On Mon, Mar 05, 2018 at 10:23:59AM -0800, Linus Torvalds 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. Right, as I said, up to v2 of this series I thought I could avoid the whole from-kernel-with-user-cr3 game, but that turned out to be wrong. Now I added the necessary check and handling for it, as at least the #DB handler needs it. > 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? Right, I will drop this patch. > > > 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". I put a selftest for that on my list of things to look into. I'll have no idea how difficult this will be, but I certainly find out :) Regards, Joerg -- 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>
