From mboxrd@z Thu Jan 1 00:00:00 1970 From: josh-iaAMLnmF4UmaiuxdJuQwMA@public.gmane.org Subject: Re: [PATCH 2/6] x86: Opt into HAVE_COPY_THREAD_TLS, for both 32-bit and 64-bit Date: Fri, 13 Mar 2015 15:43:19 -0700 Message-ID: <20150313224319.GA11282@cloud> References: <20150313223139.GD10954@cloud> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: Al Viro , Andrew Morton , Ingo Molnar , Kees Cook , Oleg Nesterov , "Paul E. McKenney" , "H. Peter Anvin" , Rik van Riel , Thomas Gleixner , Thiago Macieira , Michael Kerrisk , "linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org" , Linux API , Linux FS Devel , X86 ML To: Andy Lutomirski Return-path: Content-Disposition: inline In-Reply-To: Sender: linux-api-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org List-Id: linux-fsdevel.vger.kernel.org On Fri, Mar 13, 2015 at 03:38:31PM -0700, Andy Lutomirski wrote: > On Fri, Mar 13, 2015 at 3:31 PM, wrote: > > On Fri, Mar 13, 2015 at 03:01:16PM -0700, Andy Lutomirski wrote: > >> On Thu, Mar 12, 2015 at 6:40 PM, Josh Triplett wrote: > >> > For 32-bit userspace on a 64-bit kernel, this requires modifying > >> > stub32_clone to actually swap the appropriate arguments to match > >> > CONFIG_CLONE_BACKWARDS, rather than just leaving the C argument for tls > >> > broken. > >> > > >> > Signed-off-by: Josh Triplett > >> > Signed-off-by: Thiago Macieira > >> > --- > >> > arch/x86/Kconfig | 1 + > >> > arch/x86/ia32/ia32entry.S | 2 +- > >> > arch/x86/kernel/process_32.c | 6 +++--- > >> > arch/x86/kernel/process_64.c | 8 ++++---- > >> > 4 files changed, 9 insertions(+), 8 deletions(-) > >> > > >> > diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig > >> > index b7d31ca..4960b0d 100644 > >> > --- a/arch/x86/Kconfig > >> > +++ b/arch/x86/Kconfig > >> > @@ -124,6 +124,7 @@ config X86 > >> > select MODULES_USE_ELF_REL if X86_32 > >> > select MODULES_USE_ELF_RELA if X86_64 > >> > select CLONE_BACKWARDS if X86_32 > >> > + select HAVE_COPY_THREAD_TLS > >> > select ARCH_USE_BUILTIN_BSWAP > >> > select ARCH_USE_QUEUE_RWLOCK > >> > select OLD_SIGSUSPEND3 if X86_32 || IA32_EMULATION > >> > diff --git a/arch/x86/ia32/ia32entry.S b/arch/x86/ia32/ia32entry.S > >> > index 156ebca..0286735 100644 > >> > --- a/arch/x86/ia32/ia32entry.S > >> > +++ b/arch/x86/ia32/ia32entry.S > >> > @@ -487,7 +487,7 @@ GLOBAL(\label) > >> > ALIGN > >> > GLOBAL(stub32_clone) > >> > leaq sys_clone(%rip),%rax > >> > - mov %r8, %rcx > >> > + xchg %r8, %rcx > >> > jmp ia32_ptregs_common > >> > >> Do I understand correct that whatever function this is a stub for just > >> takes its arguments in the wrong order? If so, can we just fix it > >> instead of using xchg here? > > > > 32-bit x86 and 64-bit x86 take the arguments to clone in a different > > order, and stub32_clone fixes up the argument order then calls the > > 64-bit sys_clone. > > > > I'd love to see *all* the 32-on-64 compat stubs for clone rewritten in C > > under CONFIG_COMPAT. However, doing so would require encoding the > > knowledge for each 64-bit architecture for how its corresponding 32-bit > > architecture accepts arguments to clone, which is information that the > > current CONFIG_CLONE_BACKWARDS{1,2,3} don't include; it would then > > require cleaning up all the architecture-specific assembly stubs for > > 32-bit clone entry points. > > > > In the meantime, doing that *just* for 32-bit x86 on 64-bit x86 doesn't > > seem worth it, since it would require adding a new C entry point for > > compat_sys_clone under arch/x86 somewhere. > > > > One cleanup at a time. :) > > Fine w/ me. Thanks. > > > >> In general, I much prefer C code to new asm where it makes sense to > >> make this tradeoff. > > > > Agreed completely. However, this is at least conservation-of-asm, or > > reduction if you consider the pt_regs argument-grabbing hack to be > > asm-esque code. > > > >> Other than that, this is a huge improvement. You'll have minor > >> conflicts against -tip, though. > > > > Right, I've seen your current changes there. Should be a trivial merge > > though. > > > > Would you mind providing an ack for the series, or at least for the > > first two patches? > > I can give you an ok-in-principle on the first two. I'd need to stare > at the awful code for a bit to understand the @!*&! clone variants to > really ack them convincingly. I'd definitely appreciate the staring. :) > OTOH, it would be rather surprising if you messed it up in a way that > still boots on all three variants (native 32-bit, native 64-bit, and > compat). > > So, for the first two patches: > > Acked-by: Andy Lutomirski # assuming all bitnesses boot I did test all three, not just with booting but with a thread-local storage test. - Josh Triplett