Messages in this thread | | | Date | Fri, 17 Nov 2023 10:41:03 +0100 | From | Peter Zijlstra <> | Subject | Re: [PATCH -tip] x86/mm: Use %RIP-relative address in untagged_addr() |
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On Thu, Nov 16, 2023 at 08:10:59PM +0100, Uros Bizjak wrote: > %RIP-relative addresses are nowadays correctly handled in alternative > instructions, so remove misleading comment and improve assembly to > use %RIP-relative address.
Ha!, it might've been this exact case (and Kirill grumbling) that got me to fix the alternative code :-)
> Also, explicitly using %gs: prefix will segfault for non-SMP builds. > Use macros from percpu.h which will DTRT with segment prefix register > as far as SMP/non-SMP builds are concerned.
> Signed-off-by: Uros Bizjak <ubizjak@gmail.com>
Acked-byL Peter Zijlstra (Intel) <peterz@infradaed.org>
> --- > arch/x86/include/asm/uaccess_64.h | 11 ++++------- > 1 file changed, 4 insertions(+), 7 deletions(-) > > diff --git a/arch/x86/include/asm/uaccess_64.h b/arch/x86/include/asm/uaccess_64.h > index f2c02e4469cc..01455c0b070c 100644 > --- a/arch/x86/include/asm/uaccess_64.h > +++ b/arch/x86/include/asm/uaccess_64.h > @@ -11,6 +11,7 @@ > #include <asm/alternative.h> > #include <asm/cpufeatures.h> > #include <asm/page.h> > +#include <asm/percpu.h> > > #ifdef CONFIG_ADDRESS_MASKING > /* > @@ -18,14 +19,10 @@ > */ > static inline unsigned long __untagged_addr(unsigned long addr) > { > - /* > - * Refer tlbstate_untag_mask directly to avoid RIP-relative relocation > - * in alternative instructions. The relocation gets wrong when gets > - * copied to the target place. > - */ > asm (ALTERNATIVE("", > - "and %%gs:tlbstate_untag_mask, %[addr]\n\t", X86_FEATURE_LAM) > - : [addr] "+r" (addr) : "m" (tlbstate_untag_mask)); > + "and " __percpu_arg([mask]) ", %[addr]", X86_FEATURE_LAM) > + : [addr] "+r" (addr) > + : [mask] "m" (__my_cpu_var(tlbstate_untag_mask))); > > return addr; > } > -- > 2.41.0 >
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