On Tue, Oct 28, 2014 at 11:09:53AM -0700, Andy Lutomirski wrote: > On Tue, Oct 28, 2014 at 10:57 AM, Josh Triplett <[email protected]> wrote: > > On Tue, Oct 28, 2014 at 10:22:28AM -0700, Andy Lutomirski wrote: > >> This adds CONFIG_X86_VSYSCALL_EMULATION, guarded by CONFIG_EXPERT. > >> Turning it off completely disables vsyscall emulation, saving ~3.5k > >> for vsyscall_64.c, 4k for vsyscall_emu_64.S (the fake vsyscall > >> page), some tiny amount of core mm code that supports a gate area, > >> and possibly 4k for a wasted pagetable. The latter is because the > >> vsyscall addresses are misaligned and fit poorly in the fixmap. > >> > >> Signed-off-by: Andy Lutomirski <[email protected]> > > > > One minor nit below, but with or without that change, > > Reviewed-by: Josh Triplett <[email protected]> > > > >> --- a/arch/x86/xen/mmu.c > >> +++ b/arch/x86/xen/mmu.c > >> @@ -1456,11 +1456,13 @@ static int xen_pgd_alloc(struct mm_struct *mm) > >> user_pgd = (pgd_t *)__get_free_page(GFP_KERNEL | __GFP_ZERO); > >> page->private = (unsigned long)user_pgd; > >> > >> +#ifdef CONFIG_X86_VSYSCALL_EMULATION > >> if (user_pgd != NULL) { > >> user_pgd[pgd_index(VSYSCALL_ADDR)] = > >> __pgd(__pa(level3_user_vsyscall) | > >> _PAGE_TABLE); > >> ret = 0; > >> } > >> +#endif > > > > Could you instead make the if use IS_ENABLED? > > > > if (IS_ENABLED(CONFIG_X86_VSYSCALL_EMULATION) && user_pgd > > != NULL) > > > > That has the advantage of ensuring that the code continues to compile. > > (Given that you haven't removed level3_user_vsyscall, that should work.) > > I need the ret = 0, I think, so I'll resend. > > I think I'd rather use #ifdef here, since I think it would be great if > the Xen people could clean this up further. With this change, under > some configurations, there should be no user-accessible kernel > addresses at all. (Also, is there some PV mechanism > that I'm not thinking of that will break with this change? I know > I've tripped over Xen pagetable and fixmap oddities before.)
Not that I know of. The vsyscall is the only one that I know of that does this. Do you have a full patchset somewhere for testing? > > --Andy -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
