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x86/percpu: Use %RIP-relative address in untagged_addr()

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%RIP-relative addresses are nowadays correctly handled in alternative
instructions, so remove misleading comment and improve assembly to
use %RIP-relative address.

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>
Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Acked-by: Peter Zijlstra (Intel) <peterz@infradaed.org>
Acked-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Link: https://lore.kernel.org/all/20231213150357.5942-1-ubizjak%40gmail.com
This commit is contained in:
Uros Bizjak 2023-12-13 16:03:15 +01:00 committed by Ingo Molnar
parent 86ed430cf5
commit de8c6a3521
1 changed files with 4 additions and 7 deletions
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11
arch/x86/include/asm/uaccess_64.h
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@ -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;
}