| Message ID | 20181220202518.21442-4-sean.j.christopherson@intel.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | KVM: VMX: Clean up VM-Enter/VM-Exit asm code | expand |
Hi Sean, On Thu, Dec 20, 2018 at 9:25 PM Sean Christopherson <sean.j.christopherson@intel.com> wrote: > > The -ftracer optimization was disabled in __noclone as a workaround to > GCC duplicating a blob of inline assembly that happened to define a > global variable. It has been pointed out that no amount of workarounds > can guarantee the compiler won't duplicate inline assembly[1], and that > disabling the -ftracer optimization has several unintended and nasty > side effects[2][3]. > > Now that the offending KVM code which required the workaround has > been properly fixed and no longer uses __noclone, remove the -ftracer > optimization tweak from __noclone. > > [1] https://lore.kernel.org/lkml/ri6y38lo23g.fsf@suse.cz/T/#u > [2] https://lore.kernel.org/lkml/20181218140105.ajuiglkpvstt3qxs@treble/T/#u > [3] https://patchwork.kernel.org/patch/8707981/#21817015 > > This reverts commit 95272c29378ee7dc15f43fa2758cb28a5913a06d. > > Suggested-by: Andi Kleen <ak@linux.intel.com> > Cc: Paolo Bonzini <pbonzini@redhat.com> > Cc: Nadav Amit <namit@vmware.com> > Cc: Andi Kleen <ak@linux.intel.com> > Cc: Josh Poimboeuf <jpoimboe@redhat.com> > Cc: Martin Jambor <mjambor@suse.cz> > Cc: Arnd Bergmann <arnd@arndb.de> > Cc: Steven Rostedt <rostedt@goodmis.org> > Cc: Miroslav Benes <mbenes@suse.cz> > Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com> > --- > include/linux/compiler_attributes.h | 8 +------- > 1 file changed, 1 insertion(+), 7 deletions(-) > > diff --git a/include/linux/compiler_attributes.h b/include/linux/compiler_attributes.h > index f8c400ba1929..f3e16fc9a5df 100644 > --- a/include/linux/compiler_attributes.h > +++ b/include/linux/compiler_attributes.h > @@ -163,17 +163,11 @@ > > /* > * Optional: not supported by clang > - * Note: icc does not recognize gcc's no-tracer > * > * gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Function-Attributes.html#index-noclone-function-attribute > - * gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Function-Attributes.html#index-optimize-function-attribute > */ > #if __has_attribute(__noclone__) > -# if __has_attribute(__optimize__) > -# define __noclone __attribute__((__noclone__, __optimize__("no-tracer"))) > -# else > -# define __noclone __attribute__((__noclone__)) > -# endif > +# define __noclone __attribute__((__noclone__)) > #else > # define __noclone > #endif Please also remove the line: # define __GCC4_has_attribute___optimize__ 1 in the top of the file. :-) With that change: Reviewed-by: Miguel Ojeda <miguel.ojeda.sandonis@gmail.com> Cheers, Miguel
On 21/12/18 12:34, Miguel Ojeda wrote: > Please also remove the line: > > # define __GCC4_has_attribute___optimize__ 1 > > in the top of the file. :-) > > With that change: > > Reviewed-by: Miguel Ojeda <miguel.ojeda.sandonis@gmail.com> Done, thanks. Paolo
On Thu, 20 Dec 2018, Sean Christopherson wrote: > The -ftracer optimization was disabled in __noclone as a workaround to > GCC duplicating a blob of inline assembly that happened to define a > global variable. It has been pointed out that no amount of workarounds > can guarantee the compiler won't duplicate inline assembly[1], and that > disabling the -ftracer optimization has several unintended and nasty > side effects[2][3]. > > Now that the offending KVM code which required the workaround has > been properly fixed and no longer uses __noclone, remove the -ftracer > optimization tweak from __noclone. > > [1] https://lore.kernel.org/lkml/ri6y38lo23g.fsf@suse.cz/T/#u > [2] https://lore.kernel.org/lkml/20181218140105.ajuiglkpvstt3qxs@treble/T/#u > [3] https://patchwork.kernel.org/patch/8707981/#21817015 > > This reverts commit 95272c29378ee7dc15f43fa2758cb28a5913a06d. > > Suggested-by: Andi Kleen <ak@linux.intel.com> > Cc: Paolo Bonzini <pbonzini@redhat.com> > Cc: Nadav Amit <namit@vmware.com> > Cc: Andi Kleen <ak@linux.intel.com> > Cc: Josh Poimboeuf <jpoimboe@redhat.com> > Cc: Martin Jambor <mjambor@suse.cz> > Cc: Arnd Bergmann <arnd@arndb.de> > Cc: Steven Rostedt <rostedt@goodmis.org> > Cc: Miroslav Benes <mbenes@suse.cz> > Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com> with Miguel's change Reviewed-by: Miroslav Benes <mbenes@suse.cz> Miroslav
diff --git a/include/linux/compiler_attributes.h b/include/linux/compiler_attributes.h index f8c400ba1929..f3e16fc9a5df 100644 --- a/include/linux/compiler_attributes.h +++ b/include/linux/compiler_attributes.h @@ -163,17 +163,11 @@ /* * Optional: not supported by clang - * Note: icc does not recognize gcc's no-tracer * * gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Function-Attributes.html#index-noclone-function-attribute - * gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Function-Attributes.html#index-optimize-function-attribute */ #if __has_attribute(__noclone__) -# if __has_attribute(__optimize__) -# define __noclone __attribute__((__noclone__, __optimize__("no-tracer"))) -# else -# define __noclone __attribute__((__noclone__)) -# endif +# define __noclone __attribute__((__noclone__)) #else # define __noclone #endif
The -ftracer optimization was disabled in __noclone as a workaround to GCC duplicating a blob of inline assembly that happened to define a global variable. It has been pointed out that no amount of workarounds can guarantee the compiler won't duplicate inline assembly[1], and that disabling the -ftracer optimization has several unintended and nasty side effects[2][3]. Now that the offending KVM code which required the workaround has been properly fixed and no longer uses __noclone, remove the -ftracer optimization tweak from __noclone. [1] https://lore.kernel.org/lkml/ri6y38lo23g.fsf@suse.cz/T/#u [2] https://lore.kernel.org/lkml/20181218140105.ajuiglkpvstt3qxs@treble/T/#u [3] https://patchwork.kernel.org/patch/8707981/#21817015 This reverts commit 95272c29378ee7dc15f43fa2758cb28a5913a06d. Suggested-by: Andi Kleen <ak@linux.intel.com> Cc: Paolo Bonzini <pbonzini@redhat.com> Cc: Nadav Amit <namit@vmware.com> Cc: Andi Kleen <ak@linux.intel.com> Cc: Josh Poimboeuf <jpoimboe@redhat.com> Cc: Martin Jambor <mjambor@suse.cz> Cc: Arnd Bergmann <arnd@arndb.de> Cc: Steven Rostedt <rostedt@goodmis.org> Cc: Miroslav Benes <mbenes@suse.cz> Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com> --- include/linux/compiler_attributes.h | 8 +------- 1 file changed, 1 insertion(+), 7 deletions(-)