[RFC v3 08/19] arch: um: add shim to trap to allow installing a fault catcher for tests

brendanhiggins
2018-12-03T23:34:57Z

On Thu, Nov 29, 2018 at 7:34 PM Luis Chamberlain <mcgrof at kernel.org> wrote:
>
> On Wed, Nov 28, 2018 at 11:36:25AM -0800, Brendan Higgins wrote:
> > diff --git a/arch/um/kernel/trap.c b/arch/um/kernel/trap.c
> > index cced829460427..bf90e678b3d71 100644
> > --- a/arch/um/kernel/trap.c
> > +++ b/arch/um/kernel/trap.c
> > @@ -201,6 +201,12 @@ void segv_handler(int sig, struct siginfo *unused_si, struct uml_pt_regs *regs)
> > segv(*fi, UPT_IP(regs), UPT_IS_USER(regs), regs);
> > }
> >
> > +static void segv_run_catcher(jmp_buf *catcher, void *fault_addr)
> > +{
> > + current->thread.fault_addr = fault_addr;
> > + UML_LONGJMP(catcher, 1);
> > +}
> > +
> > /*
> > * We give a *copy* of the faultinfo in the regs to segv.
> > * This must be done, since nesting SEGVs could overwrite
> > @@ -219,7 +225,10 @@ unsigned long segv(struct faultinfo fi, unsigned long ip, int is_user,
> > if (!is_user && regs)
> > current->thread.segv_regs = container_of(regs, struct pt_regs, regs);
> >
> > - if (!is_user && (address >= start_vm) && (address < end_vm)) {
> > + catcher = current->thread.fault_catcher;
>
> This and..
>
> > + if (catcher && current->thread.is_running_test)
> > + segv_run_catcher(catcher, (void *) address);
> > + else if (!is_user && (address >= start_vm) && (address < end_vm)) {
> > flush_tlb_kernel_vm();
> > goto out;
> > }
>
> *not this*

I don't understand. Are you saying the previous block of code is good
and this one is bad?

>
> > @@ -246,12 +255,10 @@ unsigned long segv(struct faultinfo fi, unsigned long ip, int is_user,
> > address = 0;
> > }
> >
> > - catcher = current->thread.fault_catcher;
> > if (!err)
> > goto out;
> > else if (catcher != NULL) {
> > - current->thread.fault_addr = (void *) address;
> > - UML_LONGJMP(catcher, 1);
> > + segv_run_catcher(catcher, (void *) address);
> > }
> > else if (current->thread.fault_addr != NULL)
> > panic("fault_addr set but no fault catcher");
>
> But with this seems one atomic change which should be submitted
> separately, its just a helper. Think it would make the actual
> change needed easier to review, ie, your needed changes would
> be smaller and clearer for what you need.

Are you suggesting that I pull out the bits needed to implement abort
in the next patch and squash it into this one?