On Tue, Jan 30, 2024 at 06:57:24PM +0800, Tong Tiangen wrote:
> 在 2024/1/30 1:51, Mark Rutland 写道:
> > On Mon, Jan 29, 2024 at 09:46:48PM +0800, Tong Tiangen wrote:
> > > diff --git a/arch/arm64/mm/fault.c b/arch/arm64/mm/fault.c
> > > index 55f6455a8284..312932dc100b 100644
> > > --- a/arch/arm64/mm/fault.c
> > > +++ b/arch/arm64/mm/fault.c
> > > @@ -730,6 +730,31 @@ static int do_bad(unsigned long far, unsigned long esr, struct pt_regs *regs)
> > > return 1; /* "fault" */
> > > }
> > > +static bool arm64_do_kernel_sea(unsigned long addr, unsigned int esr,
> > > + struct pt_regs *regs, int sig, int code)
> > > +{
> > > + if (!IS_ENABLED(CONFIG_ARCH_HAS_COPY_MC))
> > > + return false;
> > > +
> > > + if (user_mode(regs))
> > > + return false;
> >
> > This function is called "arm64_do_kernel_sea"; surely the caller should *never*
> > call this for a SEA taken from user mode?
>
> In do_sea(), the processing logic is as follows:
> do_sea()
> {
> [...]
> if (user_mode(regs) && apei_claim_sea(regs) == 0) {
> return 0;
> }
> [...]
> //[1]
> if (!arm64_do_kernel_sea()) {
> arm64_notify_die();
> }
> }
>
> [1] user_mode() is still possible to go here,If user_mode() goes here,
> it indicates that the impact caused by the memory error cannot be
> processed correctly by apei_claim_sea().
>
>
> In this case, only arm64_notify_die() can be used, This also maintains
> the original logic of user_mode()'s processing.
My point is that either:
(a) The name means that this should *only* be called for SEAs from a kernel
context, and the caller should be responsible for ensuring that.
(b) The name is misleading, and the 'kernel' part should be removed from the
name.
I prefer (a), and if you head down that route it's clear that you can get rid
of a bunch of redundant logic and remove the need for do_kernel_sea(), anyway,
e.g.
| static int do_sea(unsigned long far, unsigned long esr, struct pt_regs *regs)
| {
| const struct fault_info *inf = esr_to_fault_info(esr);
| bool claimed = apei_claim_sea(regs) == 0;
| unsigned long siaddr;
|
| if (claimed) {
| if (user_mode(regs)) {
| /*
| * APEI claimed this as a firmware-first notification.
| * Some processing deferred to task_work before ret_to_user().
| */
| return 0;
| } else {
| /*
| * TODO: explain why this is correct.
| */
| if ((current->flags & PF_KTHREAD) &&
| fixup_exception_mc(regs))
| return 0;
| }
| }
|
| if (esr & ESR_ELx_FnV) {
| siaddr = 0;
| } else {
| /*
| * The architecture specifies that the tag bits of FAR_EL1 are
| * UNKNOWN for synchronous external aborts. Mask them out now
| * so that userspace doesn't see them.
| */
| siaddr = untagged_addr(far);
| }
| arm64_notify_die(inf->name, regs, inf->sig, inf->code, siaddr, esr);
|
| return 0;
| }
> > > +
> > > + if (apei_claim_sea(regs) < 0)
> > > + return false;
> > > +
> > > + if (!fixup_exception_mc(regs))
> > > + return false;
> > > +
> > > + if (current->flags & PF_KTHREAD)
> > > + return true;
> >
> > I think this needs a comment; why do we allow kthreads to go on, yet kill user
> > threads? What about helper threads (e.g. for io_uring)?
>
> If a memroy error occurs in the kernel thread, the problem is more
> serious than that of the user thread. As a result, related kernel
> functions, such as khugepaged, cannot run properly. kernel panic should
> be a better choice at this time.
>
> Therefore, the processing scope of this framework is limited to the user
> thread.
That's reasonable, but needs to be explained in a comment.
Also, as above, I think you haven't conisderd helper threads (e.g. io_uring),
which don't have PF_KTHREAD set but do have PF_USER_WORKER set. I suspect those
need the same treatment as kthreads.
> > > + set_thread_esr(0, esr);
> >
> > Why do we set the ESR to 0?
>
> The purpose is to reuse the logic of arm64_notify_die() and set the
> following parameters before sending signals to users:
> current->thread.fault_address = 0;
> current->thread.fault_code = err;
Ok, but there's no need to open-code that.
As per my above example, please continue to use the existing call to
arm64_notify_die() rather than open-coding bits of it.
Mark.
