On Mon, Mar 5, 2018 at 1:23 PM, Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx> wrote: > On Mon, Mar 5, 2018 at 5:12 AM, Joerg Roedel <joro@xxxxxxxxxx> wrote: >> >>> The things is, we *know* that we will restore two segment registers with the >>> user cr3 already loaded: CS and SS get restored with the final iret. >> >> Yeah, I know, but the iret-exception path is fine because it will >> deliver a SIGILL and doesn't return to the faulting iret. > > That's not so much my worry, as just getting %cr3 wrong. The fact is, > we still take the exception, and we still have to handle it, and that > still needs to get the user<->kernel cr3 right. > > So then the whole "restore segments early" must be wrong, because > *that* path must get it all right too, no? > > And it appears that the code *does* get it right, and you can just > avoid this patch entirely? > >> The iret-exception case is tested by the ldt_gdt selftest (the >> do_multicpu_tests subtest). But I didn't actually tested single-stepping >> through sysenter yet. I just re-ran the same tests I did with v2 on this >> patch-set. > > Ok. Maybe we should have a test for the "take DB on first instruction > of sysenter". > > Linus There already is a test: single_step_syscall.c -- Brian Gerst -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>
