course we have a lot of additional fun with the completion interrupt (->
|
||||
* host signals that a page of a process has been paged in and the process can
|
||||
* continue to run). This interrupt can arrive on any cpu and, since we have
|
||||
* virtual cpus, actually appear before the interrupt that signals that a page
|
||||
* is missing.
|
||||
*/
|
||||
static void pfault_interrupt(struct ext_code ext_code,
|
||||
unsigned int param32, unsigned long param64)
|
||||
{
|
||||
|
@ -639,10 +662,9 @@ static void pfault_interrupt(struct ext_code ext_code,
|
|||
pid_t pid;
|
||||
|
||||
/*
|
||||
* Get the external interruption subcode & pfault
|
||||
* initial/completion signal bit. VM stores this
|
||||
* in the 'cpu address' field associated with the
|
||||
* external interrupt.
|
||||
* Get the external interruption subcode & pfault initial/completion
|
||||
* signal bit. VM stores this in the 'cpu address' field associated
|
||||
* with the external interrupt.
|
||||
*/
|
||||
subcode = ext_code.subcode;
|
||||
if ((subcode & 0xff00) != __SUBCODE_MASK)
|
||||
|
@ -658,7 +680,7 @@ static void pfault_interrupt(struct ext_code ext_code,
|
|||
if (!tsk)
|
||||
return;
|
||||
spin_lock(&pfault_lock);
|
||||
if (subcode & 0x0080) {
|
||||
if (subcode & PF_COMPLETE) {
|
||||
/* signal bit is set -> a page has been swapped in by VM */
|
||||
if (tsk->thread.pfault_wait == 1) {
|
||||
/* Initial interrupt was faster than the completion
|
||||
|
@ -687,8 +709,7 @@ static void pfault_interrupt(struct ext_code ext_code,
|
|||
goto out;
|
||||
if (tsk->thread.pfault_wait == 1) {
|
||||
/* Already on the list with a reference: put to sleep */
|
||||
__set_task_state(tsk, TASK_UNINTERRUPTIBLE);
|
||||
set_tsk_need_resched(tsk);
|
||||
goto block;
|
||||
} else if (tsk->thread.pfault_wait == -1) {
|
||||
/* Completion interrupt was faster than the initial
|
||||
* interrupt (pfault_wait == -1). Set pfault_wait
|
||||
|
@ -703,7 +724,11 @@ static void pfault_interrupt(struct ext_code ext_code,
|
|||
get_task_struct(tsk);
|
||||
tsk->thread.pfault_wait = 1;
|
||||
list_add(&tsk->thread.list, &pfault_list);
|
||||
__set_task_state(tsk, TASK_UNINTERRUPTIBLE);
|
||||
block:
|
||||
/* Since this must be a userspace fault, there
|
||||
* is no kernel task state to trample. Rely on the
|
||||
* return to userspace schedule() to block. */
|
||||
__set_current_state(TASK_UNINTERRUPTIBLE);
|
||||
set_tsk_need_resched(tsk);
|
||||
}
|
||||
}
|
||||
|
|
Loading…
Reference in a new issue