[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [Xen-devel] [PATCH 3/3] x86_64, vsyscall: Make vsyscall emulation configurable
On Dec 1, 2014 2:08 PM, "Konrad Rzeszutek Wilk" <konrad.wilk@xxxxxxxxxx> wrote: > > On Wed, Oct 29, 2014 at 02:30:29PM -0700, Andy Lutomirski wrote: > > On Oct 29, 2014 1:00 PM, "Konrad Rzeszutek Wilk" <konrad.wilk@xxxxxxxxxx> > > wrote: > > > > > > On Tue, Oct 28, 2014 at 11:09:53AM -0700, Andy Lutomirski wrote: > > > > On Tue, Oct 28, 2014 at 10:57 AM, Josh Triplett <josh@xxxxxxxxxxxxxxxx> > > > > 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 <luto@xxxxxxxxxxxxxx> > > > > > > > > > > One minor nit below, but with or without that change, > > > > > Reviewed-by: Josh Triplett <josh@xxxxxxxxxxxxxxxx> > > > > > > > > > >> --- 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 > > What about the vsyscall time stamp (aka kvm-clock). That is not > really VSYSCALL emulation based but normal code? That's entirely separate now. > > > > > 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. > > > > There's kvm-clock, too, but that may never co-exist with Xen. > > It will eventually. Hmm. Maybe I should clean up the read code first. --Andy > > > > I tagged v2 here: > > > > https://git.kernel.org/cgit/linux/kernel/git/luto/linux.git/tag/?id=optional-vsyscall-emulation-v2 > > > > and I'll send it out in a bit. > > > > --Andy > > > > > > > > Do you have a full patchset somewhere for testing? > > > > > > > > --Andy _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxx http://lists.xen.org/xen-devel
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